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Learning Introductory Physics with Activities

Section 17.4 Traveling Waves

Subsubsection Activities

Activity 17.4.1. Generating a Wave.

A string is tied to a mass on a spring. The mass oscillates 5 times each second, getting as far as \(8.0 \mathrm{~cm}\) from equilibrium, generating a wave on the string whose crests are separated by \(7.2 \mathrm{~m}\text{.}\) Find the following:
  1. Wavelength
  2. Amplitude
  3. Period
  4. Frequency
  5. Wave speed
  6. Initial phase
  7. An equation for the displacement of the string as a function of \(x\) and \(t\)

Activity 17.4.2. Three Waves.

You create three waves on three identical strings that have the same period \(T\text{,}\) but they start at a maximum displacement at different times: \(y_{\text{max}}\) occurs at \(t=0\) for wave 1, at \(t=T/6\) for wave 2, and at \(t=5T/6\) for wave 3.
(a)
Sketch a history graph of each wave (displacement vs. time).
(b)
Sketch a snapshot graph of each wave at \(t=T/6\) (displacement vs. position).
(c)
Write an equation for each wave.

Activity 17.4.3. Leaf on a Lake.

You are watching a leaf bobbing up and down on the surface of a lake (both above and below the surface of the water). You measure the leaf’s highest point above the surface of the water to be \(12 \mathrm{~cm}\text{.}\) After \(3 \mathrm{~s}\text{,}\) the leaf returns to its highest point above the surface of the water.
(a)
Write an equation for the position of the leaf as a function of time.
(b)
What is the leaf’s highest speed during its motion?
(c)
Find all the instants in time when the leaf has this speed.
(d)
How do you think you could use your equation for the position of the leaf to write an equation for the vertical displacement of the water a distance \(x\) away from the leaf? Try writing such an equation!
(e)
Start the following simulation.
  1. Explore each of the three tabs. Make a list of your observations as you go.
  2. In the water tab, what do you think would happen if you placed a leaf on the surface of the water near the right edge of the tank? Draw a displacement vs. time graph (like those provided in the simulation) for the leaf.
  3. How does each experiment change if you change the frequency? Explain briefly.
  4. How does each experiment change if you change the amplitude? Explain briefly. (You may want to turn your sound on.)