What is a sound wave?

What is a sound wave?• Mechanical wave – longitudinal

*A vibration

*Particles of medium are disturbed

*Causes a wave

causes

Most common medium is air Can travel through solids and liquids

Sound Interactions• Reflection– Echo - when a sound wave reflects off a surface.• Harder and smoother the surface the stronger the reflection.

• Diffraction– Through openings (doorways)– Around corners

• Interference– Can be:• Destructive – sound will be fainter• Constructive – sound will be louder

Speed of Sound (SOS)

• 343 m/s – at room temperature through air• Depends on medium sound is traveling

through–3 characteristics of the medium affect SOS:

1. Elasticity2. Density3. Temperature

Elasticity• The ability of a medium to bounce back

after being disturbed.• More elastic medium – the particles

bounce back faster – sound travels faster.• Less elastic medium – the particles bounce

back slowly – sound travels slower.• From faster to slower: solids > liquids >

gases

Density• Sound travels more slowly in

denser mediums• Due to particles not moving as

quickly back to rest position in denser materials (too crowded).

Temperature• Sound travels more slowly

at lower temperatures than higher temperatures.•Because particles move

slower in lower temperatures.

SOS final thoughts• The faster the particles of the medium can

return to rest position – the faster sound will move through medium.– More elastic – faster (bounce back quicker)– Less dense – faster (not as crowded)– Higher temp – faster (particles naturally move faster)

• First person to break sound barrier (go faster than sound) – Chuck Yeager– Flew at higher altitude b/c lower temp = lower SOS

Properties of sound• Loudness – depends on

amount of energy used to create sound (amplitude of wave).• Pitch – depends on frequency

of wave.

Loudness• Depends on 2 things:–The amount of energy it takes to make the

sound.–The distance from the source of the sound.

• Decibel (dB) – unit for loudness of sound• Intensity – The amount of energy a sound

wave carries over a certain amount time in a particular area.

Pitch• How high or low the sound seems• High pitch – high frequency• Low pitch – low frequency• Ultrasound – sound waves with freq. above

normal human hearing. (Usually above 20,000 Hz)

• Infrasound – Below human range of hearing (usually under 20 Hz)

The Doppler Effect• The change in frequency (pitch) as a source

of sound MOVES in relation to the observer.–Pitch increases as source moves toward

observer.–Pitch decreases as source moves away.

• Think of a siren approaching then passing by. It sounds different.

• Can happen with light waves also.