A sound's pitch will seem to change if the listener or the source moves toward or away from the other because motion changes the time it takes each successive sound wave to reach the listener.

Relative motion between a source and an observer shifts the color of observed light

The phenomenon, known as the Doppler effect, is the result of experiencing an increase in the frequency of observed waves when approaching a source and a decrease when moving away. Because this property corresponds to color, approaching objects appear bluer than normal—blueshift—and receding objects appear redder than usual—redshift.

If a source of music traveled past someone at twice the speed of sound, assuming sufficiently sensitive hearing and powerful equipment, they would hear the music backward.

By analyzing the color of starlight, astronomers can determine how fast stars within a galaxy are moving toward or away from Earth, revealing the expansion rate of the universe.

View a collection of sound animations, which depict how a source of sound waves pushes against particles to carry energy away without matter being displaced.

Interacting sound waves can create regions where the pressure from each wave combines, allowing objects to levitate in place against gravity or be manipulated for touch-free construction.

Sonar, or sound navigation and ranging, uses reflected sound waves to map and detect seafloor features, marine organisms, and other obstacles.

Objects that move faster than the speed of sound—Mach 1—create shockwaves called sonic booms by building up and forcing sound waves to combine as they lag behind the object.

Ultrasound machines emit and receive high-frequency sound waves to construct images of the body's interior, with differences in the penetrating power of different frequencies allowing medical professionals to identify different structures.

The three smallest bones in the human body—the malleus, incus, and stapes—amplify the vibrations of sound waves by almost 20 times to help enable hearing.

A person's voice sounds different when breathing helium, sulfur hexafluoride, or gases other than air because the speed of sound varies with the properties of the material through which it travels.

Some animals possess sensitive hearing to help pinpoint prey and map the world

Bats and dolphins produce sound to reflect off surfaces and create a mental image of their surroundings. Owls' faces are dish-shaped to help funnel sounds to their ears, including that of mice moving along leaves or snow. Pinnipeds, such as seals and walruses, hear in both air and water.

Explore a visual and auditory guide to wave properties and waveforms to learn how every sound imaginable can be created by combining multiple vibrations of air.

Listen to the 'sounds' of the universe with this sonification library, where astronomers have transformed certain astronomical data sets into audio for broader engagement.

Vertigo is a mismatch of information between the eyes and the ears

Both vertigo and motion sickness can be caused by mismatches between visual and auditory inputs.The brain relies on inputs from the eyes, inner ear, and receptors in muscles and joints to orient the body. When the eyes suggest movement but other signals suggest the body is stationary dizziness and nausea can occur.

We hear because soundwaves are converted into electrochemical signals in our ears

This science teacher video systematically walks through the biology of the outer, middle, and inner ear. The explanation starts with the auricle, an external part that funnels sound through the auditory canal, and the tympanic membrane (the ear drum), which vibrates when sounds hit it. Beyond that, as the video details, is the eustachian tube, which is connected to the back of our throats and allows air to pass in and out to equalize ear pressure.

When struck, objects vibrate at unique rates called resonant frequencies, which makes tapping wood sound different from tapping metal, but providing objects with sound at their resonant frequency can cause them to shatter.

When GPS and sonar are unavailable, submarine navigation relies on a fiber-optic gyroscope to determine the vessel's orientation and an accelerometer to calculate distance traveled.

Studying 'sonic' black holes

If a fish screams as it falls down a cascading waterfall accelerating to ridiculous speeds, will his fish friends above hear him scream? This analogy, odd as it is, has become an essential tool in the astrophysicists kit for learning how enigmatic black holes operate. Lab experiments mirroring the so-called sonic black hole have achieved insights for their cosmic counterparts. Read how it works in this brief piece.

If hearing is damaged, the brain may amplify remaining sounds, perhaps causing tinnitus.

Try out an online tone generator, which produces sounds of specific frequencies to help tune instruments, test your hearing, and generate beats by overlapping tones.

Just as light bends at different angles as it travels through different materials, seismic waves move in different directions through Earth's interior, revealing the presence of layers with varying properties.

Listen to the sounds of pulsars, which emit radio pulses up to hundreds of times a second

Just as figure skaters spin faster by tucking in their arms, these celestial objects acquire high rates of spin from the collapse of the cores of massive stars. The star's rotation spins its magnetic field, generating beams of radio waves from its magnetic poles. If either of these poles faces a detector, the signals can be picked up and converted to audio signals.

Listen to the pair of colliding black holes detected by LIGO

As ripples in spacetime, gravitational waves do not produce sound, which is the perception of specific vibrations in matter (e.g., vocal cords vibrating air molecules). The "chirp" of gravitational waves comes instead from converting the spacetime ripples into sound waves that the human ear can hear.

Pulsatile tinnitus is when you hear thumping synchronized with your heartbeat

This rare type of tinnitus, which sounds like rhythmic thumping or whooshing, is often linked to blood vessel conditions or high blood pressure. Lowering blood pressure through exercise and food choices can help reduce the severity of this condition.

By measuring radio signals transmitted to and received from distant spacecraft, NASA's Deep Space Network can determine a spacecraft's position and speed and send commands to alter its trajectory.

