does sound travel faster than light

• Speed Of Sound vs Speed Of Light

The speed of sound and the speed of light are two common concepts that most of us likely learn about at some point in life. Both are defined rather simply, with the speed of sound being the speed that sound travels, and the speed of light being the speed at which light travels. Although these two concepts may sound similar, they are in fact radically different from one another. What are some of the differences between them?

The first notable difference between the speed of sound and light is how fast they are. In Earth’s atmosphere , the speed of sound averages at about 761-miles per hour (1,225-kilometres per hour). That may seem fast, yet when compared to the speed of light, it seems quite small. Light travels at a staggering 670-million miles per hour (1.07-billion kilometres per hour). That’s around 880,000 times faster than the speed of sound. 

Sound Must Have A Medium

In order for sound to exist, it must have a medium to travel through. For sound, this medium is air, and that’s why sound does not exist in the emptiness of space. Meanwhile, light does not need a medium to exist. Rather, light travels independently of any medium, and thus it can travel through space, unlike sound. 

The Speed Of Light Is Constant

Another notable difference between light and sound is that the speed of light is constant while the speed of sound is not. Since the speed of sound requires air to exist, its speed is dependent upon the density and temperature of air. For example, when we say that sound travels at 761-miles per hour, this is only the case at sea level and when temperatures are around 59-degrees Fahrenheit (15-degrees Celsius). If you are at a higher elevation where the density of air is lower and temperatures are colder, the speed of sound will be different. Thus, the speed of sound varies. Light, however, has no such constraint. Rather, the speed of light is constant regardless of any other factor. No matter the conditions, it always travels at the same speed. 

Things That Can Move Faster Than Sound

The speed of sound is fast, yet it is by no means the fastest thing in the universe. It is not even the fastest thing on Earth . Human’s have broken the sound barrier countless times, a speed known as supersonic speed. Light is a different story, however. The speed of light is a fixed law of nature, and it represents the fastest possible speed anything can move at. No matter how hard we try or how advanced technology becomes, the current understanding of the cosmos is that the light barrier cannot be broken. Thus, the speed of light is like a cosmic speed limit. 

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Why does light travel faster than sound?

Asked by: Toby Graham, Shrewsbury

Robert Matthews

According to Einstein's Special Relativity, the speed of light has a unique status: it's a fundamental feature of our Universe, representing the maximum speed at which information can travel from place to place. As such, nothing can match the 300,000km/s achieved by light travelling through a vacuum – least of all sound, which being waves of compression and expansion in a substance doesn’t even exist in a vacuum.

That said, light can be slowed down by being passed through transparent materials – by around 33 per cent in the case of glass. Even so, it still zooms through glass around 50,000 times faster than sound waves.

• Does the speed of light ever change?
• What would you see if you could travel at the speed of light?
• How fast does sound travel through water?
• Does sound travel further on foggy days?

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The Science Site

Common entrance science revision.

Light and Sound

• The Earth in Space
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Light and sound are made of WAVES. They are both forms of ENERGY.

Light travels much faster than sound. This is why the flash of lightening is seen long before the sound of thunder is heard, even though they are formed at the same instant.

Speed of light 3×10 10 m/s (300,000 km/s) Speed of sound 330m/s

Light Light is given out from a luminous source eg the sun or a projector lamp.

Light travels in straight lines.

In order to see anything light has to be reflected off of it and enter our eye.

Shadows are formed when RAYS of light are stopped by an object that does not TRANSMIT light.

When light hits some coloured paper (eg a red book) some colours are absorbed but the red light is scattered which is why the book looks red.

Words you need to know from this topic REFLECTION When light bounces off a smooth surface (eg a mirror) and forms an image behind it.

REFRACTION When light gets bent by passing from air into water or glass (or passing back again).

ABSORPTION When light hits an object and does not get reflected back (eg when light hits a piece of black paper it is absorbed, this is why the paper looks black)

TRANSMISSION When light passes straight through something like a piece of transparent paper.

DISPERSION The splitting of white light into a SPECTRUM. This is often done by a using a PRISM

FIBRE OPTICS: Optical fibres are strands of thin glass. Light can bounce from one end of the strand and come out of the other.

They are used in communications where they are now used to carry telephone or computer messages instead of wires.

Some ray diagrams

Sound        

In order to produce a sound something has to vibrate .

The vibrating object causes compressions in the air which in turn cause the ear drum in our ear to vibrate.

The frequency of the vibrations determine the pitch of the note: Faster vibrations produce a note with a higher pitch.

The size (amplitude) of the vibrations determine the volume of the sound: If the amplitude increases then the sound will get louder .

Sound travels faster in solids and liquids than it does in air.

Sound will NOT travel through a vacuum.

How sound is produced in different musical instruments

instrument part which vibrates instrument part which vibrates

Trumpet: Lips Organ: Air

Clarinet: Reed Guitar: Strings

Piano: Strings Drum: drum skin

Echoes An echo is heard when sound is reflected off a distant object.

Sonar make use of echoes to measure the distance (or shape) of an object (eg the sea floor).

It does this by measuring the length of time it takes to hear the echo.

Ultrasound Ultra sound is too high for us to hear (maybe about 40kHz). It is used to produce pictures of unborn babies,

in burglar alarms and also in some cleaning devices

Words to know:

Frequency: the number of vibrations per second.

Pitch: how high or low a note sounds.

Amplitude: the height of a wave

Volume: How loud a note is.

If the frequency increases then the pitch will increase. If the amplitude increases then the volume will increase.

Some waveforms

17.2 Speed of Sound, Frequency, and Wavelength

Learning objectives.

