50 Fun Facts About Waves (Physics)

Which Japanese word meaning "harbor wave" names the giant ocean waves set off by undersea earthquakes?

Tsunami joins the Japanese words for harbor and wave. Far out at sea one can slip under a ship almost unnoticed, then rear up as it reaches shallow water near the coast.

A cork bobs up and down as ripples pass instead of drifting along, because waves transfer what rather than matter?

Energy is what a wave moves from place to place, while the material it passes through never strays far from where it started. Waves also carry momentum and information.

Which phenomenon, named after an Austrian physicist, makes an ambulance siren sound lower once it has passed?

The Doppler effect carries the name of Christian Doppler, who proposed it in 1842 to explain the colors of double stars rather than sound.

A singer can shatter a wine glass by holding a note at the glass's natural frequency, an example of what?

Resonance makes a vibration grow when each push arrives in time with an object's natural rhythm. A playground swing climbs higher for the same reason when every shove is timed to its swing.

A jet flying faster than sound drags a cone-shaped shock wave behind it that people on the ground hear as what?

A sonic boom is not a one-off bang made at the moment a plane breaks the sound barrier. It follows the aircraft for the whole supersonic flight, sweeping a strip of ground known as the boom carpet.

A wall must stand at least about 17 meters away before a listener can hear which effect as a separate sound?

An echo from any closer returns less than a tenth of a second after the shout, too soon for the ear to tell the two apart. In Greek myth, Echo was a nymph cursed to repeat only the last words spoken to her.

Which type of sunglasses cuts road glare by blocking light waves that vibrate in the horizontal direction?

Polarized lenses block the side-to-side vibration that dominates glare bouncing off a wet road or a lake. One test for a pair is to look through two at once, with one turned a quarter turn against the other.

Which Austrian physicist, famous for a thought experiment about a cat, wrote the wave equation of quantum theory?

Erwin Schrödinger worked on the equation during a Christmas 1925 retreat in the Swiss Alps and published it the next year. It led to his Nobel Prize in Physics in 1933.

Which ripples in spacetime, predicted by Albert Einstein, were first detected in 2015 from two colliding black holes?

Gravitational waves are so faint that Einstein himself doubted they could ever be detected. The 2015 signal had been traveling for more than a billion years when it reached Earth.

Which name is given to the highest point of a wave, the part that overturns when a wave breaks on a beach?

The crest grows steeper as a wave runs up a sloping seabed until it becomes unstable and spills forward. Whitewater tumbling down the front of the wave is the result.

A sailor measures wave height from the top of a wave straight down to which lowest point?

The trough is the bottom of the dip between two waves, so a wave's height is counted from there to the top. That makes it double the wave's rise above calm water.

A wave's speed equals its frequency multiplied by which distance, measured from one peak to the next?

Wavelength is usually written with the Greek letter lambda. At a fixed speed it shrinks as the frequency climbs, so the faster a wave vibrates, the more tightly packed its peaks are.

The A in AM radio stands for which wave property, the one linked to how loud a sound is?

Amplitude is the size of a wave's swing away from its rest position, and an AM station varies it to carry speech and music. AM was the earliest method used to broadcast audio by radio.

The unit of frequency, one cycle per second, honors which German physicist who first proved radio waves exist?

Heinrich Hertz saw no use for the invisible waves he produced in his laboratory. Asked what his discovery might be good for, he replied, "Nothing, I guess."

The time a wave takes to complete one full cycle, equal to one divided by its frequency, is called what?

Period is the flip side of frequency. A heart beating 120 times a minute, or twice a second, has one of half a second.

Tightening a guitar string raises the frequency of the sound wave it makes, which raises which quality of the note?

Pitch is the ear's reading of frequency, so faster vibrations sound higher. Human hearing runs from about 20 vibrations a second up to about 20,000, and the upper limit falls with age.

Sound and ocean waves both need a material to travel through, which places them in which class of wave?

Mechanical waves are vibrations of matter itself, which is why no sound can cross the emptiness of space. Light needs no such carrier and reaches Earth from the Sun through a vacuum.

