Physics 20 Questions

Sound waves transport energy from one place to another. Sounds are waves produced by vibrations of matter. The original vibration stimulates the vibration of something larger or more massive. This vibrating material then sends a disturbance through the surrounding medium, ex. air, as longitudinal waves.

*Pitch* is the human perception of sound frequency. Our subjective impression about the frequency of sound is pitch. *Frequency* corresponds to pitch. A high-pitched sound has high frequency; a low pitch sound has a low frequency.

20 to 20,000 hertz. As humans age, this hearing range shrinks, especially at the high-frequency end.

*Infrasonic* is too low in frequency (below 20 Hz) for humans to hear, whereas *ultrasonic* is too high (above 20,000 Hz).

220 Hz.

Relative to solids and liquids, air is a poor conductor of sound. Any elastic substance, solid liquid gas plasma, can transmit sound. Inelastic substances (putty) cannot transmit sound. The speed of sound is generally greater in solids than in liquids, and greater in liquids than in gases.

There is no material in a vacuum to vibrate and carry the sound. Vacuums do not transmit sound since there is nothing to compress or expand.

In a compression, the molecules are closer together than average; in a rarefaction, they are further apart.

They travel in the same direction at the same speed.

It depends on wind conditions, temperature and humidity, not on loudness and frequency. All sounds in the same medium travel at the same speed.

340 m/s

Faster in warm air, faster in humid air. Water vapor in the air increases the speed slightly. Faster moving molecules in warm air bump into each other more often and transmit a pulse in less time.

They travel in the same direction, same speed, as shown in Fig. 20.1

Assuming that the speed of sound in air is about 340 m/s, in 3 seconds it will travel 340 m/s X 3 seconds = 1020 m. There is no appreciable delay for the flash, so the storm is slightly more than 1 km away.

The energy in ordinary light is greater than the energy in ordinary sound. The speed of sound is a million times less than the speed of light.

Sound energy dissipates to thermal energy while sound travels in air. For waves of higher frequency, the sound energy is transformed into internal energy more rapidly than low frequency waves. Thus low frequency sounds like a fog horn travel farther through air.

An echo is the reflection of sound. The fraction of energy carried by the reflected sound wave can be large with a rigid smooth surface, and small with a soft irregular surface.

When sound undergoes multiple reflections yet still persists after the source has ceased emitting.

Different speeds of sound in a medium.

Downward. When the speed of sound near the ground is reduced, (such as on a cold day when the layer of air nearest ground is colder than the air above) the higher speed of the wavefronts above cause a bending of sound toward the ground. This is sound clearly heard over considerably longer distances.

Changing temperature changes the speed of sound in water. This is problematic for surface vessels that bounce high-frequency waves off the ocean bottom to chart. But its a feature that subs avoiding detection take advantage of!

Sound above the frequency of human hearing. Ultrasound is composed of frequencies higher than human hearing range.

1530 meters: 1 second up, and 1 second down.

The table is forced to vibrate, and its larger surface area vibrates more air than the tuning fork. This is forced vibration.

Elasticity and shape of the object. It will vibrate at its own characteristic frequency. Ex. a wrench and baseball bat make different sounds when hitting the floor. Each has its own natural frequency.

When the frequency of forced vibrations match an object's natural frequency, resonant amplification occurs. It does need a force to pull it back into its starting position, and enough energy to keep it vibrating. Ex. a child's swing

The natural frequency of the electronics is tuned to resonate with the frequency of one station.

The resonant amplification of bridge motion destroyed the bridge. Wind produced an irregular force in resonance with the natural frequency of the bridge, steadily increasing the amplitude of vibration until the bridge collapsed.

When both waves have the same amplitude and when the crest of one wave overlaps the trough of another. Destructive wave interference occurs when two identical waves, out of phase, are superimposed and destroy each other.

All waves (refer to Chapter 19!)

The sound is cancelled when added to its mirror image. Ex. The mirror image wave pattern of the sound signal is combined with the actual sound, and cancels out the noise.

Beats are produced by interference of two waves of slightly different frequencies, heard as a throbbing effect in sound waves.

*4 Hz*

the ear will hear 264 Hz, which will be at *4 Hz* (266 Hz - 262 Hz)

267 Hz will be heard, and some people will hear it throb *10* times each second (272 Hz - 262 Hz). Beat frequencies higher than 10 Hz are normally too rapid to be heard.

A radio wave is an electromagnetic wave that travels at the speed of *light*, whereas a sound wave travels at the speed of *sound* through air or another elastic medium.

yes, the sound wave is a pressure wave (an increase in pressure) followed by a low pressure (reduction in pressure) trough, relative to normal air pressure. After the sound wave passes, the air it passed through returns to its original pressure.

not as many waves would reach you, and you couldn't hear the concert!

Earthquakes emit both pressure and shear waves (known as P and S waves); P waves travel faster through the Earth than S waves. When P and S waves reach a seismic station, they leave characteristic traces on the seismograph, so it is easy for an experienced user to determine the time of arrival of the first P wave and of the first S wave. Calibrate how far away the earthquake was given the P-S arrival time difference.

Space is a vacuum so the explosion has no sound and light travels faster than sound so we would see the explosion long before we heard it.

Sounds of lower frequencies travel farther through air than sounds of higher frequencies. Also, solids conduct sound better than air. The natural frequency of large walls, floors, and ceilings is lower than the natural frequency of smaller surfaces; bass notes more easily set them into forced vibrations and resonance.

If sound waves have the same frequency, they can be totally in phase, totally out of phase, or anything in between, but their waves always either reinforce or cancel each other, so that the "summed sound" is either louder or softer than the individual sounds. But if the two sound waves are of different frequencies, they cancel each other except when their crests coincide; this amplification produces the "beat" phenomenon.