By the end of this section, you will be able to:

• Define pitch.
• Describe the relationship between the speed of sound, its frequency, and its wavelength.
• Describe the effects on the speed of sound as it travels through various media.
• Describe the effects of temperature on the speed of sound.

Sound, like all waves, travels at a certain speed and has the properties of frequency and wavelength. You can observe direct evidence of the speed of sound while watching a fireworks display. The flash of an explosion is seen well before its sound is heard, implying both that sound travels at a finite speed and that it is much slower than light. You can also directly sense the frequency of a sound. Perception of frequency is called pitch . The wavelength of sound is not directly sensed, but indirect evidence is found in the correlation of the size of musical instruments with their pitch. Small instruments, such as a piccolo, typically make high-pitch sounds, while large instruments, such as a tuba, typically make low-pitch sounds. High pitch means small wavelength, and the size of a musical instrument is directly related to the wavelengths of sound it produces. So a small instrument creates short-wavelength sounds. Similar arguments hold that a large instrument creates long-wavelength sounds.

The relationship of the speed of sound, its frequency, and wavelength is the same as for all waves:

where v w v w is the speed of sound, f f is its frequency, and λ λ is its wavelength. The wavelength of a sound is the distance between adjacent identical parts of a wave—for example, between adjacent compressions as illustrated in Figure 17.8 . The frequency is the same as that of the source and is the number of waves that pass a point per unit time.

Table 17.1 makes it apparent that the speed of sound varies greatly in different media. The speed of sound in a medium is determined by a combination of the medium’s rigidity (or compressibility in gases) and its density. The more rigid (or less compressible) the medium, the faster the speed of sound. For materials that have similar rigidities, sound will travel faster through the one with the lower density because the sound energy is more easily transferred from particle to particle. The speed of sound in air is low, because air is compressible. Because liquids and solids are relatively rigid and very difficult to compress, the speed of sound in such media is generally greater than in gases.

Earthquakes, essentially sound waves in Earth’s crust, are an interesting example of how the speed of sound depends on the rigidity of the medium. Earthquakes have both longitudinal and transverse components, and these travel at different speeds. The bulk modulus of granite is greater than its shear modulus. For that reason, the speed of longitudinal or pressure waves (P-waves) in earthquakes in granite is significantly higher than the speed of transverse or shear waves (S-waves). Both components of earthquakes travel slower in less rigid material, such as sediments. P-waves have speeds of 4 to 7 km/s, and S-waves correspondingly range in speed from 2 to 5 km/s, both being faster in more rigid material. The P-wave gets progressively farther ahead of the S-wave as they travel through Earth’s crust. The time between the P- and S-waves is routinely used to determine the distance to their source, the epicenter of the earthquake. The time and nature of these wave differences also provides the evidence for the nature of Earth's core. Through careful analysis of seismographic records of large earthquakes whose waves could be clearly detected around the world, Richard Dixon Oldham established that waves passing through the center of the Earth behaved as if they were moving through a different medium: a liquid. Later on, Inge Lehmann used more precise observations (partly based on a better coordinated network of seismographs she helped set up) to better define the nature of the core: that it was a solid inner core surrounded by a liquid outer core.

The speed of sound is affected by temperature in a given medium. For air at sea level, the speed of sound is given by

where the temperature (denoted as T T ) is in units of kelvin. The speed of sound in gases is related to the average speed of particles in the gas, v rms v rms , and that

where k k is the Boltzmann constant ( 1.38 × 10 −23 J/K 1.38 × 10 −23 J/K ) and m m is the mass of each (identical) particle in the gas. So, it is reasonable that the speed of sound in air and other gases should depend on the square root of temperature. While not negligible, this is not a strong dependence. At 0ºC 0ºC , the speed of sound is 331 m/s, whereas at 20.0ºC 20.0ºC it is 343 m/s, less than a 4% increase. Figure 17.9 shows a use of the speed of sound by a bat to sense distances. Echoes are also used in medical imaging.

One of the more important properties of sound is that its speed is nearly independent of frequency. This independence is certainly true in open air for sounds in the audible range of 20 to 20,000 Hz. If this independence were not true, you would certainly notice it for music played by a marching band in a football stadium, for example. Suppose that high-frequency sounds traveled faster—then the farther you were from the band, the more the sound from the low-pitch instruments would lag that from the high-pitch ones. But the music from all instruments arrives in cadence independent of distance, and so all frequencies must travel at nearly the same speed. Recall that

In a given medium under fixed conditions, v w v w is constant, so that there is a relationship between f f and λ λ ; the higher the frequency, the smaller the wavelength. See Figure 17.10 and consider the following example.

Example 17.1

Calculating wavelengths: what are the wavelengths of audible sounds.

Calculate the wavelengths of sounds at the extremes of the audible range, 20 and 20,000 Hz, in 30.0ºC 30.0ºC air. (Assume that the frequency values are accurate to two significant figures.)

To find wavelength from frequency, we can use v w = fλ v w = fλ .

• Identify knowns. The value for v w v w , is given by v w = 331 m/s T 273 K . v w = 331 m/s T 273 K . 17.5
• Convert the temperature into kelvin and then enter the temperature into the equation v w = 331 m/s 303 K 273 K = 348 . 7 m/s . v w = 331 m/s 303 K 273 K = 348 . 7 m/s . 17.6
• Solve the relationship between speed and wavelength for λ λ : λ = v w f . λ = v w f . 17.7
• Enter the speed and the minimum frequency to give the maximum wavelength: λ max = 348 . 7 m/s 20 Hz = 17 m . λ max = 348 . 7 m/s 20 Hz = 17 m . 17.8
• Enter the speed and the maximum frequency to give the minimum wavelength: λ min = 348 . 7 m/s 20 , 000 Hz = 0 . 017 m = 1 . 7 cm . λ min = 348 . 7 m/s 20 , 000 Hz = 0 . 017 m = 1 . 7 cm . 17.9

Because the product of f f multiplied by λ λ equals a constant, the smaller f f is, the larger λ λ must be, and vice versa.