Watch the motion of an individual photon using a high-speed camera

Although light travels over 3 million football fields per second, cameras that capture trillions of frames per second can observe individual particles of light as they interact with atoms in materials they travel through. Such observations can be used to determine the speed of light in different materials.

The finite speed of light means we can only perceive the world's past

When objects emit or reflect light, it takes time for the light to reach an observer and be detected. During the travel time, the object may have changed, limiting detections to describing the conditions of the object when the light was first emitted or reflected, before it was detected.

You may be better at spotting a lie when listening to a speaker's voice inflections rather than watching for facial and body cues.

Listen to samples of 'sounds' produced in the sun's interior, created from the sonification of internal vibrations detected by the Parker Solar Probe.

According to the special theory of relativity, the faster objects move through space, the less they move through time, and therefore age more slowly.

Create flute, saxophone, trumpet, or violin reproductions of any 15-second piece of audio using machine learning.

Why you may hate the sound of your voice

It's a relatively common experience to cringe while listening to a recording of your own voice. This Popular Science article offers physiological explanations for the discrepancy between what we hear when we speak versus what others hear. The piece also expands on the psychology behind this discontent, and how our voices influence our self-perception and social interactions.

The physics behind opera singing

How can opera singers project their voices to audiences in huge auditoriums without using microphones and overpowering the orchestra? This video explains this phenomenon, using animation to demonstrate the physics of the human voice and how opera singers hone their technique to hit higher frequencies and a distinctive ringing timbre known as their squillo.

The mass of a cell can be measured using hollow, vibrating beams

In 2010, scientists at MIT constructed a U-shaped device that vibrates like a guitar string with an internal fluid channel. As cells and bacteria pass through the device, its rate of vibration shifts, with greater mass creating larger shifts.

The bullwhip was the first human-made object to break the sound barrier, producing a small sonic boom heard as a crack when flicked quickly.

Light appears to slow down as it travels through different materials

As electromagnetic waves interact with particles in a transparent medium, particles vibrate and generate their own electromagnetic waves. The interference of the original and generated waves, which are slightly delayed, results in ensemble light with an effective slower speed but unchanged color.

The underlying fabric of the universe—spacetime—changes shape in the presence of mass and energy, which affects measurements of space and time.

Noise-canceling headphones use a microphone to identify external sounds, which are then used to produce an out-of-sync version of those sounds to cancel them in your ears.

In television and film, certain sounds, such as dialogue, may be difficult to understand due to sound mixing, device limitations, and technological advancements that have collectively reduced clarity.

Age-related hearing loss, known as presbycusis, is a top cause of hearing loss

This video walks through the biology of why presbycusis (prez-buh-kyoo-sis) occurs and its etiology. This type of hearing loss is gradual and typically starts with reductions in the ability to hear high-pitched sounds.

As the universe expands, the color of light shifts as it travels through space

As space stretches out, the wavelength of light traveling through it also expands, causing its frequency to decrease to maintain the speed of light constant. Since we perceive frequency as color, a lower frequency would produce a redder color, allowing astronomers to correlate reddening with the rate of expansion.

LIGO boosts its signal sensitivity by manipulating quantum uncertainty

According to the uncertainty principle, the amplitude, or height of a wave's peak, and its phase—the point in time when the first peak is observed—are inversely linked. Based on the frequency of the gravitational waves of interest, scientists sacrifice precision in one optical property to reduce noise in another.

Within quantum mechanics, the Heisenberg uncertainty principle limits how precisely one can simultaneously know the values of pairs of complementary properties for an object, such as position and momentum.

Hurricanes spin due to differences in air and ground speed as they move across Earth

The movement of an object across latitudes causes it to take a curved trajectory because its speed no longer matches that of the ground beneath it. This phenomenon, called the Coriolis effect, explains why hurricanes spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Stonehenge may have functioned as an echo chamber designed to keep ceremonies secret from outsiders.

Acoustics researcher Trevor Cox discovered that Stonehenge acts like a concert hall, reflecting and amplifying sound. This video shows Cox demonstrating the effect using a scale model inside a soundproof studio.

50 years of research has focused on unraveling the relationship between music and frisson

One insight reveals that musical passages with surprising volume changes or unexpected harmonies and beauty are more likely to trigger frisson, perhaps because they upend listeners' expectations.

What did Ötzi the Iceman sound like?

The natural pitch of a person's voice depends on the size of their larynx, also known as their voice box, and the length and thickness of their vocal folds or vocal cords. Using this information, scientists have recreated the voice of Ötzi the...

Try to catch the 'sound' of black holes in gravitational wave detector data

In "Black Hole Hunter," users try to listen for gravitational wave signals from black holes in four sample data files that include substantial background noise. With each level, learn more about black holes while being faced with ever-quieter signals.

According to the special theory of relativity, because the passage of time depends on how quickly objects move through space, people will not agree on the order of events they observe if they are moving at different speeds.

Mapping hearing loss in the US

Nearly 10% of Americans suffer from some degree of hearing loss, measured as the inability to hear sounds lower than 25 decibels. The incidence of hearing loss increases with age and is typically higher among men. Recent analysis produced a puzzling observation researchers can't quite explain: There's a larger incidence of hearing loss among rural populations than in urban centers. Explore the data with this map and explainer.