do waves travel through air

• Random article
• Teaching guide
• Privacy & cookies

by Chris Woodford . Last updated: July 23, 2023.

Photo: Sound is energy we hear made by things that vibrate. Photo by William R. Goodwin courtesy of US Navy and Wikimedia Commons .

What is sound?

Photo: Sensing with sound: Light doesn't travel well through ocean water: over half the light falling on the sea surface is absorbed within the first meter of water; 100m down and only 1 percent of the surface light remains. That's largely why mighty creatures of the deep rely on sound for communication and navigation. Whales, famously, "talk" to one another across entire ocean basins, while dolphins use sound, like bats, for echolocation. Photo by Bill Thompson courtesy of US Fish and Wildlife Service .

Robert Boyle's classic experiment

Artwork: Robert Boyle's famous experiment with an alarm clock.

How sound travels

Artwork: Sound waves and ocean waves compared. Top: Sound waves are longitudinal waves: the air moves back and forth along the same line as the wave travels, making alternate patterns of compressions and rarefactions. Bottom: Ocean waves are transverse waves: the water moves back and forth at right angles to the line in which the wave travels.

The science of sound waves

Picture: Reflected sound is extremely useful for "seeing" underwater where light doesn't really travel—that's the basic idea behind sonar. Here's a side-scan sonar (reflected sound) image of a World War II boat wrecked on the seabed. Photo courtesy of U.S. National Oceanographic and Atmospheric Administration, US Navy, and Wikimedia Commons .

Whispering galleries and amphitheaters

Photos by Carol M. Highsmith: 1) The Capitol in Washington, DC has a whispering gallery inside its dome. Photo credit: The George F. Landegger Collection of District of Columbia Photographs in Carol M. Highsmith's America, Library of Congress , Prints and Photographs Division. 2) It's easy to hear people talking in the curved memorial amphitheater building at Arlington National Cemetery, Arlington, Virginia. Photo credit: Photographs in the Carol M. Highsmith Archive, Library of Congress , Prints and Photographs Division.

Measuring waves

Understanding amplitude and frequency, why instruments sound different, the speed of sound.

Photo: Breaking through the sound barrier creates a sonic boom. The mist you can see, which is called a condensation cloud, isn't necessarily caused by an aircraft flying supersonic: it can occur at lower speeds too. It happens because moist air condenses due to the shock waves created by the plane. You might expect the plane to compress the air as it slices through. But the shock waves it generates alternately expand and contract the air, producing both compressions and rarefactions. The rarefactions cause very low pressure and it's these that make moisture in the air condense, producing the cloud you see here. Photo by John Gay courtesy of US Navy and Wikimedia Commons .

Why does sound go faster in some things than in others?

Chart: Generally, sound travels faster in solids (right) than in liquids (middle) or gases (left)... but there are exceptions!

How to measure the speed of sound

Sound in practice, if you liked this article..., don't want to read our articles try listening instead, find out more, on this website.

• Electric guitars
• Speech synthesis
• Synthesizers

On other sites

• Explore Sound : A comprehensive educational site from the Acoustical Society of America, with activities for students of all ages.
• Sound Waves : A great collection of interactive science lessons from the University of Salford, which explains what sound waves are and the different ways in which they behave.

Educational books for younger readers

• Sound (Science in a Flash) by Georgia Amson-Bradshaw. Franklin Watts/Hachette, 2020. Simple facts, experiments, and quizzes fill this book; the visually exciting design will appeal to reluctant readers. Also for ages 7–9.
• Sound by Angela Royston. Raintree, 2017. A basic introduction to sound and musical sounds, including simple activities. Ages 7–9.
• Experimenting with Sound Science Projects by Robert Gardner. Enslow Publishers, 2013. A comprehensive 120-page introduction, running through the science of sound in some detail, with plenty of hands-on projects and activities (including welcome coverage of how to run controlled experiments using the scientific method). Ages 9–12.
• Cool Science: Experiments with Sound and Hearing by Chris Woodford. Gareth Stevens Inc, 2010. One of my own books, this is a short introduction to sound through practical activities, for ages 9–12.
• Adventures in Sound with Max Axiom, Super Scientist by Emily Sohn. Capstone, 2007. The original, graphic novel (comic book) format should appeal to reluctant readers. Ages 8–10.

Popular science

• The Sound Book: The Science of the Sonic Wonders of the World by Trevor Cox. W. W. Norton, 2014. An entertaining tour through everyday sound science.

Academic books

• Master Handbook of Acoustics by F. Alton Everest and Ken Pohlmann. McGraw-Hill Education, 2015. A comprehensive reference for undergraduates and sound-design professionals.
• The Science of Sound by Thomas D. Rossing, Paul A. Wheeler, and F. Richard Moore. Pearson, 2013. One of the most popular general undergraduate texts.

Text copyright © Chris Woodford 2009, 2021. All rights reserved. Full copyright notice and terms of use .

Rate this page

Tell your friends, cite this page, more to explore on our website....

• Get the book
• Send feedback

Advertisement

Understanding Sound Waves and How They Work

• Share Content on Facebook
• Share Content on LinkedIn
• Share Content on Flipboard
• Share Content on Reddit
• Share Content via Email

Sound. When a drum is struck, the drumhead vibrates and the vibrations are transmitted through the air in the form of sound waves . When they strike the ear, these waves produce the sensation of sound.

Technically, sound is defined as a mechanical disturbance traveling through an elastic medium — a material that tends to return to its original condition after being deformed. The medium doesn't have to be air. Metal, wood, stone, glass, water, and many other substances conduct sound — many of them even better than air.

The Basics of Sound

Sound waves, speed of sound, the behavior of a sound wave, sound quality, history of sound.

There are many sources of sound. Familiar kinds include the vibration of a person's vocal cords, vibrating strings (piano, violin), a vibrating column of air (trumpet, flute), and vibrating solids (a door when someone knocks). It's impossible to list them all because anything that imparts a disturbance to an elastic medium is a source of sound.

Sound can be described in terms of pitch — from the low rumble of distant thunder to the high-pitched buzzing of a mosquito — and loudness. Pitch and loudness , however, are subjective qualities; they depend in part on the hearer's sense of hearing. Objective, measurable qualities of sound include frequency and intensity, which are related to pitch and loudness. These terms, as well as others used in discussing sound, are best understood through an examination of sound waves and their behavior.

Speed of sound in various mediums

Air, like all matter, consists of molecules. Even a tiny region of air contains vast numbers of air molecules. The molecules are in constant motion, traveling randomly and at great speed. They constantly collide with and rebound from one another and strike and rebound from objects that are in contact with the air.

When an object vibrates it produces sound waves in the air. For example, when the head of a drum is hit with a mallet, the drumhead vibrates and produces sound waves. The vibrating drumhead produces sound waves because it moves alternately outward and inward, pushing against, then moving away from, the air next to it. The air particles that strike the drumhead while it is moving outward rebound from it with more than their normal energy and speed, having received a push from the drumhead.

These faster-moving molecules move into the surrounding air. For a moment, the region next to the drumhead has a greater-than-normal concentration of air molecules — it becomes a region of compression. As the faster-moving molecules overtake the air molecules in the surrounding air, they collide with them and pass on their extra energy. The region of compression moves outward as the energy from the vibrating drumhead is transferred to groups of molecules farther and farther away.

Air molecules that strike the drumhead while it's moving inward rebound from it with less than their normal energy and speed. For a moment, the region next to the drumhead has fewer air molecules than normal — it becomes a region of rarefaction. Molecules colliding with these slower-moving molecules also rebound with less speed than normal, and the region of rarefaction travels outward.

The nature of sound is captured through its fundamental characteristics : wavelength (the distance between wave peaks), amplitude (the height of the wave, corresponding to loudness), frequency (the number of waves passing a point per second, related to pitch), time period (the time it takes for one complete wave cycle to occur), and velocity (the speed at which the wave travels through a medium). These properties intertwine to craft the unique signature of every sound we hear.

The wave nature of sound becomes apparent when a graph is drawn to show the changes in the concentration of air molecules at some point as the alternating pulses of compression and rarefaction pass that point. The graph for a single pure tone, such as that produced by a vibrating tuning fork, would show a sine wave (illustrated here ). The curve shows the changes in concentration. It begins, arbitrarily, at some time when the concentration is normal and a compression pulse is just arriving. The distance of each point on the curve from the horizontal axis indicates how much the concentration varies from normal.

Each compression and the following rarefaction make up one cycle. (A cycle can also be measured from any point on the curve to the next corresponding point.) The frequency of a sound is measured in cycles per second or hertz (abbreviated Hz). The amplitude is the greatest amount by which the concentration of air molecules varies from the normal.

The wavelength of a sound is the distance the disturbance travels during one cycle. It's related to the sound's speed and frequency by the formula speed/frequency = wavelength. This means that high-frequency sounds have short wavelengths and low-frequency sounds have long wavelengths. The human ear can detect sounds with frequencies as low as 20 Hz and as high as 20,000 Hz. In still air at room temperature, sounds with these frequencies have wavelengths of 75 feet (23 m) and 0.68 inch (1.7 cm) respectively.

Intensity refers to the amount of energy transmitted by the disturbance. It's proportional to the square of the amplitude. Intensity is measured in watts per square centimeter or in decibels (db). The decibel scale is defined as follows: An intensity of 10-16 watts per square centimeter equals 0 db. (Written out in decimal form, 10-16 appears as 0.0000000000000001.) Each tenfold increase in watts per square centimeter means an increase of 10 db. Thus, an intensity of 10-15 watts per square centimeter can also be expressed as 10 db and an intensity of 10-4 (or 0.0001) watts per square centimeter as 120 db.

The intensity of sound drops rapidly with increasing distance from the source. For a small sound source radiating energy uniformly in all directions, intensity varies inversely with the square of the distance from the source. That is, at a distance of two feet from the source the intensity is one-fourth as great as it is at a distance of one foot; at three feet it is only one-ninth as great as at one foot, etc.

Pitch depends on the frequency ; in general, a rise in frequency causes a sensation of rising pitch. The ability to distinguish between two sounds that are close in frequency, however, decreases in the upper and lower parts of the audible frequency range. There is also variation from person to person in the ability to distinguish between two sounds of very nearly the same frequency. Some trained musicians can detect differences in frequency as small as 1 or 2 Hz.