The speed of sound can change when sound travels from one medium to another. However, the frequency usually remains the same because it is like a driven oscillation and has the frequency of the original source. If v w v w changes and f f remains the same, then the wavelength λ λ must change. That is, because v w = fλ v w = fλ , the higher the speed of a sound, the greater its wavelength for a given frequency.

Making Connections: Take-Home Investigation—Voice as a Sound Wave

Suspend a sheet of paper so that the top edge of the paper is fixed and the bottom edge is free to move. You could tape the top edge of the paper to the edge of a table. Gently blow near the edge of the bottom of the sheet and note how the sheet moves. Speak softly and then louder such that the sounds hit the edge of the bottom of the paper, and note how the sheet moves. Explain the effects.

Check Your Understanding

Imagine you observe two fireworks explode. You hear the explosion of one as soon as you see it. However, you see the other firework for several milliseconds before you hear the explosion. Explain why this is so.

Sound and light both travel at definite speeds. The speed of sound is slower than the speed of light. The first firework is probably very close by, so the speed difference is not noticeable. The second firework is farther away, so the light arrives at your eyes noticeably sooner than the sound wave arrives at your ears.

You observe two musical instruments that you cannot identify. One plays high-pitch sounds and the other plays low-pitch sounds. How could you determine which is which without hearing either of them play?

Compare their sizes. High-pitch instruments are generally smaller than low-pitch instruments because they generate a smaller wavelength.

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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..., 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 .

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Speed of Sound and Light

Most recent answer: 2/14/2017

(published on 10/22/2007)

Follow-Up #1: light/sound time lag

Follow-up #2: light and sound.

(published on 05/16/2013)

Follow-Up #3: The difference in time taken

The time taken to reach a particular distance (in most general sense) depends on how fast someone is moving. The speed of light is much faster than the speed of sound in air. If you want to compare, the speed of sound in air is ~ 343 m/s and the speed of light is 3x10 10 m/s. In other words, light travels 186 thousand miles in 1 second, while sound takes almost 5 seconds to travel 1 mile.

(published on 02/14/2017)

Follow-up on this answer

Related Questions

• How to calculate velocity when you are not given the tim
• Is the speed of sound dependent on frequency?
• Can you transmit information faster than light with solid rods?
• Total Internal Reflection of Light and Sound
• Doppler shift formulas
• Waves in shallow water
• Radio Telescopes and X Ray Telescopes
• Sight and Sound

Still Curious?

Expore Q&As in related categories

• Speed of Sound

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Traveling waves

17 How sound moves

Speed of sound.

There’s a delay between when a sound is created and when it is heard. In everyday life, the delay is usually too short to notice. However, the delay can be noticeable if the distance between source and detector is large enough. You see lightning before you hear the thunder. If you’ve sat in the outfield seats in a baseball stadium, you’ve experienced the delay between seeing the player hit the ball and the sound of the “whack.” Life experiences tell us that sound travels fast, but not nearly as fast as light does. Careful experiments confirm this idea.

The speed of sound in air is roughly 340 m/s. The actual value depends somewhat on the temperature and humidity. In everyday terms, sound travels about the length of three and a half foot ball fields every second- about 50% faster than a Boeing 747 (roughly 250 m/s). This may seem fast, but it’s tiny compared to light, which travels roughly a million times faster than sound (roughly 300,000,000 m/s).

Sound requires some material in which to propagate (i.e. travel). This material sound travels through is called the medium . You can show that sound requires a medium by putting a cell phone inside a glass jar connected to a vacuum pump. As the air is removed from the jar, the cell phone’s ringer gets quieter and quieter. A youTube video (2:05 min) produced by the UNSW PhysClips project shows the demo with a drumming toy monkey [1] instead of a cell phone.

What affects the speed of sound?

Sound travels at different speeds though different materials. The physical properties of the medium are the only factors that affect the speed of sound- nothing else matters.

The speed of sound in a material is determined mainly by two properties- the stiffness of the material and the density of the material. Sound travels fastest through materials that are stiff and light. In general, sound travels fastest through solids, slower through liquids and slowest through gasses. (See the table on this page). This may seem backwards- after all, metals are quite dense. However, the high density of metals is more than offset by far greater stiffness (compared to liquids and solids).

The speed of sound in air depends mainly on temperature. The speed of sound is 331 m/s in dry air at 0 o Celsius and increases slightly with temperature- about 0.6 m/s for every 1 o Celsius for temperatures commonly found on Earth. Though speed of sound in air also depends on humidity, the effect is tiny- sound travels only about 1 m/s faster in air with 100% humidity air at 20 o C than it does in completely dry air at the same temperature.

Nothing else matters

The properties of the medium are the only factors that affect the speed of sound- nothing else matters.

Frequency of the sound does not matter- high frequency sounds travel at the same speed as low frequency sounds. If you’ve ever listened to music, you’ve witnessed this-  the low notes and the high notes that were made simultaneously reach you simultaneously, even if you are far from the stage. If you’ve heard someone shout from across a field, you’ve noticed that the entire shout sound (which contains many different frequencies at once) reaches you at the same time. If different frequencies traveled at different rates, some frequencies would arrive before others.

