Foundations of PhysicsSound Notes

The Nature of Sound Sound travels in longitudinal waves consisting of oscillating

compressions and rarefactions through the air.

Sound travels at 340 m/s in air at 20 C

Compressions

Rarefactions

The Nature of SoundFor each increase of 1°C above 0°C, speed of sound increases by 0.6 m/s.

The speed of sound also increases as the density of the medium increases.

in air = 340 m/s)in warm air > 340 m/sin water = 4 times faster than airin steel = 15 times faster than air

Frequency and Pitch

• Pitch - The highness or lowness of the sound

• Depends on the frequency of the sound wave

Amplitude and Loudness Loudness – describes the intensity of the sound.

Loudness is measured in decibels (dB)

Depends on the amplitude of the sound wave (energy of the sound wave)

The Doppler EffectThe shifting of the frequency (pitch) of a

sound wave due to the motion of the source of the sound or the observer of the sound (or both).

Stationary Source

Sound waves radiate out equally in all directions

Moving Source

Sound waves are pushed together in the direction of motion and spread farther apart as the source moves away

Higher frequency waves

Lower frequency waves

ResonanceResonance occurs whenever successive oscillations are applied to a vibrating object in rhythm with its natural frequency.

AcousticsThe study of sound wave production and

behaviorIncludes other fields including music ,

architecture, engineering, medicine, oceanography, and zoology.

Human HearingResearch the internet to determine what

frequencies humans can hear. Compare these frequencies to at least two other animals.

Research the internet to determine the loudness scale of human hearing. Explain how loud sounds can actually damage your hearing and cause physical pain.

Human HearingHumans can hear frequencies from 20 Hz to

20,000 Hz.Sounds louder than 130 dB can cause

physical pain because the ear receives so much energy the ear drum and ossicles vibrate too much and can be permanently damaged.

Human Hearing

Loudness scale

Music and Musical InstrumentsUse the following link to discover how the

four classes of musical instruments produce different notes.

http://method-behind-the-music.com/mechanics/

Music and Musical InstrumentsBrass and woodwind instruments change the

pitch of the notes by changing the length of the vibrating air column inside the instrument.

The longer the vibrating air column, the longer the wavelength of sound produced. Longer wavelength sounds have lower frequencies resulting in a lower pitch sound.

Music and Musical InstrumentsString instruments change the pitch of the

notes by changing the length of the vibrating string. Longer vibrating strings produce sounds with longer wavelengths.

As the wavelength of the sound increases, the frequency and pitch decreases.

Acoustic instruments have hollow bodies to help amplify the sound produced by the vibrating strings.

Music and Musical InstrumentsPercussion Instruments produce different

pitch notes by causing different lengths of materials to vibrate.

Longer vibrating objects result in longer wavelength sound waves and lower frequencies and pitches.

Many percussion instruments have hollow spaces to help amplify the sound produced by the vibrating object.