Because of how the hearing mechanism functions, the perception of pitch is also affected by intensity. Thus, when a tuning fork vibrating at 440 Hz (the frequency of A above middle C on the piano) is brought closer to the ear, a slightly lower tone, as though the fork were vibrating more slowly, is heard.

When the source of a sound is moving at a relatively high speed, a stationary listener hears a sound higher in pitch when the source is moving toward him or her and a sound lower in pitch when the source is moving away. This phenomenon, known as the Doppler effect , is due to the wave nature of sound.

In general, an increase in intensity will cause a sensation of increased loudness. But loudness does not increase in direct proportion to intensity. A sound of 50 dB has ten times the intensity of a sound of 40 dB but is only twice as loud. Loudness doubles with each increase of 10 dB in intensity.

Loudness is also affected by frequency because the human ear is more sensitive to some frequencies than to others. The threshold of hearing — the lowest sound intensity that will produce the sensation of hearing for most people — is about 0 dB in the 2,000 to 5,000 Hz frequency range. For frequencies below and above this range, sounds must have greater intensity to be heard. Thus, for example, a sound of 100 Hz is barely audible at 30 dB; a sound of 10,000 Hz is barely audible at 20 dB. At 120 to 140 dB, most people experience physical discomfort or actual pain, and this level of intensity is referred to as the threshold of pain .

When we visualize waves, we often think of transverse waves — like the rolling waves on a beach — where the motion of the wave is perpendicular to the direction of energy transfer. However, sound waves are a different type altogether — a longitudinal wave. In longitudinal sound waves, such as sound waves produced by a vibrating drumhead or our vocal cords, the particles of the medium move parallel to the wave's direction of travel. This movement creates areas of compression and rarefaction in the medium — be it air, water, or a solid — which our ears interpret as sound. Understanding the difference between longitudinal and transverse waves is central to understanding sound.

The speed of sound depends on the elasticity and density of the medium through which it is traveling. In general, sound travels faster in liquids than in gases and faster in solids than in liquids. The greater the elasticity and the lower the density, the faster sound moves in a medium. The mathematical relationship is speed = (elasticity/density).

The effect of elasticity and density on the speed of sound can be seen by comparing the speed of sound in air, hydrogen, and iron. Air and hydrogen have nearly the same elastic properties, but the density of hydrogen is less than that of air. Sound travels faster (about 4 times as fast) in hydrogen than in air. Although the density of air is much less than that of iron, the elasticity of iron is very much greater than that of air. Sound travels faster (about 14 times as fast) in iron than in air.

The speed of sound in a material, particularly in a gas or liquid, varies with temperature because a change in temperature affects the material's density. In air, for example, the speed of sound increases with an increase in temperature . At 32 °F. (0 °C.), the speed of sound in air is 1,087 feet per second (331 m/s); at 68 °F. (20 °C.), it is 1,127 feet per second (343 m/s).

The terms subsonic and supersonic refer to the speed of an object, such as an airplane, in relation to the speed of sound in the surrounding air. A subsonic speed is below the speed of sound; a supersonic speed is above the speed of sound. An object traveling at supersonic speed produces shock waves rather than ordinary sound waves. A shock wave is a compression wave that, when produced in air, can usually be heard as a sonic boom .

The speeds of supersonic objects are often expressed in terms of Mach number — the ratio of the object's speed to the speed of sound in the surrounding air. Thus, an object traveling at Mach 1 is traveling at the speed of sound; at Mach 2, it is traveling at twice the speed of sound.

Like light waves and other waves, sound waves are reflected, refracted, and diffracted, and exhibit interference.

Sound is constantly being reflected off many different surfaces. Most of the time the reflected sound is not noticed, because two identical sounds that reach the human ear less than 1/15 of a second apart cannot be distinguished as separate sounds. When the reflected sound is heard separately, it's called an echo .

Sound is reflected from a surface at the same angle at which it strikes the surface. This fact makes it possible to focus sound by means of curved reflecting surfaces in the same way that curved mirrors can be used to focus light. It also accounts for the effects of so-called whispering galleries, rooms in which a word whispered at one point can be heard distinctly at some other point fairly far away, though it cannot be heard anywhere else in the room. (The National Statuary Hall of the United States Capitol is an example.) Reflection is also used to focus sound in a megaphone and when calling through cupped hands.

The reflection of sound can pose a serious problem in concert halls and auditoriums. In a poorly designed hall, a speaker's first word may reverberate (echo repeatedly) for several seconds, so that the listeners may hear all the words of a sentence echoing at the same time. Music can be similarly distorted. Such problems can usually be corrected by covering reflecting surfaces with sound-absorbing materials such as draperies or acoustical tiles. Clothing also absorbs sound; for this reason, reverberation is greater in an empty hall than in one filled with people. All these sound-absorbing materials are porous; sound waves entering the tiny air-filled spaces bounce around in them until their energy is spent. They are, in effect, trapped.

The reflection of sound is used by some animals, notably bats , for echolocation — locating, and in some cases identifying, objects through the sense of hearing rather than the sense of sight. Bats emit bursts of sound of frequencies far beyond the upper limits of human hearing. Sounds with short wavelengths are reflected even from very small objects. A bat can unerringly locate and catch even a mosquito in total darkness. Sonar is an artificial form of echolocation .

When a wave passes from one material to another at an angle, it usually changes speed, causing the wave front to bend. The refraction of sound can be demonstrated in a physics laboratory by using a lens-shaped balloon filled with carbon dioxide to bring sound waves to a focus.

Diffraction

When sound waves pass around an obstacle or through an opening in an obstacle, the edge of the obstacle or the opening acts as a secondary sound source, sending out waves of the same frequency and wavelength (but of lower intensity) as the original source. The spreading out of sound waves from the secondary source is called diffraction . Because of this phenomenon, sound can be heard around corners despite the fact that sound waves generally travel in a straight line.

Interference

Whenever waves interact, interference occurs. For sound waves, the phenomenon is perhaps best understood by thinking in terms of the compressions and rarefactions of the two waves as they arrive at some point. When the waves are in phase so that their compressions and rarefactions coincide, they reinforce each other ( constructive interference ). When they are out of phase, so that the compressions of one coincide with the rarefactions of the other, they tend to weaken or even cancel each other ( destructive interference ). The interaction between the two waves produces a resultant wave.

In auditoriums, destructive interference between sound from the stage and sound reflected from other parts of the hall can create dead spots in which both the volume and clarity of sound are poor. Such interference can be reduced by the use of sound-absorbing materials on reflecting surfaces. On the other hand, interference can improve an auditorium's acoustical qualities. This is done by arranging the reflecting surfaces in such a way that the level of sound is actually increased in the area in which the audience sits.

Interference between two waves of nearly but not quite equal frequencies produces a tone of alternately increasing and decreasing intensity because the two waves continually fall in and out of phase. The pulsations heard are called beats. Piano tuners make use of this effect, adjusting the tone of a string against that of a standard tuning fork until beats can no longer be heard.

Sound waves are fundamentally pressure waves, traveling through the compression and rarefaction of particles within a medium. Sound waves consist of areas where particles are bunched together, followed by areas where they're spread apart. These high-pressure and low-pressure regions propagate through environments such as air, water or solids, as the energy of the sound wave moves from particle to particle. It's the rapid variation in pressure that an ear drum detects and the brain decodes into the sounds we hear.

Sounds of a single pure frequency are produced only by tuning forks and electronic devices called oscillators ; most sounds are a mixture of tones of different frequencies and amplitudes. The tones produced by musical instruments have one important characteristic in common: they are periodic, that is, the vibrations occur in a repeating pattern. The oscilloscope trace of a trumpet's sound shows such a pattern. For most non-musical sounds, such as those of a bursting balloon or a person coughing, an oscilloscope trace would show a jagged, irregular pattern, indicating a jumble of frequencies and amplitudes.

A column of air, as that in a trumpet, and a piano string both have a fundamental frequency — the frequency at which they vibrate most readily when set in motion. For a vibrating column of air, that frequency is determined principally by the length of the column. (The trumpet's valves are used to change the effective length of the column.) For a vibrating string, the fundamental frequency depends on the string's length, its tension, and its mass per unit length.

In addition to its fundamental frequency, a string or vibrating column of air also produces overtones with frequencies that are whole-number multiples of the fundamental frequency. It is the number of overtones produced and their relative strength that gives a musical tone from a given source its distinctive quality or timbre . The addition of further overtones would produce a complicated pattern, such as that of the oscilloscope trace of the trumpet's sound.

How the fundamental frequency of a vibrating string depends on the string's length, tension, and mass per unit length is described by three laws:

1. The fundamental frequency of a vibrating string is inversely proportional to its length.

Reducing the length of a vibrating string by one-half will double its frequency, raising the pitch by one octave, if the tension remains the same.

2. The fundamental frequency of a vibrating string is directly proportional to the square root of the tension.

Increasing the tension of a vibrating string raises the frequency; if the tension is made four times as great, the frequency is doubled, and the pitch is raised by one octave.

3. The fundamental frequency of a vibrating string is inversely proportional to the square root of the mass per unit length.

This means that of two strings of the same material and with the same length and tension, the thicker string has the lower fundamental frequency. If the mass per unit length of one string is four times that of the other, the thicker string has a fundamental frequency one-half that of the thinner string and produces a tone one octave lower.

One of the first discoveries regarding sound was made in the sixth century B.C. by the Greek mathematician and philosopher Pythagoras . He noted the relationship between the length of a vibrating string and the tone it produces — what is now known as the first law of strings. Pythagoras may also have understood that the sensation of sound is caused by vibrations. Not long after his time it was recognized that this sensation depends on vibrations traveling through the air and striking the eardrum.

About 1640 the French mathematician Marin Mersenne conducted the first experiments to determine the speed of sound in air. Mersenne is also credited with discovering the second and third laws of strings. In 1660 the British scientist Robert Boyle demonstrated that the transmission of sound required a medium — by showing that the ringing of a bell in a jar from which the air had been pumped could not be heard.