The amplitude of the sound does not matter- loud sounds and quiet ones travel at the same speed. Whisper or yell- it doesn’t matter. The sound still takes the same amount of time to reach the listener.  You’ve probably heard that you can figure out how far away the lightning by counting the seconds between when you see lightning and hear thunder. If the speed of sound depended on loudness, this rule of thumb would have to account for loudness- yet there is nothing in the rule about loud vs. quiet thunder. The rule of thumb works the same for all thunder- regardless of loudness . That’s because the speed of sound doesn’t depend on amplitude.

Stop to thinks

• Which takes longer to cross a football field: the sound of a high pitched chirp emitted by a fruit bat or the (relatively) low pitched sound emitted by a trumpet?
• Which sound takes longer to travel 100 meters: the sound of a snapping twig in the forest or the sound of a gunshot?
• Which takes longer to travel the distance of a football field: the low pitched sound of a whale or the somewhat higher pitched sound of a human being?

Constant speed

Sound travels at a constant speed. Sound does not speed up or slow down as it travels (unless the properties of the material the sound is going through changes). I know what you’re thinking- how is that possible? Sounds die out as they travel, right? True. That means sounds must slow down and come to a stop, right? Wrong. As sound travels, its amplitude decreases- but that’s not the same thing as slowing down. Sound (in air) covers roughly 340 meters each and every second, even as its amplitude shrinks. Eventually, the amplitude gets small enough that the sound is undetectable. A sound’s amplitude shrinks as it travels, but its speed remains constant.

The basic equation for constant speed motion (shown below) applies to sound.

[latex]d=vt[/latex]

In this equation, [latex]d[/latex] represents the distance traveled by the sound, [latex]t[/latex] represents the amount of time it took to go that distance and [latex]v[/latex] represents the speed.

Rule of thumb for lightning example

Example: thunder and lightning.

The rule of thumb for figuring out how far away a lightning strike is from you is this:

Count the number of seconds between when you see the lightning and hear the thunder. Divide the number of seconds by five to find out how many miles away the lightning hit.

According to this rule, what is the speed of sound in air? How does the speed of sound implied by this rule compare to 340 m/s?

Identify important physics concept :   This question is about speed of sound.

List known and unknown quantities (with letter names and units):

At first glance, it doesn’t look like there’s enough information to solve the problem. We were asked to find speed, but not given either a time or a distance. However, the problem does allow us to figure out a distance if we know the time- “Divide the number of seconds by five to find out how many miles away the lightning hit.” So, let’s make up a time and see what happens; if the time is 10 seconds, the rule of thumb says that the distance should be 2 miles.

[latex]v= \: ?[/latex]

[latex]d=2 \: miles[/latex]

[latex]t=10 \: seconds[/latex]

You might ask “Is making stuff up OK here?” The answer is YES! If the rule of thumb is right, it should work no matter what time we choose. (To check if the rule is OK, we should probably test it with more than just one distance-time combination, but we’ll assume the rule is OK for now).

Do the algebra:  The equation is already solved for speed. Move on to the next step.

Do unit conversions (if needed) then plug in numbers:  If you just plug in the numbers, the speed comes out in miles per second:

[latex]v = \frac{2 \: miles} {10 \: seconds}=0.2 \: \frac{miles} {second}[/latex]

We are asked to compare this speed to 340 m/s, so a unit conversion is in order; since there are 1609 meters in a mile:

[latex]v =0.2 \: \frac{miles} {second}*\frac{1609 \: meters} {1 \:mile}=320 \frac{m}{s}[/latex]

Reflect on the answer:

• The answer for speed from the rule of thumb is less than 10% off the actual value of roughly 340 m/s- surprisingly close!
• At the beginning, we assumed a time of 10 seconds. Does the result hold up for other choices? A quick check shows that it does! For instance, if we use a time of 5 seconds, the rule of thumb gives a distance of 1 mile, and the math still gives a speed of 0.2 miles/second. The speed will be the same no matter what time we pick. The reason is this:  The more time it takes the thunder to arrive, the farther away the lightning strike is, but the speed remains the same. In the equation for speed, both time and distance change by the same factor and the overall fraction remains unchanged.

Stop to think answers

• Both sounds take the same amount of time. (High and low pitched sounds travel at the same speed).
• Both sounds take the same amount of time. (Quiet sounds and loud sounds travel at the same speed).
• The sound of the whale travels the distance in less time- assuming sound from the whale travels in water and sound from the human travels in air. Sound travels faster in water than in air. (The info about frequency was given just to throw you off- frequency doesn’t matter).
• Wolfe, J. (2014, February 20). Properties of Sound. Retrieved from https://www.youtube.com/watch?v=P8-govgAffY ↵

Understanding Sound Copyright © by dsa2gamba and abbottds is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Blue Sky Science: Why is light faster than sound?

Molly Torinus

Why is light faster than sound?

Brandon Walker

Light and sound are very different. Sound is actually a mechanical disturbance through air or another medium. Sound always needs a medium to travel through and the type of medium determines its speed.

Imagine a bunch of molecules bouncing around in the air. If you hit an object or make a fast motion, the molecules that you push are going to hit the ones in front of it. You’ll get this disturbance in the direction of travel of however you made the initial motion, and it will move through the medium. That’s how sound travels—as a pressure wave.

Light, on the other hand, is not a pressure wave—it’s a fundamental particle. One ray of light is typically called a photon, and it’s an electromagnetic disturbance. Light doesn’t need a medium to travel.