In a transverse wave, such as a ripple sent along a rope, the rope moves which way relative to the wave's travel?

At right angles is the rule for every transverse wave, light included: the vibration runs across the line of travel. Flick one end of a tied rope up and down and the hump runs along it while the rope only rises and falls.

Sound in air squeezes and stretches the air along its direction of travel, which makes it which type of wave?

Longitudinal waves shake a material back and forth along the line of travel instead of across it. Sound in air is one, a train of pressure pulses moving at about 343 meters per second.

A pen dipped in water looks bent at the surface because of which wave behavior, caused by light changing speed?

Refraction happens because light slows as it passes from air into water, and a wave that changes speed at an angle swings onto a new heading. Camera lenses and the human eye both use it to steer light.

Which wave behavior, named by the Italian scientist Francesco Grimaldi, lets a shout be heard from behind a tree?

Diffraction is the spreading of waves around an obstacle or through a gap. Grimaldi coined the word from the Latin for breaking into pieces, after watching light fan out in different directions.

Noise-cancelling headphones kill a hum by playing its mirror image, so the two sounds cancel through which process?

Interference is what happens whenever two waves overlap and add together. The headphones play a copy of the noise flipped upside down, so each peak meets a dip and the two wipe each other out.

The law of reflection says a mirror throws light back at an angle equal to the angle of what?

Incidence means the arrival of the incoming ray. Both angles are measured from the normal, an imaginary line drawn straight out from the mirror's surface.

Which cables carry internet data as pulses of light, kept inside the glass by total internal reflection?

Optical fibers are strands of glass about as thick as a human hair. Light inside strikes the wall at too shallow an angle to escape, so it bounces along the core instead of leaking out.

Light bending through layers of hot air above a desert road creates which illusion of a shimmering pool of water?

A mirage is a real effect of light rather than a hallucination, so a camera can capture it. The "water" on a hot road is in fact a displaced image of the sky.

Isaac Newton showed that white sunlight is a mix of colors by passing a beam through which piece of glass?

A prism bends each color by a different angle, fanning white light into a spectrum, a word Newton himself chose. He then merged the colors back into white with a lens and a second one.

Light passing straight through a clear window, rather than bouncing off or soaking in, shows which wave behavior?

Transmission is one of three fates for light striking a surface, alongside bouncing off and being soaked up. Plate glass and clean water let most light through, which is what makes them transparent.

Which technology, first developed to hunt submarines, finds underwater objects by timing reflected pulses of sound?

Sonar is short for sound navigation and ranging. Navies had a working system by 1918, built to answer the submarine threat of World War I.

A plucked guitar string vibrates in loops between its two fixed ends, forming which kind of wave?

Standing waves form when a wave and its returning twin overlap, here running between the two ends of the string. Franz Melde coined the term around 1860 after experiments with vibrating strings.

Which electromagnetic waves, given off by radioactive atoms, sit at the high-frequency end of the spectrum?

Gamma rays pass through most materials so easily that shielding takes dense lead or concrete. Paul Villard discovered them in 1900 while studying the radiation given off by radium.

A TV remote sends its commands as pulses of which invisible electromagnetic waves, discovered with a thermometer?

Infrared turned up in 1800 when the astronomer William Herschel split sunlight and found the temperature kept rising beyond the red end. Slightly more than half of the Sun's output reaches Earth in this form.

Which Scottish physicist worked out in the 1860s that light is an electromagnetic wave, decades before radio existed?

James Clerk Maxwell showed that electric and magnetic fields travel through space as waves at the speed of light. He also presented the first durable color photograph, in 1861.

Which English polymath made the case for light as a wave in 1801 with an experiment built around two slits?

Thomas Young saw the light spread into bright and dark bands, a pattern that overlapping waves make and streams of particles should not. He was also instrumental in deciphering the Rosetta Stone.

Which Dutch scientist, inventor of the pendulum clock, told the Paris Academy in 1678 that light travels as a wave?

Christiaan Huygens published the idea in 1690 as his Treatise on Light, picturing light as a series of spreading wave fronts. As an astronomer he also discovered Titan, the largest moon of Saturn.