Ernst Chladni , a German physicist, made extensive analyses of sound vibrations during the late 1700s and early 1800s. In the early 1800s, the French mathematician Fourier discovered that such complex waves as those produced by a vibrating string with all its overtones consist of a series of simple periodic waves.

An important contribution to the understanding of acoustics was made by Wallace Clement Sabine , a physicist at Harvard University, in the late 1890s. Sabine was asked to improve the acoustics of the main lecture hall in Harvard's Fogg Art Museum. He was first to measure reverberation time — which he found to be 5 1/2 seconds in the lecture hall. Experimenting first with seat cushions from a nearby theater, and later with other sound-absorbing materials and other methods, Sabine laid the foundation for architectural acoustics. He designed Boston Symphony Hall (opened in 1900), the first building with scientifically formulated acoustics.

In the second half of the 20th century, the rising level of noise in the modern world — particularly in urban areas — prompted a whole new series of investigations, dealing in large part with the physiological and psychological effects of noise on humans.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.

Please copy/paste the following text to properly cite this HowStuffWorks.com article:

Quesst Home

What's the science of sound, understanding sound waves, sonic booms, and the speed of sound are key to understanding how x-59 will quiet the boom., the physics of waves, waves are created when energy is transferred through a medium like water or air. there are two types of waves, transverse and longitudinal (sometimes called pressure or compression waves). when people think of waves, they often think of transverse waves. click each video to see an example and explanation of both types. longitudinal waves transverse waves, sound waves and units of measurement, sound waves are longitudinal waves that travel through a medium like air or water. when we think about sound, we often think about how loud it is (amplitude, or intensity) and its pitch (frequency)..

The speed of sound

Sonic booms

When an airplane flies at or above the speed of sound, air molecules cannot move out of the way of the airplane fast enough, so the pressure waves combine to generate a large shockwave, which people on the ground hear as a sonic boom..

Quieting the boom

At nasa, we’ve done over 70 years of supersonic research to help us understand and eventually quiet the boom.

• Skip to primary navigation
• Skip to main content
• Skip to footer

Science Struck

How Does Sound Travel? Here’s the Science Behind This Concept

When sound waves travel through a medium, the particles of the medium vibrate. Vibrations reach the ear and then the brain which senses them and we recognize sound. Read on for an explanation of how sound travels.

Like it? Share it!

Sound is a series of compression and rarefraction waves that can travel long distances. It is produced by the vibration of the particles present in its medium; a medium is the material through which sound can travel. Presence of a medium is a must for the movement of sound waves. There are various types of medium through which sound waves can move like solids, liquids, gases, plasma, etc. Sound cannot travel through vacuum.

Characteristics of Sound Waves

The speed and the physical characteristics of sound largely varies with the change in its ambient conditions. The speed of sound depends on the density of the medium though which it is traveling. If its density is quite high, then sound would travel at a faster pace. When sound travels through gaseous medium, its speed varies with respect to changes in temperature.

The frequency of sound waves is nothing but the total number of vibrations that have been produced. The length of sound waves vary according to its frequency. Sound waves with long wavelengths have low frequency or low pitch; and those with short wavelengths have high frequency or high pitch. Our ears are capable of hearing only those sound waves which lie in the range between 20 and 20,000 vibrations per second.

How do Sound Waves Travel?

Basically, there are three things that are required for the transmission of sound. They are: a source that can transmit the sound, a medium through which sound can pass (like, water, air, etc.), and the receiver or the detector which receives the sound. The traveling process of sound has been explained below.

Creation of Sound

When a physical object moves in air, it causes vibrations which leads to formation of a series of compression waves in the air. These waves travel in the form of sound. For instance, when we strum the strings of a guitar or hit the head of a drum, the to-and-fro motion of the strings or the drum head creates compression waves of sound in the surrounding air. Similarly, when we speak, our vocal cords vibrate and the sound is created. This type of vibration occurs not just in atmospheric air but in other mediums like, solids and liquids as well. For instance, when a train is moving on a railroad made up of steel, the sound waves thus produced travel via these tracks.

At room temperature, sound travels through air with a speed of 343 m/s, through water at 1,482 m/s, and through steel at 5,960 m/s. As you can see, sound waves travel in a gaseous medium at a slow pace because its molecules are loosely bound and have to cover a long distance to collide with another molecule. In solid medium, the atoms are so closely packed that the vibration is readily transmitted to the neighboring atoms, and sound travels quite fast. In liquid medium, the bonding between the component particles are not as strong as in solids. Therefore, the sound waves move through it at a less speed as compared to solid.

Detection of Sound

When the sound waves hit the receiver, it causes some vibration in that object. The detector captures just a part of the energy from the moving sound wave. This energy of vibration is then converted to electrical signals. Thus, when the sound waves reach our ears, the eardrum present inside it vibrates. This vibration reaches our inner ear and is converted into nerve signals. As a result, we can hear the sound. Devices like microphone can detect sound. The sound waves create vibrations in its membrane which forms electrical signals that gets amplified and recorded.

So, how does sound travel? Vibration of an object causes vibrations of the same frequency in the surrounding medium. The vibrations are sent to the inner ear. After the auditory nerve picks up these vibrations, electrical signals are sent to the brain where the vibrations are recognized as sound.

Get Updates Right to Your Inbox

Privacy overview.

• svg]:fill-accent-900 [&>svg]:stroke-accent-900">

How do sound waves work?

By Brian S. Hawkins

Updated on Jun 1, 2023 2:00 PM EDT

We live our entire lives surrounded by them. They slam into us constantly at more than 700 miles per hour, sometimes hurting, sometimes soothing . They have the power to communicate ideas, evoke fond memories, start fights, entertain an audience, scare the heck out of us, or help us fall in love. They can trigger a range of emotions and they even cause physical damage. This reads like something out of science fiction , but what we’re talking about is very much real and already part of our day-to-day lives. They’re sound waves. So, what are sound waves and how do they work?

If you’re not in the industry of audio, you probably don’t think too much about the mechanics of sound. Sure, most people care about how sounds make them feel, but they aren’t as concerned with how the sound actually affects them. Understanding how sound works does have a number of practical applications , however, and you don’t have to be a physicist or engineer to explore this fascinating subject. Here’s a primer on the science of sound to help get you started.

What’s in a wave

When energy moves through a substance such as water or air, it makes a wave. There are two kinds of waves: longitudinal ones and transverse ones. Transverse waves, as NASA notes , are probably what most people think of when they picture waves—like the up-down ripples of a battle rope used to work out. Longitudinal waves are also known as compression waves, and that’s what sound waves are. There’s no perpendicular motion to these, rather, the wave moves in the same direction as the disturbance.

How sound waves work

Sound waves are a type of energy that’s released when an object vibrates. Those acoustic waves travel from their source through air or another medium, and when they come into contact with our eardrums, our brains translate the pressure waves into words, music, or signals we can understand. These pulses help you place where things are in your environment.

We can experience sound waves in ways that are more physical, not just physiological, too. If sound waves reach  a microphone —whether it’s a plug-n-play  USB livestream mic  or a studio-quality  microphone for vocals —it transforms them into electronic impulses that are turned back into sound by vibrating speakers . Whether listening at home or at a concert, we can feel the deep bass in our chest. Opera singers can use them to shatter glass. It’s even possible to see sound waves sent through a medium like sand, which leaves behind a kind of sonic footprint. 

That shape is rolling peaks and valleys, the signature of a sine (aka sinusoid) wave. If the wave travels faster, those peaks and valleys form closer together. If it moves slower, they spread out. It’s not a poor analogy to think of them somewhat like waves in the ocean. It’s this movement that allows sound waves to do so many other things. 

It’s all about frequency

When we talk about a sound wave’s speed, we’re referring to how fast these longitudinal waves move from peak to trough and back to peak. Up … and then down … and then up … and then down. The technical term is frequency , but many of us know it as pitch. We measure sound frequency in hertz (Hz), which represents cycles-per-second, with faster frequencies creating higher-pitched sounds. For instance, the A note right above Middle C on a piano is measured at 440 Hz—it travels up and down at 440 cycles per second. Middle C itself is 261.63 Hz—a lower pitch, vibrating at a slower frequency.

Understanding frequencies can be useful in many ways. You can precisely tune an instrument by analyzing the frequencies of its strings. Recording engineers use their understanding of frequency ranges to dial in equalization settings that help sculpt the sound of the music they’re mixing . Car designers work with frequencies—and materials that can block them—to help make engines quieter. And  active noise cancellation  uses artificial intelligence and algorithms to measure external frequencies and generate inverse waves to cancel environmental rumble and hum, allowing top-tier ANC headphones and earphones to isolate the wearer from the noise around them. The average frequency range of human hearing is 20 to 20,000 Hz.

What’s in a name? 

The hertz measurement is named for the German physicist Heinrich Rudolf Hertz , who proved the existence of electromagnetic waves. 

Getting amped

Amplitude equates to sound’s volume or intensity. Using our ocean analogy—because, hey, it works—amplitude describes the height of the waves.

We measure amplitude in decibels (dB). The dB scale is logarithmic, which means there’s a fixed ratio between measurement units. And what does that mean? Let’s say you have a dial on your guitar amp with evenly spaced steps on it numbered one through five. If the knob is following a logarithmic scale, the volume won’t increase evenly as you turn the dial from marker to marker. If the ratio is 4, let’s say, then turning the dial from the first to the second marker increases the sound by 4 dB. But going from the second to the third marker increases it by 16 dB. Turn the dial again and your amp becomes 64 dB louder. Turn it once more, and you’ll blast out a blistering 256 dB—more than loud enough to rupture your eardrums. But if you’re somehow still standing, you can turn that knob one more time to increase your volume to a brain-walloping 1,024 decibels. That’s almost 10 times louder than any rock concert you’ll ever encounter, and it will definitely get you kicked out of your rehearsal space. All of which is why real amps aren’t designed that way.

Twice as nice

We interpret a 10 dB increase in amplitude as a doubling of volume. 

Parts of a sound wave

Timbre and envelope are two characteristics of sound waves that help determine why, say, two instruments can play the same chords but sound nothing alike. 

Timbre is determined by the unique harmonics formed by the combination of notes in a chord. The A in an A chord is only its fundamental note—you also have overtones and undertones. The way these sound together helps keep a piano from sounding like a guitar, or an angry grizzly bear from sounding like a rumbling tractor engine. 

