In the previous chapter we had said amplitude was how much energy a wave had. With sound this equates to how loud the sound appears. The more energy there is the louder it sounds. Larger amplitude= louder sound In order to create more energy in a sound wave, more energy must be given up by the object making the sound

In sound waves energy is referred to as intensity. The more energy there is the greater the intensity of the wave. Intensity decrease the further away you get from the source. Intensity is interpreted by the brain as loudness. More energy = more intensity= louder sound We measure intensity using the unit decibel (dB)

The Decibel Scale

Frequency and Pitch Just as amplitude of a wave relates to its loudness, the frequency of a wave relates to it’s pitch, or how high or low a sound appears to be. Higher pitch =Higher Frequency What was the unit for frequency?

Wavelength doesn’t necessarily correspond to pitch. Slower moving waves will have less frequency even if the compression parts of the wave are closer together Frequency = Pitch (tuba vs. piccolo) Amplitude = Loudness (whisper vs. yelling)

Normal human hearing usually falls between 20 Hz and 20,000 Hz. Sounds above 20,000 Hz are referred to as ultrasonic. This occurs in objects that are vibrating really fast Examples would include things like dog whistles, and bats using echolocation. Humans also use these for medical purposes and for sonar

For sounds that fall below the 20 Hz range we call them infrasonic or subsonic. These are produced by things that vibrate really slow such as wind or machinery. We can’t really hear them but we can feel them. Elephants use this type of wave to communicate with each other. Tones

SONAR Sound Navigation and Ranging In addition to locating prey, bats and dolphins use sound waves for navigational purposes. Submarines do this too. The principle is to send out sound waves and listen for echoes. The longer it takes for an echo to return the further away the object is. This technology is used in commercial fishing to find schools of fish, scientists use it to map the ocean floor, and even special glasses have been made to help the blind navigate. If radio waves are used instead of sound waves we call it radar not sonar

Doppler Effect We have all experienced the Doppler effect at some point. When we stand next to a road and a car approaches, it sounds high pitched. As the car pass it suddenly changes from high to low. The Doppler effect is the change in frequency or pitch of a sound as the source moves.

Doppler Effect Video

If you are moving and not the object you still experience the Doppler effect, because the position relative to the observer is still changing. The Doppler effect occurs in other waves besides just sound. It can occur in light (The red shift of the stars), and in radar. We use the Doppler effect in radar to predict the weather, as well as determine the speed of cars.

Content Check How is intensity and loudness related? How is frequency and pitch related? What is the difference between intensity and pitch? What is the Doppler effect? What is the threshold of pain and permanent damage on the decibel scale? What is an example of an object that has that decibel?