Chapter 15.1 Notes

Chapter 15: Sound

Sound, is a longitudinal mechanical wave produced as one molecule bumps into another molecule. The velocity of a sound wave depends on the temperature of the air; the speed in air is 331.5 m/s at 0º C. This speed increases with temperature about 0.6 m/s)/Cº .

The speed of sound is directly proportion to the elasticity of the vibrating medium, and it is inversely proportion to the inertia of the medium. In general, denser media tend to support faster sound velocities. Some examples you should be familiar with

Doppler Shift

The perceived frequency due to doppler shift can be calculated as follows:


Practice: solve problems 11 and 12 in the chapter review problems, and problems 9 and 10 in the supplementary set on page 699 of the text.

Here are a couple of links where you do an interactive internet activity with the Doppler effect:

Pitch and Loudness

Frequency and intensity are physical characteristics of sound.




Resonance occurs when a vibration is reinforced at the natural frequency of some object, and the frequency is amplified. A sound vibration passing through a tube may cause air in the tube to vibrate at the same frequency as the sound wave, and thus the sound becomes louder. This only happens if the tube itself is of a particular length relative to the wavelength of the sound:

homework: set #1 ch 15 probs 1-6. set #2 problems 24-33. set #3 problems 7-12, 34-38

video: The Tacoma Narrows Bridge

lab: experimentally determine the frequency of tuning forks using resonance.