INTRODUCTION TO SOUND

Sound Waves, Pitch, and Loudness

How Does Sound Travel? Sound waves are produced by vibrations. Sound travels as longitudinal waves. Sound waves travel in all directions.

Sound Waves, Medium, and Speed

Sound requires a medium. Sound cannot travel in a

vacuum. When there is no air, there

is no sound. The speed of sound…

Changes when the medium changes. Sound usually travels faster

in denser media. Depends on temperature.

Sound travels faster in warmer temperatures.

Sound Waves, Pitch, and Frequency

The pitch of a sound depends on the frequency of the sound wave.

High Frequency = High Pitch Low Frequency = Low Pitch

What Frequencies Can We Hear?

Humans can hear frequencies between 20 Hz - 20,000 Hz.

Below 20 Hz – infrasonic Above 20,000 Hz – ultrasonic

Younger people can generally hear higher frequencies; as you age, you lose the ability to hear high-pitched sounds.

Doppler Effect The Doppler effect occurs

when the source of the sound is moving relative to the listener.

Example: Police Siren As the police car moves

toward you, the siren has a higher pitch.

As the police car moves away from you, the siren has a lower pitch.

Example Video

Sound Waves, Amplitude, and Loudness

The amplitude of a sound wave determines its loudness (or volume).

High Amplitude = More Energy = Loud Sound

Small Amplitude = Less Energy = Quiet Sound

Measuring Loudness The loudness of a

sound is measured in units called decibels (dB).

For every 10 dB, the intensity of the noise gets 10X louder.

Continued exposure to noise at 85 dB and higher cause hearing loss.

Quick Check

Of the three graphs below, which sound has the highest pitch? Which

is the loudest? Why?

Warm-UpWhich sound wave has the highest

pitch?Which is the loudest?