[Related: Even plants pick up on good vibes ]

But we also rely on envelopes, which determine how a sound’s amplitude changes over time. A cello’s note might swell slowly to its maximum volume, then hold for a bit before gently fading out again. On the other hand, a slamming door delivers a quick, sharp, loud sound that cuts off almost instantly. Envelopes comprise four parts: Attack, Decay, Sustain, and Release. In fact, they’re more formally known as ADSR Envelopes. 

• Attack: This is how quickly the sound achieves its maximum volume. A barking dog has a very short attack; a rising orchestra has a slower one. 
• Decay: This describes how fast the sound settles into its sustained volume. When a guitar player plucks a string, the note starts off loudly but quickly settles into something quieter before fading out completely. The time it takes to hit that sustained volume is decay. 
• Sustain: Sustain isn’t a measure of time; it’s a measure of amplitude, or volume. It’s how loud the plucked guitar note is after the initial attack but before it fades out. 
• Release: This is the time it takes for the note to drift off to silence. 

Speed of sound

Science fiction movies like it when spaceships explode with giant, rumbling, surround-sound booms . However, sound needs to travel through a medium so, despite Hollywood saying otherwise, you’d never hear an explosion in the vacuum of space. 

Sound’s velocity , or the speed it travels at , differs depending on the density (and even temperature) of the medium it’s moving through—it’s faster in the air than water, for instance. Generally, sound moves at 1,127 feet per second, or 767.54 miles per hour. When jets break the sound barrier , they’re traveling faster than that. And knowing these numbers lets you estimate the distance of a lightning strike by counting the time between the flash and thunder’s boom—if you count to 10, it’s approximately 11,270 feet away, or about a quarter-mile. (Very roughly, of course.) 

A stimulating experience

Anyone can benefit from understanding the fundamentals of sound and what sound waves are. Musicians and content creators with home recording set-ups and studio monitors obviously need a working knowledge of frequencies and amplitude. If you host a podcast, you’ll want as many tools as possible to ensure your voice sounds clear and rich, and this can include understanding the frequencies of your voice, what microphones are best suited to them , and how to set up your room to reflect or dampen the sounds you do or do not want. Having some foundational information is also useful when doing home-improvement projects— when treating a recording workstation , for instance, or just soundproofing a new enclosed deck. And who knows, maybe one day you’ll want to shatter glass. Having a better understanding of the physics of sound opens up wonderful new ways to explore and experience the world around us. Now, go out there and make some noise!

This post has been updated. It was originally published on July 27, 2021.

• Anatomy & Physiology
• Astrophysics
• Earth Science
• Environmental Science
• Organic Chemistry
• Precalculus
• Trigonometry
• English Grammar
• U.S. History
• World History

... and beyond

• Socratic Meta
• Featured Answers

• Sound waves

Key Questions

Scientifically, this is a very difficult question to answer. The reason is simply that the word "best" is difficult to interpret. In science, understanding the question is often as important as the answer.

You might be asking about the speed of sound. You might be asking about energy loss of sound (e.g. sound traveling through cotton).

Then again, you might be asking about materials which transmit a range of frequencies with very little dispersion (difference between the wave speeds for various pitches). You might look up soliton waves in narrow channels for an example of a wave that stays together over a long distance.

And yet again, you might be asking about materials which can pickup sound from air; an impedance match.

What materials have the highest speed of sound? This is the easiest question to answer, so we'll start with that. In general, the speed of sound in a material varies with the stiffness and mass of that material. Sound traveling through hardened steel will cary much faster than traveling through air. Many materials are characterized by something called a Young's Modulus. You should find that the speed of sound increases with higher Young's Modulus. A search for materials with a high speed of sound or a high Young's Modulus should turn up interesting answers.

One of the most dense materials known is the neutron star. One drop-sized piece of a neutron star has the same mass greater than the giant pyramid at Giza (about a billion tons). Some people calculate the speed of sound in a neutron star to be very close to the speed of light.

