Physics 101: Lecture 32 Waves and Sound. Today’s lecture will cover Textbook Sections 16.1 - 16.5 Review: Simple Harmonic Motion (Chapter 10).
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x = A cos (wt)
i.e. the object periodically moves back and forth between
the amplitudes x=+A and x=–A.
The time it takes for the object to make one full cycle is
the period T=2p/w=1/f, where f is the frequency of the
Thus, the angular speed in terms of T and f reads
w = 2p/T and w = 2 p f
direction of travel of the wave.
travel of the wave.
The source of the wave, i.e. the disturbance, moves continuously in
simple harmonic motion, generating an entire wave, where each
part of the wave also performs a simple harmonic motion.
Types of Waves
v = / T
not on the amplitude, wavelength or period:
and T are related !
Is the speed of a wave particle the same as the speed of the wave ?
No. Wave particle performs simple harmonic motion: v=A w sin wt.
Suppose a periodic wave moves through some medium. If the period of the wave is increased, what happens to the wavelength of the wave assuming the speed of the wave remains the same?
1. The wavelength increases
2. The wavelength remains the same
3. The wavelength decreases
The speed of sound in air is a bit over 300 m/s, and the speed of light in air is about 300,000,000 m/s. Suppose we make a sound wave and a light wave that both have a wavelength of 3 meters. What is the ratio of the frequency of the light wave to that of the sound wave?
1. About 1,000,000.
2. About 1,000.
3. About 0.000001.
f = v/
fL/fS = vL/vS = 1,000,000
T=Tension : the greater the tension in the string the greater
the pulling force the particles exert on each other
and the faster the wave travels.
m=mass/length of the string = m/L= linear density of the spring:
the smaller the mass the greater the acceleration for
the same pulling force and the faster the wave travels.
A rope of mass M and length L hangs from the ceiling with nothing attached to the bottom (see picture). Suppose you start a transverse wave at the bottom end of the rope by jigglingit a bit. As this wave travels up the rope its speed will:
3. Stay the same
the tension gets greater as you goup