Sound

Preview Sound as a Wave A Tree Falls in the Woods Speed of Sound Properties of Sound The Doppler Effect ‘Beats’

Sound as a Wave

Sound as a Wave Sound is a mechanical wave. Travels through a medium as a longitudinal wave.

A Tree Falls in the Woods

A Tree Falls in the Woods When a tree crashes down, the energy with which it strikes the forest floor is transmitted through the ground and the surrounding air. This energy causes the ground and the air to vibrate. If sound is a disturbance that travels through the ground or air, then sound is created even if no one is around.

The Speed of Sound

The Speed of Sound Depends on: Elasticity Density Temperature

Elasticity The ability of a material to retain its shape Rubber bands – high elasticity Clay – low elasticity More elastic = faster sound Solids are more elastic than liquids and liquids are more elastic than gases… therefore sound travels fastest in solids.

Density Density = Mass/Volume Lower density = Faster sound Mass – A measure of how much matter is in an object Volume – The amount of space that matter occupies Lower density = Faster sound Less massive particles take less energy to vibrate

Temperature The measure of the average kinetic energy of the particles in a substance. Kinetic Energy – energy that an object has because of its motion Higher temp. = Faster sound Molecules already vibrating some due to kinetic energy

Properties of Sound

Properties of Sound Intensity, volume, frequency, pitch, and resonance are all properties of sound.

Intensity Increased Amplitude (A) The amount of energy per second carried through a unit area by a wave. Measured in watts per square meter or W/m2

Volume Perception of the intensity of a sound. Measured by decibels or dB. A sound wave of greater intensity generally sounds louder. Music keeps getting louder over the years ‘Something’ by The Beatles, remastered four times

Frequency (f) The number of cycles that pass a given point per second. Measured by Hertz or Hz. People can hear 20 Hz - 20,000 Hz. Ultrasound –above 20,000 Hz. Infrasound –below 20 Hz.

Pitch Perception of the frequency of sound. Sound waves of high frequency have a high pitch, while sound waves of low frequency have a low pitch.

Resonance The increase in the amplitude (A) of vibration that occurs when external vibrations match the object’s natural frequency Tacoma Bridge Microphone/Guitar Feedback

The Doppler Effect

Doppler Effect The apparent change in frequency (f) as the source moves in relation to the listener. As source moves toward the listener, the waves reach the listener with a higher frequency (f) Higher pitch

Doppler Effect Cause – a sound moving towards and away from a listener Effect – the change in pitch and frequency of the sound.

‘Beats’

‘Beats’ Special kind of wave interference Alternates between destructive and constructive

Review Sound as a Wave A Tree Falls in the Woods Speed of Sound Properties of Sound The Doppler Effect ‘Beats’