• TPC and eLearning
• What's NEW at TPC?
• Read Watch Interact
• Practice Review Test
• Teacher-Tools
• Request a Demo
• Get A Quote
• Subscription Selection
• Seat Calculator
• Ad Free Account
• Edit Profile Settings
• Metric Conversions Questions
• Metric System Questions
• Metric Estimation Questions
• Significant Digits Questions
• Proportional Reasoning
• Acceleration
• Distance-Displacement
• Dots and Graphs
• Graph That Motion
• Match That Graph
• Name That Motion
• Motion Diagrams
• Pos'n Time Graphs Numerical
• Pos'n Time Graphs Conceptual
• Up And Down - Questions
• Balanced vs. Unbalanced Forces
• Change of State
• Force and Motion
• Mass and Weight
• Match That Free-Body Diagram
• Net Force (and Acceleration) Ranking Tasks
• Newton's Second Law
• Normal Force Card Sort
• Recognizing Forces
• Air Resistance and Skydiving
• Solve It! with Newton's Second Law
• Which One Doesn't Belong?
• Component Addition Questions
• Head-to-Tail Vector Addition
• Projectile Mathematics
• Trajectory - Angle Launched Projectiles
• Trajectory - Horizontally Launched Projectiles
• Vector Addition
• Vector Direction
• Which One Doesn't Belong? Projectile Motion
• Forces in 2-Dimensions
• Being Impulsive About Momentum
• Explosions - Law Breakers
• Hit and Stick Collisions - Law Breakers
• Case Studies: Impulse and Force
• Impulse-Momentum Change Table
• Keeping Track of Momentum - Hit and Stick
• Keeping Track of Momentum - Hit and Bounce
• What's Up (and Down) with KE and PE?
• Energy Conservation Questions
• Energy Dissipation Questions
• Energy Ranking Tasks
• LOL Charts (a.k.a., Energy Bar Charts)
• Match That Bar Chart
• Words and Charts Questions
• Name That Energy
• Stepping Up with PE and KE Questions
• Case Studies - Circular Motion
• Circular Logic
• Forces and Free-Body Diagrams in Circular Motion
• Gravitational Field Strength
• Universal Gravitation
• Angular Position and Displacement
• Linear and Angular Velocity
• Angular Acceleration
• Rotational Inertia
• Balanced vs. Unbalanced Torques
• Getting a Handle on Torque
• Torque-ing About Rotation
• Properties of Matter
• Fluid Pressure
• Buoyant Force
• Sinking, Floating, and Hanging
• Pascal's Principle
• Flow Velocity
• Bernoulli's Principle
• Balloon Interactions
• Charge and Charging
• Charge Interactions
• Charging by Induction
• Conductors and Insulators
• Coulombs Law
• Electric Field
• Electric Field Intensity
• Polarization
• Case Studies: Electric Power
• Know Your Potential
• Light Bulb Anatomy
• I = ∆V/R Equations as a Guide to Thinking
• Parallel Circuits - ∆V = I•R Calculations
• Resistance Ranking Tasks
• Series Circuits - ∆V = I•R Calculations
• Series vs. Parallel Circuits
• Equivalent Resistance
• Period and Frequency of a Pendulum
• Pendulum Motion: Velocity and Force
• Energy of a Pendulum
• Period and Frequency of a Mass on a Spring
• Horizontal Springs: Velocity and Force
• Vertical Springs: Velocity and Force
• Energy of a Mass on a Spring
• Decibel Scale
• Frequency and Period
• Closed-End Air Columns
• Name That Harmonic: Strings
• Rocking the Boat
• Wave Basics
• Matching Pairs: Wave Characteristics
• Wave Interference
• Waves - Case Studies
• Color Addition and Subtraction
• Color Filters
• If This, Then That: Color Subtraction
• Light Intensity
• Color Pigments
• Converging Lenses
• Curved Mirror Images
• Law of Reflection
• Refraction and Lenses
• Total Internal Reflection
• Who Can See Who?
• Lab Equipment
• Lab Procedures
• Formulas and Atom Counting
• Atomic Models
• Bond Polarity
• Entropy Questions
• Cell Voltage Questions
• Heat of Formation Questions
• Reduction Potential Questions
• Oxidation States Questions
• Measuring the Quantity of Heat
• Hess's Law
• Oxidation-Reduction Questions
• Galvanic Cells Questions
• Thermal Stoichiometry
• Molecular Polarity
• Quantum Mechanics
• Balancing Chemical Equations
• Bronsted-Lowry Model of Acids and Bases
• Classification of Matter
• Collision Model of Reaction Rates
• Density Ranking Tasks
• Dissociation Reactions
• Complete Electron Configurations
• Elemental Measures
• Enthalpy Change Questions
• Equilibrium Concept
• Equilibrium Constant Expression
• Equilibrium Calculations - Questions
• Equilibrium ICE Table
• Intermolecular Forces Questions
• Ionic Bonding
• Lewis Electron Dot Structures
• Limiting Reactants
• Line Spectra Questions
• Mass Stoichiometry
• Measurement and Numbers
• Metals, Nonmetals, and Metalloids
• Metric Estimations
• Metric System
• Molarity Ranking Tasks
• Mole Conversions
• Name That Element
• Names to Formulas
• Names to Formulas 2
• Nuclear Decay
• Particles, Words, and Formulas
• Periodic Trends
• Precipitation Reactions and Net Ionic Equations
• Pressure Concepts
• Pressure-Temperature Gas Law
• Pressure-Volume Gas Law
• Chemical Reaction Types
• Significant Digits and Measurement
• States Of Matter Exercise
• Stoichiometry Law Breakers
• Stoichiometry - Math Relationships
• Subatomic Particles
• Spontaneity and Driving Forces
• Gibbs Free Energy
• Volume-Temperature Gas Law
• Acid-Base Properties
• Energy and Chemical Reactions
• Chemical and Physical Properties
• Valence Shell Electron Pair Repulsion Theory
• Writing Balanced Chemical Equations
• Mission CG1
• Mission CG10
• Mission CG2
• Mission CG3
• Mission CG4
• Mission CG5
• Mission CG6
• Mission CG7
• Mission CG8
• Mission CG9
• Mission EC1
• Mission EC10
• Mission EC11
• Mission EC12
• Mission EC2
• Mission EC3
• Mission EC4
• Mission EC5
• Mission EC6
• Mission EC7
• Mission EC8
• Mission EC9
• Mission RL1
• Mission RL2
• Mission RL3
• Mission RL4
• Mission RL5
• Mission RL6
• Mission KG7
• Mission RL8
• Mission KG9
• Mission RL10
• Mission RL11
• Mission RM1
• Mission RM2
• Mission RM3
• Mission RM4
• Mission RM5
• Mission RM6
• Mission RM8
• Mission RM10
• Mission LC1
• Mission RM11
• Mission LC2
• Mission LC3
• Mission LC4
• Mission LC5
• Mission LC6
• Mission LC8
• Mission SM1
• Mission SM2
• Mission SM3
• Mission SM4
• Mission SM5
• Mission SM6
• Mission SM8
• Mission SM10
• Mission KG10
• Mission SM11
• Mission KG2
• Mission KG3
• Mission KG4
• Mission KG5
• Mission KG6
• Mission KG8
• Mission KG11
• Mission F2D1
• Mission F2D2
• Mission F2D3
• Mission F2D4
• Mission F2D5
• Mission F2D6
• Mission KC1
• Mission KC2
• Mission KC3
• Mission KC4
• Mission KC5
• Mission KC6
• Mission KC7
• Mission KC8
• Mission AAA
• Mission SM9
• Mission LC7
• Mission LC9
• Mission NL1
• Mission NL2
• Mission NL3
• Mission NL4
• Mission NL5
• Mission NL6
• Mission NL7
• Mission NL8
• Mission NL9
• Mission NL10
• Mission NL11
• Mission NL12
• Mission MC1
• Mission MC10
• Mission MC2
• Mission MC3
• Mission MC4
• Mission MC5
• Mission MC6
• Mission MC7
• Mission MC8
• Mission MC9
• Mission RM7
• Mission RM9
• Mission RL7
• Mission RL9
• Mission SM7
• Mission SE1
• Mission SE10
• Mission SE11
• Mission SE12
• Mission SE2
• Mission SE3
• Mission SE4
• Mission SE5
• Mission SE6
• Mission SE7
• Mission SE8
• Mission SE9
• Mission VP1
• Mission VP10
• Mission VP2
• Mission VP3
• Mission VP4
• Mission VP5
• Mission VP6
• Mission VP7
• Mission VP8
• Mission VP9
• Mission WM1
• Mission WM2
• Mission WM3
• Mission WM4
• Mission WM5
• Mission WM6
• Mission WM7
• Mission WM8
• Mission WE1
• Mission WE10
• Mission WE2
• Mission WE3
• Mission WE4
• Mission WE5
• Mission WE6
• Mission WE7
• Mission WE8
• Mission WE9
• Vector Walk Interactive
• Name That Motion Interactive
• Kinematic Graphing 1 Concept Checker
• Kinematic Graphing 2 Concept Checker
• Graph That Motion Interactive
• Two Stage Rocket Interactive
• Rocket Sled Concept Checker
• Force Concept Checker
• Free-Body Diagrams Concept Checker
• Free-Body Diagrams The Sequel Concept Checker
• Skydiving Concept Checker
• Elevator Ride Concept Checker
• Vector Addition Concept Checker
• Vector Walk in Two Dimensions Interactive
• Name That Vector Interactive
• River Boat Simulator Concept Checker
• Projectile Simulator 2 Concept Checker
• Projectile Simulator 3 Concept Checker
• Hit the Target Interactive
• Turd the Target 1 Interactive
• Turd the Target 2 Interactive
• Balance It Interactive
• Go For The Gold Interactive
• Egg Drop Concept Checker
• Fish Catch Concept Checker
• Exploding Carts Concept Checker
• Collision Carts - Inelastic Collisions Concept Checker
• Its All Uphill Concept Checker
• Stopping Distance Concept Checker
• Chart That Motion Interactive
• Roller Coaster Model Concept Checker
• Uniform Circular Motion Concept Checker
• Horizontal Circle Simulation Concept Checker
• Vertical Circle Simulation Concept Checker
• Race Track Concept Checker
• Gravitational Fields Concept Checker
• Orbital Motion Concept Checker
• Angular Acceleration Concept Checker
• Balance Beam Concept Checker
• Torque Balancer Concept Checker
• Aluminum Can Polarization Concept Checker
• Charging Concept Checker
• Name That Charge Simulation
• Coulomb's Law Concept Checker
• Electric Field Lines Concept Checker
• Put the Charge in the Goal Concept Checker
• Circuit Builder Concept Checker (Series Circuits)
• Circuit Builder Concept Checker (Parallel Circuits)
• Circuit Builder Concept Checker (∆V-I-R)
• Circuit Builder Concept Checker (Voltage Drop)
• Equivalent Resistance Interactive
• Pendulum Motion Simulation Concept Checker
• Mass on a Spring Simulation Concept Checker
• Particle Wave Simulation Concept Checker
• Boundary Behavior Simulation Concept Checker
• Slinky Wave Simulator Concept Checker
• Simple Wave Simulator Concept Checker
• Wave Addition Simulation Concept Checker
• Standing Wave Maker Simulation Concept Checker
• Color Addition Concept Checker
• Painting With CMY Concept Checker
• Stage Lighting Concept Checker
• Filtering Away Concept Checker
• InterferencePatterns Concept Checker
• Young's Experiment Interactive
• Plane Mirror Images Interactive
• Who Can See Who Concept Checker
• Optics Bench (Mirrors) Concept Checker
• Name That Image (Mirrors) Interactive
• Refraction Concept Checker
• Total Internal Reflection Concept Checker
• Optics Bench (Lenses) Concept Checker
• Kinematics Preview
• Velocity Time Graphs Preview
• Moving Cart on an Inclined Plane Preview
• Stopping Distance Preview
• Cart, Bricks, and Bands Preview
• Fan Cart Study Preview
• Friction Preview
• Coffee Filter Lab Preview
• Friction, Speed, and Stopping Distance Preview
• Up and Down Preview
• Projectile Range Preview
• Ballistics Preview
• Juggling Preview
• Marshmallow Launcher Preview
• Air Bag Safety Preview
• Colliding Carts Preview
• Collisions Preview
• Engineering Safer Helmets Preview
• Push the Plow Preview
• Its All Uphill Preview
• Energy on an Incline Preview
• Modeling Roller Coasters Preview
• Hot Wheels Stopping Distance Preview
• Ball Bat Collision Preview
• Energy in Fields Preview
• Weightlessness Training Preview
• Roller Coaster Loops Preview
• Universal Gravitation Preview
• Keplers Laws Preview
• Kepler's Third Law Preview
• Charge Interactions Preview
• Sticky Tape Experiments Preview
• Wire Gauge Preview
• Voltage, Current, and Resistance Preview
• Light Bulb Resistance Preview
• Series and Parallel Circuits Preview
• Thermal Equilibrium Preview
• Linear Expansion Preview
• Heating Curves Preview
• Electricity and Magnetism - Part 1 Preview
• Electricity and Magnetism - Part 2 Preview
• Vibrating Mass on a Spring Preview
• Period of a Pendulum Preview
• Wave Speed Preview
• Slinky-Experiments Preview
• Standing Waves in a Rope Preview
• Sound as a Pressure Wave Preview
• DeciBel Scale Preview
• DeciBels, Phons, and Sones Preview
• Sound of Music Preview
• Shedding Light on Light Bulbs Preview
• Models of Light Preview
• Electromagnetic Radiation Preview
• Electromagnetic Spectrum Preview
• EM Wave Communication Preview
• Digitized Data Preview
• Light Intensity Preview
• Concave Mirrors Preview
• Object Image Relations Preview
• Snells Law Preview
• Reflection vs. Transmission Preview
• Magnification Lab Preview
• Reactivity Preview
• Ions and the Periodic Table Preview
• Periodic Trends Preview
• Chemical Reactions Preview
• Intermolecular Forces Preview
• Melting Points and Boiling Points Preview
• Bond Energy and Reactions Preview
• Reaction Rates Preview
• Ammonia Factory Preview
• Stoichiometry Preview
• Nuclear Chemistry Preview
• Gaining Teacher Access
• Task Tracker Directions
• Conceptual Physics Course
• On-Level Physics Course
• Honors Physics Course
• Chemistry Concept Builders
• All Chemistry Resources
• Users Voice
• Tasks and Classes
• Webinars and Trainings
• Subscription
• Subscription Locator
• 1-D Kinematics
• Newton's Laws
• Vectors - Motion and Forces in Two Dimensions
• Momentum and Its Conservation
• Work and Energy
• Circular Motion and Satellite Motion
• Thermal Physics
• Static Electricity
• Electric Circuits
• Vibrations and Waves
• Sound Waves and Music
• Light and Color
• Reflection and Mirrors
• Measurement and Calculations
• Elements, Atoms, and Ions
• Compounds,Names, and Formulas
• About the Physics Interactives
• Task Tracker
• Usage Policy
• Newtons Laws
• Vectors and Projectiles
• Forces in 2D
• Momentum and Collisions
• Circular and Satellite Motion
• Balance and Rotation
• Electromagnetism
• Waves and Sound
• Atomic Physics
• Forces in Two Dimensions
• Work, Energy, and Power
• Circular Motion and Gravitation
• Sound Waves
• 1-Dimensional Kinematics
• Circular, Satellite, and Rotational Motion
• Einstein's Theory of Special Relativity
• Waves, Sound and Light
• QuickTime Movies
• About the Concept Builders
• Pricing For Schools
• Directions for Version 2
• Measurement and Units
• Relationships and Graphs
• Rotation and Balance
• Vibrational Motion
• Reflection and Refraction
• Teacher Accounts
• Kinematic Concepts
• Kinematic Graphing
• Wave Motion
• Sound and Music
• About CalcPad
• 1D Kinematics
• Vectors and Forces in 2D
• Simple Harmonic Motion
• Rotational Kinematics
• Rotation and Torque
• Rotational Dynamics
• Electric Fields, Potential, and Capacitance
• Transient RC Circuits
• Light Waves
• Units and Measurement
• Stoichiometry
• Molarity and Solutions
• Thermal Chemistry
• Acids and Bases
• Kinetics and Equilibrium
• Solution Equilibria
• Oxidation-Reduction
• Nuclear Chemistry
• Newton's Laws of Motion
• Work and Energy Packet
• Static Electricity Review
• NGSS Alignments
• 1D-Kinematics
• Projectiles
• Circular Motion
• Magnetism and Electromagnetism
• Graphing Practice
• About the ACT
• ACT Preparation
• For Teachers
• Other Resources
• Solutions Guide
• Solutions Guide Digital Download
• Motion in One Dimension
• Work, Energy and Power
• Chemistry of Matter
• Measurement and the Metric System
• Names and Formulas
• Algebra Based On-Level Physics
• Honors Physics
• Conceptual Physics
• Other Tools
• Frequently Asked Questions
• Purchasing the Download
• Purchasing the Digital Download
• About the NGSS Corner
• NGSS Search
• Force and Motion DCIs - High School
• Energy DCIs - High School
• Wave Applications DCIs - High School
• Force and Motion PEs - High School
• Energy PEs - High School
• Wave Applications PEs - High School
• Crosscutting Concepts
• The Practices
• Physics Topics
• NGSS Corner: Activity List
• NGSS Corner: Infographics
• About the Toolkits
• Position-Velocity-Acceleration
• Position-Time Graphs
• Velocity-Time Graphs
• Newton's First Law
• Newton's Second Law
• Newton's Third Law
• Terminal Velocity
• Projectile Motion
• Forces in 2 Dimensions
• Impulse and Momentum Change
• Momentum Conservation
• Work-Energy Fundamentals
• Work-Energy Relationship
• Roller Coaster Physics
• Satellite Motion
• Electric Fields
• Circuit Concepts
• Series Circuits
• Parallel Circuits
• Describing-Waves
• Wave Behavior Toolkit
• Standing Wave Patterns
• Resonating Air Columns
• Wave Model of Light
• Plane Mirrors
• Curved Mirrors
• Teacher Guide
• Using Lab Notebooks
• Current Electricity
• Light Waves and Color
• Reflection and Ray Model of Light
• Refraction and Ray Model of Light
• Teacher Resources
• Subscriptions

