Conceptual PhysicsConceptual PhysicsNotes on Chapter 25Notes on Chapter 25

SoundSound

SoundSoundAll sounds are produced by the

vibrations of material objects.

Pitch describes our impressions about frequency or sound when produced by vibrations.

SoundSoundA “normal” person can distinguish

sound frequencies between 20 and 20,000 hertz.

• below 20 hertz is known as below 20 hertz is known as infrasonicinfrasonic..• above 20,000 hertz is known as above 20,000 hertz is known as ultrasonicultrasonic..

NOTE: NOTE: NoNo human can hear above or human can hear above or below 20 - 20000 hertz.below 20 - 20000 hertz.

SoundSound When something vibrates, it causes a

wave that compresses and stretches.

In physics we call this Compression and Rarefaction.

SoundSound Sound needs a medium to travel through. Sound needs a medium to travel through.

But sound travels at different speeds in But sound travels at different speeds in different mediums.different mediums. AirAir --- can range from 330 m/s - 350 m/s --- can range from 330 m/s - 350 m/s

• NOTE: NOTE: For ALL problems we will take the average speed of For ALL problems we will take the average speed of 340 m/s340 m/s

LiquidLiquid - can range from 1325 m/s - 1375 m/s - can range from 1325 m/s - 1375 m/s• NOTE: NOTE: For water we will take the average speed of 1360 m/s For water we will take the average speed of 1360 m/s

(Water)(Water)

SolidSolid - Can range from 4500 m/s - 6000 m/s - Can range from 4500 m/s - 6000 m/s• NOTE: NOTE: For solids we will take the average speed of 5100 m/s For solids we will take the average speed of 5100 m/s

(Steel)(Steel)

SoundSoundLOUDNESS

Loudness is subjective. Each person hears sound different due to each persons brain interrupts sound different.

Loudness is measured in Decibel (dB). Decibels are based on a logarithmic variation.

EX: 40 dB is 100 times as loud as 20 dB 100 dB is 10 times as loud as 90 dB

• See Table 26.1 Pg. 394

SoundSound Forced vibrationForced vibration is when a vibrating is when a vibrating

object causes a object in contact with it object causes a object in contact with it to also vibrate.to also vibrate.

SoundSound

Interference of Interference of sound waves sound waves affects the affects the loudness of loudness of sounds.sounds.

SoundSound Different objectsDifferent objects create create different sounddifferent sound

waves.waves.

SoundSound

Sound waves Sound waves can produce can produce HARMONICSHARMONICS. .

SoundSound

HarmonicsHarmonics can can be easily be easily demonstrated demonstrated with a tuning with a tuning fork and tubefork and tube..

SoundSound

BEATSBEATS BeatsBeats happen happen

when two waves when two waves interfere with each interfere with each other in a way that other in a way that some of the wave some of the wave energy overlaps energy overlaps constructively and constructively and some overlap some overlap destructively. destructively.

SoundSound

If you If you subtractsubtract the frequencies of the frequencies of the two tuning forks, you can get the two tuning forks, you can get the beat frequency.the beat frequency.

• EX:EX: 262 Hz and 266 Hz 262 Hz and 266 Hz

262 Hz and 272 Hz262 Hz and 272 Hz