The speed of sound through air is about 340 meters per second. It’s faster through water and it’s even faster through steel. Light will travel through a vacuum at 300 million meters per second. So they’re totally different scales.

No information can propagate faster than the speed of light. If you have light that’s going through a media, it can travel slower than that. But the speed of sound and speed of light are totally incomparable.

You normally don’t notice this speed difference on a day-to-day basis. This speed difference does become apparent, for example, with lightning. You’ll always see lightning before you hear it, because typically lightning will be a mile away, two miles away. That’s a great enough distance that that speed difference becomes apparent to your brain.

Sound Always Travels Slower than Light myth

What Travels Faster, Sound or Light?

Sound usually travels slower than light, but not always. Under normal conditions, light moves roughly a million times faster than sound, but under the right conditions sound can travel faster than light.

The reason sound typically travels slower than light is because light naturally travels (in a true vacuum ) at the fastest possible speed information can travel (light speed). Light (AKA electromagnetic energy) and doesn’t require a medium to travel through, while sound must always travel through a medium (traveling at about 332 meters per second through air molecules). With that said, there are a few “cheats” to make the sound go faster than light and faster than light speed (c). [1] [2]

So while we can say light typically travels faster than sound, we can’t say sound always travels slower than light or that sound can’t travel faster than the speed of light. We explain below.

TIP : Learn more about the difference between sound waves and light waves .

FACT : Sound travels faster in solids (about 6,000 meters per second), about half that speed in water, and then of course much slower in a gas like air (about 332 meters per second). The more tightly packed the molecules, the faster the molecules vibrate and the faster sound travels.

FACT : The standard metric for the speed of light is that of light traveling in a vacuum. This physical constant , denoted as “c,” is roughly 186,000 miles per second (or 299,792,458 meters per second). Light speed is roughly one million times the speed of sound in air. Light always moves near light speed (although typically slower as nature abhors a vacuum ), but light can bounce off objects (slowing its linear movement at light speed) and can be slowed in specific situations (such as if it is trapped in a photonic crystal). See Physicists Slow Speed of Light  from 1999, which explains how light can be slowed by a factor of 20 million (thus much slower than sound). [3]

How to Make Sound Travel Faster Than Light

There are a few different ways to make sound travel faster than light, and faster than light speed.

Slowing Down Light

“No thing ” travels faster than light , but sound isn’t a thing, it is a disruption of molecules, and light is a thing, it is electromagnetic energy. Due to this distinction, it is possible to cheat by slowing down light (in say a photonic crystal). If we slow down light, we can shoot some sound off at 340-ish meters per second and have sound technically travel faster than light (but not faster than light speed). [4] [5]

FACT : If a tree falls in the forest, it makes a sound. The laws of physics don’t stop working just because we aren’t around to verify them. Sound is a disruption of molecules and for every action there is an equal and opposite reaction. The tree must make a sound (unless it falls in true empty space).

Utilizing Group Velocity

Oddly, we can also make sound travel faster than light speed by using a setup similar to the one Tennessee State University classroom did in 2007 . [6]

In a normal dispersive medium, the velocity of a wave is proportional to its wavelength, resulting in a group velocity that is slower than the average velocity of its constituent waves. But in an “anomalously” dispersive medium — one that becomes highly absorbing or attenuating at certain frequencies — velocity is inversely proportional to wavelength, meaning that the group velocity can become much faster. –  Sound breaks the light barrier

FACT : Both gravity and sound are “classical waves,” unlike light, which is a quantum wave. Classical waves don’t propagate instantly. Instead, they travel through a medium; thus we “hear” an exploding neutron star after we see it, just like we see a firework before we hear it.

FACT : “In space, no one can hear you scream,” because there is no medium for sound to travel through in space.

• The speed of sound in air
• ‘Mach c’? Scientists observe sound traveling faster than the speed of light
• Sound Pulses Exceed Speed of Light
• Photonic crystal
• Physicists Slow Speed of Light
• Sound breaks the light barrier

The rule is “no thing” (anything comprised of electromagnetic energy, of which all matter is) can travel faster than light speed, but non-things (anything not comprised of electromagnetic energy, like a shadow or sound) can.

Thus, although sound will almost always take longer to propagate than light (and thus, we will always “see the flash” before we “hear the bang”) sound can actually break the light barrier under the right conditions. All this to say, the idea that sound always travels slower than light is oddly a myth.

Thomas DeMichele is the content creator behind ObamaCareFacts.com, FactMyth.com, CryptocurrencyFacts.com, and other DogMediaSolutions.com and Massive Dog properties. He also contributes to MakerDAO and other cryptocurrency-based projects. Tom's focus in all...

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milex Supports this as a Fact.

wow i’m amazed with so much info thx

Norika pizza lover Doesn't beleive this myth.

Thomas DeMichele The Author Did not vote.

Agree, the article agrees. Since light doesn’t always travel faster than sound, the idea that sound always travels slower (or that light always travels faster) is a misconception or myth.

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What is the speed of light? Here’s the history, discovery of the cosmic speed limit

On one hand, the speed of light is just a number: 299,792,458 meters per second. And on the other, it’s one of the most important constants that appears in nature and defines the relationship of causality itself.

As far as we can measure, it is a constant. It is the same speed for every observer in the entire universe. This constancy was first established in the late 1800’s with the experiments of Albert Michelson and Edward Morley at Case Western Reserve University . They attempted to measure changes in the speed of light as the Earth orbited around the Sun. They found no such variation, and no experiment ever since then has either.

Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn’t measurably changed in over 13.8 billion years.

In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light may not be a constant, for all known purposes it is a constant, so it’s better to just define it and move on with life.

How was the speed of light first measured?

In 1676 the Danish astronomer Ole Christensen Romer made the first quantitative measurement of how fast light travels. He carefully observed the orbit of Io, the innermost moon of Jupiter. As the Earth circles the Sun in its own orbit, sometimes it approaches Jupiter and sometimes it recedes away from it. When the Earth is approaching Jupiter, the path that light has to travel from Io is shorter than when the Earth is receding away from Jupiter. By carefully measuring the changes to Io’s orbital period, Romer calculated a speed of light of around 220,000 kilometers per second.

Observations continued to improve until by the 19 th century astronomers and physicists had developed the sophistication to get very close to the modern value. In 1865, James Clerk Maxwell made a remarkable discovery. He was investigating the properties of electricity and magnetism, which for decades had remained mysterious in unconnected laboratory experiments around the world. Maxwell found that electricity and magnetism were really two sides of the same coin, both manifestations of a single electromagnetic force.

As Maxwell explored the consequences of his new theory, he found that changing magnetic fields can lead to changing electric fields, which then lead to a new round of changing magnetic fields. The fields leapfrog over each other and can even travel through empty space. When Maxwell went to calculate the speed of these electromagnetic waves, he was surprised to see the speed of light pop out – the first theoretical calculation of this important number.

What is the most precise measurement of the speed of light?

Because it is defined to be a constant, there’s no need to measure it further. The number we’ve defined is it, with no uncertainty, no error bars. It’s done. But the speed of light is just that – a speed. The number we choose to represent it depends on the units we use: kilometers versus miles, seconds versus hours, and so on. In fact, physicists commonly just set the speed of light to be 1 to make their calculations easier. So instead of trying to measure the speed light travels, physicists turn to more precisely measuring other units, like the length of the meter or the duration of the second. In other words, the defined value of the speed of light is used to establish the length of other units like the meter.

How does light slow down?

Yes, the speed of light is always a constant. But it slows down whenever it travels through a medium like air or water. How does this work? There are a few different ways to present an answer to this question, depending on whether you prefer a particle-like picture or a wave-like picture.

In a particle-like picture, light is made of tiny little bullets called photons. All those photons always travel at the speed of light, but as light passes through a medium those photons get all tangled up, bouncing around among all the molecules of the medium. This slows down the overall propagation of light, because it takes more time for the group of photons to make it through.

In a wave-like picture, light is made of electromagnetic waves. When these waves pass through a medium, they get all the charged particles in motion, which in turn generate new electromagnetic waves of their own. These interfere with the original light, forcing it to slow down as it passes through.

Either way, light always travels at the same speed, but matter can interfere with its travel, making it slow down.

Why is the speed of light important?

The speed of light is important because it’s about way more than, well, the speed of light. In the early 1900’s Einstein realized just how special this speed is. The old physics, dominated by the work of Isaac Newton, said that the universe had a fixed reference frame from which we could measure all motion. This is why Michelson and Morley went looking for changes in the speed, because it should change depending on our point of view. But their experiments showed that the speed was always constant, so what gives?

Einstein decided to take this experiment at face value. He assumed that the speed of light is a true, fundamental constant. No matter where you are, no matter how fast you’re moving, you’ll always see the same speed.

This is wild to think about. If you’re traveling at 99% the speed of light and turn on a flashlight, the beam will race ahead of you at…exactly the speed of light, no more, no less. If you’re coming from the opposite direction, you’ll still also measure the exact same speed.

This constancy forms the basis of Einstein’s special theory of relativity, which tells us that while all motion is relative – different observers won’t always agree on the length of measurements or the duration of events – some things are truly universal, like the speed of light.

Can you go faster than light speed?

Nope. Nothing can. Any particle with zero mass must travel at light speed. But anything with mass (which is most of the universe) cannot. The problem is relativity. The faster you go, the more energy you have. But we know from Einstein’s relativity that energy and mass are the same thing. So the more energy you have, the more mass you have, which makes it harder for you to go even faster. You can get as close as you want to the speed of light, but to actually crack that barrier takes an infinite amount of energy. So don’t even try.

How is the speed at which light travels related to causality?

If you think you can find a cheat to get around the limitations of light speed, then I need to tell you about its role in special relativity. You see, it’s not just about light. It just so happens that light travels at this special speed, and it was the first thing we discovered to travel at this speed. So it could have had another name. Indeed, a better name for this speed might be “the speed of time.”

Related: Is time travel possible? An astrophysicist explains

We live in a universe of causes and effects. All effects are preceded by a cause, and all causes lead to effects. The speed of light limits how quickly causes can lead to effects. Because it’s a maximum speed limit for any motion or interaction, in a given amount of time there’s a limit to what I can influence. If I want to tap you on the shoulder and you’re right next to me, I can do it right away. But if you’re on the other side of the planet, I have to travel there first. The motion of me traveling to you is limited by the speed of light, so that sets how quickly I can tap you on the shoulder – the speed light travels dictates how quickly a single cause can create an effect.

The ability to go faster than light would allow effects to happen before their causes. In essence, time travel into the past would be possible with faster-than-light travel. Since we view time as the unbroken chain of causes and effects going from the past to the future, breaking the speed of light would break causality, which would seriously undermine our sense of the forward motion of time.

Why does light travel at this speed?

No clue. It appears to us as a fundamental constant of nature. We have no theory of physics that explains its existence or why it has the value that it does. We hope that a future understanding of nature will provide this explanation, but right now all investigations are purely theoretical. For now, we just have to take it as a given.