• Newton's Laws
• Einstein's Theory of Special Relativity
• About Concept Checkers
• School Pricing
• Newton's Laws of Motion
• Newton's First Law
• Newton's Third Law
• Sound is a Pressure Wave
• Sound is a Mechanical Wave
• Sound is a Longitudinal Wave

Compressions and Rarefactions

A vibrating tuning fork is capable of creating such a longitudinal wave. As the tines of the fork vibrate back and forth, they push on neighboring air particles. The forward motion of a tine pushes air molecules horizontally to the right and the backward retraction of the tine creates a low-pressure area allowing the air particles to move back to the left.

Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart. These regions are known as compressions and rarefactions respectively. The compressions are regions of high air pressure while the rarefactions are regions of low air pressure. The diagram below depicts a sound wave created by a tuning fork and propagated through the air in an open tube. The compressions and rarefactions are labeled.

The wavelength of a wave is merely the distance that a disturbance travels along the medium in one complete wave cycle. Since a wave repeats its pattern once every wave cycle, the wavelength is sometimes referred to as the length of the repeating patterns - the length of one complete wave. For a transverse wave, this length is commonly measured from one wave crest to the next adjacent wave crest or from one wave trough to the next adjacent wave trough. Since a longitudinal wave does not contain crests and troughs, its wavelength must be measured differently. A longitudinal wave consists of a repeating pattern of compressions and rarefactions. Thus, the wavelength is commonly measured as the distance from one compression to the next adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.

What is a Pressure Wave?

Since a sound wave consists of a repeating pattern of high-pressure and low-pressure regions moving through a medium, it is sometimes referred to as a pressure wave . If a detector, whether it is the human ear or a man-made instrument, were used to detect a sound wave, it would detect fluctuations in pressure as the sound wave impinges upon the detecting device. At one instant in time, the detector would detect a high pressure; this would correspond to the arrival of a compression at the detector site. At the next instant in time, the detector might detect normal pressure. And then finally a low pressure would be detected, corresponding to the arrival of a rarefaction at the detector site. The fluctuations in pressure as detected by the detector occur at periodic and regular time intervals. In fact, a plot of pressure versus time would appear as a sine curve. The peak points of the sine curve correspond to compressions; the low points correspond to rarefactions; and the "zero points" correspond to the pressure that the air would have if there were no disturbance moving through it. The diagram below depicts the correspondence between the longitudinal nature of a sound wave in air and the pressure-time fluctuations that it creates at a fixed detector location.

The above diagram can be somewhat misleading if you are not careful. The representation of sound by a sine wave is merely an attempt to illustrate the sinusoidal nature of the pressure-time fluctuations. Do not conclude that sound is a transverse wave that has crests and troughs. Sound waves traveling through air are indeed longitudinal waves with compressions and rarefactions. As sound passes through air (or any fluid medium), the particles of air do not vibrate in a transverse manner. Do not be misled - sound waves traveling through air are longitudinal waves.

We Would Like to Suggest ...

Check Your Understanding

1. A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound

a. is more dense than air and thus has more inertia, causing the bunching up of sound. b. waves have a speed that is dependent only upon the properties of the medium. c. is like all waves; it is able to bend into the regions of space behind obstacles. d. is able to reflect off fixed ends and interfere with incident waves e. vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations.

Since the particles of the medium vibrate in a longitudinal fashion, compressions and rarefactions are created. Study the tuning fork animation provided on the Tutorial page.

• Pitch and Frequency

How Does Sound Travel Through Air? Complete Explanation

It’s hard to imagine the world without any sound since we rely on it so much. It’s the first thing we hear in the morning, whether it’s the birds or your alarm clock. The sound is everything around us – when people talk, when we watch TV or listen to music, etc. It might also be the last thing you hear before you fall asleep if your neighbor is loud or the dogs are barking.

How does sound travel?

It’s an impressive thing, and though the question seems simple, the answer to it is quite complicated. In the simplest words, the sound is an energy created by vibrations.

However, there’s much more to it so make sure to continue reading. We’ll talk about what the sound is, how it travels, what does it go through the best and much more.

It’s an impressive thing, and though the question seems simple, the answer to it is quite complicated. In the simplest words, the sound is an energy created by vibrations. However, there’s much more to it so make sure to continue reading. We’ll talk about what the sound is, how it travels, what does it go through the best and much more.

Interference

What exactly is sound.

We’re talking about energy produced by vibration. Think about what happens when you hit a drum. Its skin vibrates so quickly forcing the air to vibrate. The air then moves and carries the energy everywhere around the drum.

The physical process of sound is what produces and sends it through the air. The psychological process is what happens in our brain and ears. It converts the energy into what we then call noise, music, speech, etc.

The sound, much like light, comes from its source. The difference is that sound can’t travel through a vacuum. It has to move through something like glass, air, water, metal, etc.

The science behind sound

Interestingly, sound, light, and water behave similarly. Have you ever noticed how beach waves are never the same? Some are larger while others have more power. This is because the energy that carries them is often at different levels.

The same thing happens with sound and light as well. Have you ever tried reflecting light off a mirror? In a similar way, you can also reflect vibration which is something we know as an echo. Echo is the energy that travels to the wall before it bounces back and to your ears. We all know echo doesn’t happen right after the sound as it takes time for the energy to travel.

One thing you have to remember is that these waves lose their energy. This is why you can only hear so far and on calm weather days. If the winds are too strong, you probably won’t hear the noisy club in the other street although you hear it well when the weather is calm. This is because the wind dissipates the energy.

Sound characteristics

Its speed mostly depends on the ambient conditions and the density of the medium. The medium can be thin or thick which will then determines how fast the energy will travel through it. The frequency is the total number of vibrations produced by the source.

Sound waves that have long wavelengths are those we know as low-pitch. Those with short wavelengths are what we know as high-pitch.

How is sound created?

Every physical object causes vibrations when it moves in the air. This leads to creation of waves in the air that then continue to travel as a form of sound.

Much like the drum example we’ve mentioned above, our vocal cords also vibrate when we talk. This vibration happens in air, solid mediums and liquid. These vibrations can travel long distance which is what happens with trains on steel railroad. You know how you can hear the train approaching even when it’s still far away? It’s the vibration.

How do sound waves travel?

Vibrations travel through air at a speed of 343 m/s at room temperature. This goes up to 1482 m/s through water and 5960 m/s through steel. If it’s gaseous medium, the sound will go slowly because the molecules are loosely bound.

They have to travel a long distance in which case they often collide with other molecules. When it’s a solid medium, the atoms are much tightly packed, so the they travel fast. If the medium is liquid, the fragments won’t be as strongly linked, so the waves won’t move as quickly as they do through solid mediums.

The speed of sound

Have you ever heard of someone saying that an airplane broke through the sound barrier? Do you know what that means?

It means that the plane went so fast that it overtook these high-intensity waves it produces. The airplane then makes a sound called a sonic boom. This is why its sound comes to you before you ever see a plane up in the sky.

There’s no one way to tell how quickly it travels. It all depends on the medium since it moves at different speed trough liquid, solid, and gas medium. Its speed depends on how dense is the medium.

The noise travels through steel about 15 times faster than through air and about 4 times faster through water than through air. This is precisely why submarines use SONAR and why it’s nearly impossible to tell where the noise is coming from if you’re swimming in the sea.

Sound also travels differently through different gases. If the air is warm, it will travel much faster than in cold air. It also moves 3x faster in helium than in ordinary air. You know the funny voices you talk in when you breathe in helium? This happens because the waves travel faster and in higher frequency.

How do we hear sound?

We hear with our ears in a seemingly simple process that’s actually quite complex. The impressive organ allows us to hear all kinds of sounds at different frequencies and distances.

The waves travel from the outer ear and through the auditory canal. This causes the eardrum to vibrate which then causes the ossicles to move. The vibrations move with the oval window through the fluid in the inner ear which then stimulates many tiny hair cells. As a result, the vibrations transform into an electrical impulse that our brain perceives as sound.

How does sound travel through a liquid?

Sound always travels in waves regardless of whether it goes through a gas, liquid or a solid medium. They move by particles that collide with one another. It’s a domino effect as one particle hits another much in the same way that the heat travels as well.