Light travels as a wave, yet Albert Einstein proposed in 1905 that it also comes in tiny packets called what?

Photons were Einstein's way of explaining the photoelectric effect, work that won him the 1921 Nobel Prize in Physics. The name itself came later, popularized by the chemist Gilbert Lewis in 1926.

Which invisible substance was once thought to fill space and carry light, until an 1887 experiment failed to find it?

The aether was imagined as doing for light what air does for sound, and its full name, luminiferous, means light-bearing. The experiment that found no trace of it was run by Albert Michelson and Edward Morley.

Which French aristocrat proposed in his 1924 doctoral thesis that electrons, and all matter, have wave properties?

Louis de Broglie was proved right in 1927, when experiments confirmed that matter really does behave like a wave. The Nobel Prize in Physics followed two years later.

Light from galaxies racing away from Earth arrives stretched to lower frequencies, an effect astronomers call what?

Redshift grows with distance, as Edwin Hubble reported in 1929: the farther away a galaxy lies, the more its light is stretched. The rule is now called Hubble's law.

Which Italian inventor reported in 1901 that he had picked up a radio signal sent across the Atlantic Ocean?

Guglielmo Marconi said he heard the Morse code letter S, sent from Cornwall, on an antenna held aloft by a kite in Newfoundland. He went on to share the 1909 Nobel Prize in Physics.

Sound waves cross which of these materials almost fifteen times faster than they cross air?

Iron carries sound at about 5,120 meters per second, against 343 in air. As a rule sound moves slowest through gases, faster through liquids and fastest through solids.

Which sound waves, too high in frequency for humans to hear, do bats and porpoises use to locate their prey?

Ultrasound begins above the top of human hearing. Lazzaro Spallanzani showed in the 1790s that bats can find their way without sight, long before anyone could detect their high-pitched calls.

Most waves on the open ocean are raised by which force of nature dragging across the water's surface?

The wind sets their size by its speed, by how long it blows and by the stretch of open water it crosses, known as the fetch. Once they leave the storm that raised them they travel on as swell, sometimes for thousands of kilometers.

Which instrument records the ground's shaking as earthquake waves arrive, tracing the motion as a wavy line?

A seismograph is a motion sensor joined to a timer and a recorder. The earliest well-documented earthquake detector was built in China by Zhang Heng in AD 132.

On a vibrating guitar string, which name is given to the points that stay perfectly still, such as its two fixed ends?

Nodes are where the string does not move at all, while the points of widest swing between them are antinodes. Pressing a string against a fret shifts the end one, which shortens the vibrating length and changes the note.

Doubling the frequency of a musical note raises it by which interval, the gap from one C to the next?

An octave joins two notes alike enough to share the same letter name. Go up one from a note at 440 vibrations a second and you reach 880; go down one and you reach 220.

In a sound wave, the regions where air molecules are squeezed closest together are known as what?

Compressions are bands of slightly raised pressure, which is why sound is also described as a pressure wave. They alternate with stretched-out bands of lower pressure as the wave moves along.

In a sound wave, the stretched-out regions where air pressure dips below normal take which name?

Rarefactions are the opposite of a squeeze: patches where the air is thinner than normal. Mountain air is rarefied in the same sense, less dense than the air lower down.

Two notes of almost the same frequency played together produce a slow pulsing in volume that musicians call what?

Beats slow down as two notes are brought closer together and fade out when they match. Musicians listen for that pulsing when matching one instrument to another.

Which coiled-spring toy, invented by a naval engineer in 1943, is stretched out in classrooms to show how waves travel?

A Slinky makes a wave visible: push one end and bunched-up coils run along the spring while each coil stays near home. Its inventor got the idea from watching a spring step down off a shelf.

Which American suspension bridge, nicknamed Galloping Gertie for its heaving deck, tore itself apart in 1940?

Tacoma Narrows Bridge lasted just four months, and the only death in the collapse was a cocker spaniel named Tubby. Textbooks long blamed vibration building in step with the gusts, but engineers point to aeroelastic flutter.