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Sound breaks the light barrier

Nothing can travel faster than light… except for sound. This is the claim of some US physicists, who say they have designed an unusual waveguide to make sound move at “superluminal” speeds ( Appl. Phys. Lett. 90 014102).

Sound often comprises numerous superimposed waves of various wavelengths. At certain points, these constituent waves can all combine constructively to produce a pulse, which moves through the medium at a velocity known as the “group velocity”.

In a normal dispersive medium, the velocity of a wave is proportional to its wavelength, resulting in a group velocity that is slower than the average velocity of its constituent waves. But in an “anomalously” dispersive medium — one that becomes highly absorbing or attenuating at certain frequencies — velocity is inversely proportional to wavelength, meaning that the group velocity can become much faster.

Indeed, the group velocity of light has already been shown to travel faster than the speed of light in a vacuum. But until now, superluminal acoustic waves have existed only in theory, and would require the group velocity to increase almost a million times over.

William Robertson and colleagues from Middle Tennessee State University in the US have managed to produce “faster than light” sound, however, by putting a sound pulse through a surprisingly simple waveguide. Inside, a loop filter splits the signal along two unequal length paths, and then recombines it to produce large amounts of anomalous dispersion. As they interfere with each other, they replicate the shape of the original pulse, only farther ahead. This gives the impression that the sound has travelled farther, and thus faster, in the same space of time.

Robertson says that such split-path interference can also occur naturally when a sound source is located near a hard wall: some of the sound reaches the listener directly, and some reaches the listener from a slightly longer path as it bounces off the wall. Therefore, he says, superluminal sound is an “everyday” occurrence, although it is mostly too subtle to notice.

Proponents of Einstein’s special relativity need not worry, though. The underlying waves that make up the pulse remain at subluminal velocities, so no information, matter or energy actually travels faster than light. (See related link: “Subluminal”.)

“The effect is the same as that observed in previous electrical or optical experiments,” Robertson told Physics Web . “The only somewhat startling difference is that the acoustic waves making up the pulse move so much more slowly than light.”

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January 17, 2007 feature

'Mach c'? Scientists observe sound traveling faster than the speed of light

For the first time, scientists have experimentally demonstrated that sound pulses can travel at velocities faster than the speed of light, c. William Robertson’s team from Middle Tennessee State University also showed that the group velocity of sound waves can become infinite, and even negative.

Past experiments have demonstrated that the group velocities of other materials’ components—such as optical, microwave, and electrical pulses—can exceed the speed of light. But while the individual spectral components of these pulses have velocities very close to c, the components of sound waves are almost six orders of magnitude slower than light (compare 340 m/s to 300,000,000 m/s).

“All of the interest in fast (and slow) wave velocity for all types of waves (optical, electrical, and acoustic) was initially to gain a fundamental understanding of the characteristics of wave propagation,” Robertson told PhysOrg.com . “Phase manipulation can change the phase relationship between these materials’ components. Using sound to create a group velocity that exceeds the speed of light is significant here because it dramatically illustrates this point, due to the large difference between the speeds of sound and light.”

The experiment was conducted by two undergrads, an area high school teacher and two high school students, who received funding by an NSF STEP (Science, technology, engineering, math Talent Enhancement Program) grant. The grant aims to increase recruitment and retention of students to these subjects.

In their experiment, the researchers achieved superluminal sound velocity by rephasing the spectral components of the sound pulses, which later recombine to form an identical-looking part of the pulse much further along within the pulse. So it’s not the actual sound waves that exceed c, but the waves’ “group velocity,” or the “length of the sample divided by the time taken for the peak of a pulse to traverse the sample.”

“The sound-faster-than-light result will not be a surprise to the folks who work closely in this area because they recognize that the group velocity (the velocity that the peak of a pulse moves) is not merely connected to the velocity of all of the frequencies that superpose to create that pulse,” explained Robertson, “but rather to the manner in which a material or a filter changes the phase relationship between these components. By appropriate phase manipulation (rephasing) the group velocity can be increased or decreased.”

To rephase the spectral components, the sound waves were sent through an asymmetric loop filter on a waveguide of PVC pipe, about 8 m long. The 0.65-meter loop split the sound waves into two unequal path lengths, resulting in destructive interference and standing wave resonances that together created transmission dips at regular frequencies.

Due to anomalous dispersion (which changes the wave speed), sound pulses traveling through the loop filter arrived at the exit sooner than pulses traveling straight through the PVC. With this experiment, the group velocity could actually reach an infinitely small amount of time, although the individual spectral components still travel at the speed of sound.

“We also achieved what is known as a ‘negative group velocity,’ a situation in which the peak of the output pulse exits the filter before the peak of the input pulse has reached the beginning of the filter,” explained Robertson. “Using the definition for speed as being equal to distance divided by time, we measured a negative time and thus realized a negative velocity.”

It might not seem that a negative velocity would exceed the speed of light, but in this case, Robertson said, the speed of the pulse is actually much faster than c.

“Consider the pulse speed in a slightly less dramatic case,” Robertson said. “Say the peak of the output pulse exits the filter at exactly the same time as the input pulse reaches the beginning. In this less dramatic case, the transit time is zero and the speed (distance divided by zero) is infinite. So we were beyond infinite! (‘To infinity and beyond,’ to steal a line from Toy Story .) In our experiment, we measured a negative transit time corresponding to a negative group velocity of -52 m/s.”