The waves don’t go at a rigid pattern in space when it comes to traveling through a liquid. The bond between molecules is usually much weaker, and it keeps breaking and re-forming. Once the pressure is raised at least a little bit, the liquid causes the particles to move to areas with lower pressure. These molecules then push those that are already there causing the pressure to grow in the area.

Molecules have inertia, so they usually go farther than it takes to even out the pressure. The process repeats until the waves carry the energy away. The best example of this are the multiple waves that spread out from where you drop a rock in the water.

How does sound travel through gas?

Gases react much like the liquids. Since they are less dense, gases are more compressible. Sound travels faster when the materials are less dense and more compressed. The compressibility change has a more significant effect on the wave than when the density changes.

In conclusion, the sound travels much slower through gas than through liquids even when it’s the same substance.

Why do different instruments produce different sounds?

If you ever thought about what sound is and how it travels, you probably also thought about music instruments. They are all essentially the same thing, producing sound waves with the same frequency and amplitude. So how they sound different?

Most people think how waves are identical, but the instruments vibrate differently from one another. However, the truth is that the waves aren’t identical. Every instrument produces lots and lots of different waves at the same time. The fundamental wave is the basic one and the one that has a specific amplitude and pitch. Higher-pitched sounds are harmonics also known as overtones. Every overtone has a frequency that’s higher than the fundamental.

This means that every instrument makes a pattern of fundamental frequencies and overtones called timbre. The combination of these waves gives a shape to produce a unique sound of each instrument. That’s precisely why each instrument is different.

There’s another reason and is that the amplitude of each wave changes uniquely every second. A flute produces quick sounds that die soon, while piano vibrations die slowly as they also take longer to build up.

The sound is always reflected from a particular surface at the same angle it strikes it. This allows us to focus sound with curved reflections the same way we use curved mirrors to focus light.

You must’ve heard of whispering galleries, the rooms where you can whisper a word at one point that can then be heard at another point quite far away. We use reflection to focus sound when talking through cupped hands and a megaphone.

However, reflection can be a severe problem in auditoriums and concert halls. If a hall isn’t designed the right way, the first word someone says in the microphone can echo for seconds. If they continue to talk, each word would then echo creating a whole mess. This happens with music just as well.

The issue is usually solved with sound-absorbing materials used to cover the reflecting surfaces. Acoustical tile, draperies, cloths, and many other materials can help. They are all porous allowing waves to enter through the small air-filled spaces and bounce in them until the energy is spent.

Interestingly, some animals also use sound reflection for echolocation. They rely on hearing instead of the sense of sight. Animals such as toothed whales and bats can emit sounds that are beyond our hearing limits and high as 200,000 Hz. Bats can even hear and locate a mosquito even if it’s in total darkness.

When a wave goes from one material to another at a certain angle, it always changes speed. This causes the wavefront to bend and is called refraction.

The best way to understand it is in a physics lab where they use a lens-shaped balloon, fill it with carbon dioxide and focus the sound wave.

Diffraction

When waves go through or around a barrier, the edge of it then becomes a secondary sound source that sends waves of the equally wavelength and frequency.

These waves then spread around, and we call that diffraction. This is a fun phenomenon because it allows us to hear sounds around corners even though sound waves actually travel in a straight line.

Interference occurs each time waves interact. In auditoriums, the interference between the sounds can create dead spots in which clarity and volume are poor. However, it can improve an auditorium’s acoustics if you arrange the reflecting surfaces, so the sound level is increased where the audience sits.

When the two waves that interfere have different frequencies, they create a tone of alternately decreasing and increasing intensity. The pulsations we then hear are called beats. This can be used to your advantage and is something piano turners do all the time. They adjust the tone of a string against a standard tuning fork until you can no longer hear the beat.

How do we use sound?

The sound has a huge part in our lives and is something we rely on every day. Animals probably depend on it even more as they use it for survival. They exchange sounds to communicate or scare off possible threats and different predators.

People have developed a bit more, so we use language. However, every language and every word is essentially a sound we use to communicate.

There are many different sound technologies and musical instruments that produce many different sounds. We’ve also developed technologies that allow us to record sounds on MP3, compact discs, memory sticks, etc.

People also use high frequency sounds otherwise known as ultrasound for so many things from cleaning teeth to checking the baby inside a womb.

NOTIFICATIONS

Sound on the move.

• + Create new collection

Sound is a pressure wave, but this wave behaves slightly differently through air as compared to water. Water is denser than air, so it takes more energy to generate a wave, but once a wave has started, it will travel faster than it would do in air.

A relay race

Sound travels by particles bumping into each other as they vibrate. It is a little like a relay race – each runner holds a little bit of information (the baton), and when they make contact with the next runner, they pass the information on.

In the case of sound, the runners are particles and the information (baton) they are passing along is energy of vibration. In a sound wave, a particle picks up some energy and keeps it until it bumps into a neighbouring particle. The next particle will then pick up the energy and transfer it to the next one in the chain. This happens extremely fast and is detected as a wave of pressure.

Sound won’t travel in a vacuum because there are no particles to bump together to transmit the vibration.

Sound in air

In a gas like air, the particles are generally far apart so they travel further before they bump into one another. There is not much resistance to movement so it doesn’t take much to start a wave, but it won’t travel as fast.

Sound in water

In water, the particles are much closer together, and they can quickly transmit vibration energy from one particle to the next. This means that the sound wave travels over four times faster than it would in air, but it takes a lot of energy to start the vibration. A faint sound in air wouldn’t be transmitted in water as the wave wouldn’t have enough energy to force the water particles to move.

Sound in solids

In a solid, the particles are even closer together and linked by chemical bonds so the wave travels even faster than it does in either liquid or air, but you need quite a lot of energy to start the wave at the beginning.

Sound and temperature

Temperature has a marked influence on the speed of sound. This is not due to a change in how closely together the particles are to each other but relates to the amount of energy that each particle has. Hot particles have more energy and transmit sound better than cold particles. Water in Antarctica will transmit sound slower than water in the tropics.

Some comparisons for the speed of sound in different materials

Related content.

Explore the science concept related to sound further with these articles:

• Hearing sound – the basics of sound waves
• Measuring sound – the different parts of a sound wave, how we talk about and measure sound
• Sound – visualising sound waves – helps students to 'see’ sound waves with videos and diagrams

In our recorded PLD session Sounds of Aotearoa a group of primary science educators introduce some fun ways you can learn and teach about sound.

Activity ideas

Use these activities to explore some essential physics ideas relating to sound, but in a whole new way.

• Modelling waves with slinkies – stay indoors and model how sound travels.
• Catching worms using ground sounds – go outdoors and investigate whether there is any evidence that earthworms respond to vibrations in the ground.
• Sound detectives – can you locate sounds while blindfolded?
• Make and use a hydrophone – and listen to underwater sounds.
• Sound on an oscilloscope – use oscilloscope software and your computer to make and watch a visual sound display.
• Investigating sound – simple exploratory activities and questions to experience and build an understanding of sound.
• Hearing sounds – using whispers and vibrations to hear and experience how sound moves.
• Hearing sounds under water – go underwater yourselves to listen to sounds
• Measuring the speed of sound – use a timing app to measure the speed of sound.

See our newsletters here .

Would you like to take a short survey?

This survey will open in a new tab and you can fill it out after your visit to the site.

Forces of Flight

On this page.

Waves in the Air

What happens as an airplane nears the speed of sound.

As an airplane approaches the speed of sound, conditions around it begin to change. The air ahead of it starts to compress. Shock waves form on its wings and drag increases dramatically.

Shock wave formation in front of the Bell X-1, the first airplane to fly faster than sound; the Concorde, a supersonic airliner; and the Space Shuttle during reentry into the atmosphere.

An Airplane Creates a Wave of Pressure in the Air

A moving airplane causes a disturbance in the air—a wave of pressure—similar to a sound wave. Just like sound waves, any object in motion, such as an airplane, causes a chain reaction of colliding air molecules to spread outward in all directions at the speed of sound. Keep in mind that it is the wave that travels; the air simply moves back and forth. This wave of molecular collisions is called a pressure wave .

What Is Sound?

Sound consists of waves transmitted through the air (or another substance) by molecules bumping into each other. When these sound waves reach your ear, they cause your ear drums to vibrate. Your brain “decodes” the vibrations into voices, music, and noises.

What Is a Sonic Boom?

The shock waves created by an airplane flying faster than sound are nearly cone shaped and extend outward until they dissipate. However, if the airplane is flying low enough so the shock wave reaches the ground, anyone in the shock wave's path will experience a sonic boom . The sound is caused by a sudden, momentary change in air pressure that the ear registers as a loud bang.

What Is a “Mach Number”?

We use Mach numbers to describe an airplane’s speed in terms of the speed of sound.

A Mach number is derived by comparing the speed of an airplane with the speed of sound in the air it’s moving through. An airplane moving at Mach 1 is traveling at the speed of sound. The Mach number is named in honor of Ernst Mach, a late 19th century physicist who studied gas dynamics.

Ranges of Speed

• Subsonic: Usually less than Mach 0.8. Air is flowing slower than sound over every part of the airplane.
• Transonic: About Mach 0.8 to Mach 1.2. Air is flowing faster than sound over some parts of the airplane.
• Supersonic: Greater than about Mach 1.2. Air is flowing faster than sound over the entire airplane.
• Hypersonic: Greater than about Mach 5. Heat becomes a critical factor.

Sonic Booms

Speed of Sound

Ask an explainer, why does sound move faster in warmer air.

WATCH A VIDEO

Supersonic Flight

Find out how a whip and a Slinky can help us understand the speed of sound.

Did You KNOW

The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

The movement of sound through a medium (like air) is affected by:

• Temperature
• All of the above

The movement of sound through a medium is affected by temperature, density and pressure.  Since temperature, density and pressure all decrease with altitude, the speed of sound slows down the higher up you get.

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic & molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids & bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals & rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants & mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition & subtraction addition & subtraction, sciencing_icons_multiplication & division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations & expressions equations & expressions, sciencing_icons_ratios & proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents & logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

• Share Tweet Email Print
• Home ⋅
• Science ⋅
• Physics ⋅
• Sound & Light (Physics): How are They Different?

How Do Sound Waves Travel?

