Sound

Sound Waves

• Sound is a disturbance that travels through a medium as a longitudinal wave.

Sound Waves

• A sound wave begins with a vibration.– These vibrations disturb nearby air particles,

which move in compressions and rarefactions away from the source.

Sound Waves

• Sound normally uses air as its medium, but it can move through solids and liquids, also.– For example, when you knock on a door, the wave

moves through the particles in the door.

Sound Interactions

• Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with each other.

Sound Reflection

• A reflected sound wave is called an echo.

Diffraction

• Sound waves do not always travel in a straight line.

• Sound can bend around a corner or through an opening, which is why you can hear someone talking around the corner from you.

Sound Speed

• At room temperature, sound travels at about 343 m/s.– That means that in only one second, sound can be

hear 343 meters away.

Sound Speed

• Sound can travel at different speeds if it is in different mediums or at different temperatures.

Sound Speed

• The more elastic a medium is, the faster sound will travel through it.– Elasticity is the ability of a material to bounce back

after being disturbed.

Sound Speed

• The denser a medium is, the slower a sound wave will move.– This is because the material does not move as

quickly as less dense materials.

Sound Speed

• Sound travels faster at warmer temperatures.– The warmer a temperature is, the more energy its

particles have, so the faster the particles can move.

Loudness

• Loudness describes your perception of the energy of sound.

• Loudness depends on two factors:– The amount of energy used to make the sound.– The distance from the sound.

Loudness

• Energy– In general, the greater the energy used to make a

sound, the louder the sound will be.– More energy creates a larger amplitude. The

higher the amplitude, the louder it sounds.

Loudness

• Distance– Loudness increases the closer to the source of the

sound you are.– This occurs because as the sound wave gets

further from the source, it needs to cover a larger area, so it is more spread out.

Loudness

• The loudness of a sound is measured in decibels (dB).– A sound you can barely hear is 0 dB.– Each 10dB increase represents a tenfold increase

in the intensity of the sound.

Pitch

• The pitch of a sound is a description of how high or low the sound seems.

• The pitch of a sound that you hear depends on the frequency of the sound wave.

Pitch

• Sound waves with a higher frequency have a high pitch.

• Most people hear sounds with frequencies between 20Hz and 20,000 Hz.

Pitch

• Sound waves with frequencies above the normal human range of hearing are called ultrasound.

• Sound waves with frequencies below the normal human range of hearing are called infrasound.

Pitch

• As we observed in our lab, pitch can change due to the tightness or size of the object creating the sound.

The Doppler Effect

• The Doppler Effect is a change in frequency due to a moving sound source.

The Doppler Effect

• As a sound source moves towards you, its frequency is going to be higher than at a resting position.

The Doppler Effect

• As a sound source moves away from you, it will have a lower frequency than it does at rest.

Shock Waves

• If an object is moving fast enough, it can break the sound barrier.

• This means it is moving faster than the speed of sound, so it is in front of the sound waves it is creating.

• This is known as a shockwave.– Supersonic jets create shock waves.

Shock Waves

• As a shock wave passes, you hear a sonic boom.

Echolocation

• Echolocation is the ability to use reflected sound waves to determine distance or locate objects.

• Some animals, including bats and dolphins, use echolocation to navigate and find food.

Ultrasound

• *Remember that ultrasound is sound with a frequency to high for humans to hear.

• Ultrasound technologies are used to observe things that cannot be seen directly.

Ultrasound

• Two common ultrasound technologies are:– Sonar– Ultrasound Imaging