Although such results may at first appear to violate special relativity (Einstein’s law that no material object can exceed the speed of light), the actual significance of these experiments is a little different. These types of superluminal phenomena, Robertson et al. explain, violate neither causality nor special relativity, nor do they enable information to travel faster than c. In fact, theoretical work had predicted that the superluminal speed of the group velocity of sound waves should exist.

“The key to understanding this seeming paradox is that no wave energy exceeded the speed of light,” said Robertson. “Because we were passing the pulse through a filter, the sped-up pulse was much smaller (by more than a factor of 10) than the input pulse. Essentially, the pulse that made it through the filter was an exact (but smaller) replica of the input pulse. This replica is carved from the leading edge of the input pulse. At all times, the net energy of the wave crossing the filter region was equal to, or less than, the energy that would have arrived if the input pulse had been traveling in a straight pipe instead of through the filter.”

Is this phenomenon simply the result of a clever set-up, or can it actually occur in the real world? According to the scientists, the interference that occurs in the loop filter is directly analogous to the “comb filtering” effect in architectural acoustics, where sound interference occurs between sound directly from a source and that reflected by a hard surface.

“The superluminal acoustic effect we have described is likely a ubiquitous but imperceptible phenomenon in the everyday world,” the scientists conclude.

Citation: Robertson, W., Pappafotis, J., Flannigan, P., Cathey, J., Cathey, B., and Klaus, C. “Sound beyond the speed of light: Measurement of negative group velocity in an acoustic loop filter.” Applied Physics Letters 90, 014102 (2007).

By Lisa Zyga, Copyright 2006 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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The speed of sound on Mars is constantly changing, bizarre study finds

New research shows that the speed of sound on Mars varies considerably by location and temperature. The findings could help scientists understand sounds picked up by Martian rovers, as well as make future crewed ventures safer.

Researchers have teased out the details of how sound behaves at various times and places on Mars — and the results are very different from what we are used to on Earth.

NASA's Perseverance rover on Mars carries several microphones. These devices, intended to study the properties of materials on the Red Planet, have picked up all sorts of additional sounds, including the eerie spluttering of Martian dust devils . 

Recordings have already shown that sound behaves peculiarly on Mars. For instance, noises below 240 hertz — roughly a piano's middle C — travel about 30 feet per second (10 meters per second) slower than higher-pitched sounds do. This is because carbon dioxide molecules, which absorb some of sound's energy at low frequencies, make up 95% of Mars' atmosphere. Such bizarre properties, if unaccounted for, could compromise communications on future Mars missions, particularly crewed ones. 

With this in mind, a team of scientists from French and U.S. institutions set out to study the speed of sound and its attenuation — its tendency to die down over distance — within the first 60 feet (20 m) of Mars' atmosphere. 

To begin, the team collated values of different parameters — including atmospheric pressure, temperature and chemical composition — at various spots on the Red Planet from the Mars Climate Database . Changes in these parameters can stretch or shrink sound waves, making these factors essential in predicting sound's properties. 

Related: Soar through the 'Labyrinth of Night' — a Martian canyon the size of Italy — in thrilling new satellite video

The team calculated sound speed and attenuation at different points of time in the planet's year (which is about 687 Earth days) and in various spots across the Martian landscape, including mountain peaks and valleys. This approach was necessary because the underlying factors vary massively over space and time.  In the polar regions, for example, midday temperatures can fluctuate by 108 degrees Fahrenheit (60 degrees Celsius), and carbon dioxide levels by 30%, across seasons. 

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The calculations turned up several interesting findings, which were published May 7 in the JGR: Planets . For one, dust doesn't seem to affect sound propagation, the authors said in a joint email to Live Science — similar to on Earth, where a dust storm between you and an airport, for example, wouldn't obstruct your ability to hear the planes taking off. The change in the speed of sound with temperature (about 0.5 m/s for every degree Celsius) is also similar to that on Earth.

Unlike on Earth, though, sound speed and attenuation depend greatly on carbon dioxide levels. Additionally, while the speed of sound rises abruptly at around 240 hertz, the extent of the shift is less pronounced at lower temperatures than at higher ones.

The biggest difference from Earth, though, stems from the enormous fluctuations in temperature — and, to a lesser extent, the concentration of carbon dioxide — daily. In the area where the Perseverance rover currently dwells, for instance, mercury levels change by about 90 degrees Fahrenheit (50 degrees Celsius) during the day. This causes sound to travel up to 100 feet per second (30 m/s) and die down three times faster in the hotter hours compared with the colder ones. Changes in temperature and carbon dioxide levels also cause variation in sound speed and attenuation across seasons, although this effect is more pronounced in the polar regions. 

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The results allow scientists to "predict the sound speed and attenuation for any location at the Martian surface at any time of year and any time of day," the researchers told Live Science. The model can also improve scientists' understanding of what sound-producing objects on Mars actually sound like. 

"We only hear it [a sound] after the sound has propagated through the atmosphere," the authors said. "Our model can help to retrieve the characteristics of the original sound sources." 

Additionally, the model provides a glimpse of life for future human residents on Mars: Mornings on mountaintops may be the closest thing to the way sound behaves on Earth. At other times and places, like afternoons at the Perseverance site, a jarring effect will occur as high-pitched noises at close distances reach the ears faster than lower-pitched ones; more distant noises ordinarily audible on Earth won't be heard at all.

Deepa Jain is a freelance science writer from Bengaluru, India. Her educational background consists of a master's degree in biology from the Indian Institute of Science, Bengaluru, and an almost-completed bachelor's degree in archaeology from the University of Leicester, UK. She enjoys writing about astronomy, the natural world and archaeology. 

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