Sound: Definition, Types, Characteristics & Frequencies

In physics, a wave is a disturbance that travels through a medium such as air or water, and moves energy from one place to another. Sound waves, as the name implies, bear a form of energy that our biological sensory equipment -- i.e., our ears and brains -- recognize as noise, be it the pleasant sound of music or the grating cacophony of a jackhammer.

Basic Properties

Sound waves have several features in common with other waves. One is that they must have a substrate, or medium, in which to travel; some are more suitable than others. A second is that they must have a source -- say, the plucking of a guitar string or two hands clapping together. A third is that they transmit energy through direct particle-to-particle interaction, which means that they are a type of mechanical wave.

Sound waves can travel through any material, but not in a vacuum, which is why there is no sound in outer space. The speed of sound in air is about 330 m/s, meaning that it covers a mile in about five seconds. Sound actually travels at far quicker speeds in other media; for example, in biological tissues, it moves at 1,540 m/s.

Related Articles

How to calculate photons per second, properties of infrared light, infrared vs. visible light, differences between protozoa & protists, how is light transmitted, what is the formula for velocity of a wave, how does light travel, how to calculate hertz to joules, how does a transducer work, how does water affect sound, type of energy produced by photosynthesis, how to convert metric tons to cubic yards, how to convert nanometers to joules, the trophic levels of the barn owl, how to calculate frequency.

• The Physics Classroom: Sound Is a Mechanical Wave
• The Physics Hypertextbook: The Nature of Sound

About the Author

Michael Crystal earned a Bachelor of Science in biology at Case Western Reserve University, where he was a varsity distance runner, and is a USA Track and Field-certified coach. Formerly the editor of his running club's newsletter, he has been published in "Trail Runner Magazine" and "Men's Health." He is pursuing a medical degree.

Photo Credits

John Kelly/iStock/Getty Images

Find Your Next Great Science Fair Project! GO

Anatomy of an Electromagnetic Wave

Energy, a measure of the ability to do work, comes in many forms and can transform from one type to another. Examples of stored or potential energy include batteries and water behind a dam. Objects in motion are examples of kinetic energy. Charged particles—such as electrons and protons—create electromagnetic fields when they move, and these fields transport the type of energy we call electromagnetic radiation, or light.

What are Electromagnetic and Mechanical waves?

Mechanical waves and electromagnetic waves are two important ways that energy is transported in the world around us. Waves in water and sound waves in air are two examples of mechanical waves. Mechanical waves are caused by a disturbance or vibration in matter, whether solid, gas, liquid, or plasma. Matter that waves are traveling through is called a medium. Water waves are formed by vibrations in a liquid and sound waves are formed by vibrations in a gas (air). These mechanical waves travel through a medium by causing the molecules to bump into each other, like falling dominoes transferring energy from one to the next. Sound waves cannot travel in the vacuum of space because there is no medium to transmit these mechanical waves.

ELECTROMAGNETIC WAVES

Electricity can be static, like the energy that can make your hair stand on end. Magnetism can also be static, as it is in a refrigerator magnet. A changing magnetic field will induce a changing electric field and vice-versa—the two are linked. These changing fields form electromagnetic waves. Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.

In the 1860's and 1870's, a Scottish scientist named James Clerk Maxwell developed a scientific theory to explain electromagnetic waves. He noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves. He summarized this relationship between electricity and magnetism into what are now referred to as "Maxwell's Equations."

Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. The unit of frequency of a radio wave -- one cycle per second -- is named the hertz, in honor of Heinrich Hertz.

His experiment with radio waves solved two problems. First, he had demonstrated in the concrete, what Maxwell had only theorized — that the velocity of radio waves was equal to the velocity of light! This proved that radio waves were a form of light! Second, Hertz found out how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves — electromagnetic waves.

WAVES OR PARTICLES? YES!

Light is made of discrete packets of energy called photons. Photons carry momentum, have no mass, and travel at the speed of light. All light has both particle-like and wave-like properties. How an instrument is designed to sense the light influences which of these properties are observed. An instrument that diffracts light into a spectrum for analysis is an example of observing the wave-like property of light. The particle-like nature of light is observed by detectors used in digital cameras—individual photons liberate electrons that are used for the detection and storage of the image data.

POLARIZATION

One of the physical properties of light is that it can be polarized. Polarization is a measurement of the electromagnetic field's alignment. In the figure above, the electric field (in red) is vertically polarized. Think of a throwing a Frisbee at a picket fence. In one orientation it will pass through, in another it will be rejected. This is similar to how sunglasses are able to eliminate glare by absorbing the polarized portion of the light.

DESCRIBING ELECTROMAGNETIC ENERGY

The terms light, electromagnetic waves, and radiation all refer to the same physical phenomenon: electromagnetic energy. This energy can be described by frequency, wavelength, or energy. All three are related mathematically such that if you know one, you can calculate the other two. Radio and microwaves are usually described in terms of frequency (Hertz), infrared and visible light in terms of wavelength (meters), and x-rays and gamma rays in terms of energy (electron volts). This is a scientific convention that allows the convenient use of units that have numbers that are neither too large nor too small.

The number of crests that pass a given point within one second is described as the frequency of the wave. One wave—or cycle—per second is called a Hertz (Hz), after Heinrich Hertz who established the existence of radio waves. A wave with two cycles that pass a point in one second has a frequency of 2 Hz.

Electromagnetic waves have crests and troughs similar to those of ocean waves. The distance between crests is the wavelength. The shortest wavelengths are just fractions of the size of an atom, while the longest wavelengths scientists currently study can be larger than the diameter of our planet!

An electromagnetic wave can also be described in terms of its energy—in units of measure called electron volts (eV). An electron volt is the amount of kinetic energy needed to move an electron through one volt potential. Moving along the spectrum from long to short wavelengths, energy increases as the wavelength shortens. Consider a jump rope with its ends being pulled up and down. More energy is needed to make the rope have more waves.

Next: Wave Behaviors

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Anatomy of an Electromagnetic Wave. Retrieved [insert date - e.g. August 10, 2016] , from NASA Science website: http://science.nasa.gov/ems/02_anatomy

Science Mission Directorate. "Anatomy of an Electromagnetic Wave" NASA Science . 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/02_anatomy

Discover More Topics From NASA

James Webb Space Telescope

Perseverance Rover

Parker Solar Probe

• Subscribe to BBC Science Focus Magazine
• Previous Issues
• Future tech
• Everyday science
• Planet Earth
• Newsletters

© Getty Images

How fast does sound travel through water?

Sounds travel faster through water than in air, but it takes more energy to get it going.

Sound is a wave of alternating compression and expansion, so its speed depends on how fast it bounces back from each compression – the less compressible the medium it’s travelling through, the faster it bounces back. Water is about 15,000 times less compressible than air, but it is also 800 times denser. The extra density means that the molecules accelerate more slowly for a given force, which slows the compression wave down. So water’s high density partly offsets its extreme incompressibility and sound travels at 1,493m/s, about four times faster than through air. The speed of sound in diamond is so high because it is extremely incompressible and yet relatively light.

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.

Share this article

• Terms & Conditions
• Privacy policy
• Cookies policy
• Code of conduct
• Magazine subscriptions
• Manage preferences

Professional Development

Exams admin, qualifications.

Centre Services

Art and Design

Computer Science

Design and Technology

Food preparation and Nutrition

Mathematics

Media Studies

Physical Education

Religious Studies

All subjects

Biology (8461)

Chemistry (8462)

Combined Science: Trilogy (8464)

English Language (8700)

English Literature (8702)

Geography (8035)

History (8145)

Mathematics (8300)

See all GCSEs

AS and A-levels

Biology (7401)

Business (7131)

Chemistry (7404)

Geography (7037)

History (7041)

Physics (7407)

Psychology (7181)

Sociology (7191)

See all AS & A Levels

Other qualifications

Applied Generals

AQA Certificate Mathematics

Entry Level Certificates

Project Qualifications

Unit Award Scheme

All qualifications

Our training

Course finder

About our training

Online training

Face-to-face training

Inside assessment

Courses by theme

Effective exam prep

Exams officers

Getting started with AQA

Virtual communities

Courses by subject

All Professional Development

Dates and timetables

Non-exam assessment (NEA)

NEA, coursework and controlled assessment

Deadlines for non-exam assessment

Record forms

Submit marks

Exams guidance

Question papers and stationery

Access arrangements

Special consideration

Results days

Results slips

Grade boundaries

Results statistics

Post-results services

Exam certificates

All Exams Admin

Assessment Services

Associate Extranet

Become an associate

All About Maths

Stride Maths

News & Insights

AQI research & insight

Inside exams podcast

GCSE Physics 8463

GCSE Physics Specification Specification for first teaching in 2016

PDF | 1.95 MB

Wave behaviour is common in both natural and man-made systems. Waves carry energy from one place to another and can also carry information. Designing comfortable and safe structures such as bridges, houses and music performance halls requires an understanding of mechanical waves. Modern technologies such as imaging and communication systems show how we can make the most of electromagnetic waves.

4.6.1 Waves in air, fluids and solids

4.6.1.1 transverse and longitudinal waves, 4.6.1.2 properties of waves.

Required practical activity 8: make observations to identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid and take appropriate measurements.

AT skills covered by this practical activity: AT 4.

This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development .

4.6.1.3 Reflection of waves (physics only)

Required practical activity 9 (physics only): investigate the reflection of light by different types of surface and the refraction of light by different substances.

AT skills covered by this practical activity: AT 4 and 8.

4.6.1.4 Sound waves (physics only) (HT only)

4.6.1.5 waves for detection and exploration (physics only) (ht only), 4.6.2 electromagnetic waves, 4.6.2.1 types of electromagnetic waves, 4.6.2.2 properties of electromagnetic waves 1.

Required practical activity 10 : investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.

AT skills covered by this practical activity: AT 1 and 4.

4.6.2.3 Properties of electromagnetic waves 2

4.6.2.4 uses and applications of electromagnetic waves, 4.6.2.5 lenses (physics only), 4.6.2.6 visible light (physics only), 4.6.3 black body radiation (physics only), 4.6.3.1 emission and absorption of infrared radiation, 4.6.3.2 perfect black bodies and radiation.