Understanding Wave Motion Using the Simulation

Pulses

When you click on the link, the webpage opens, and your screen will look like Figure 1. Set the damping control to zero since we ignore dissipative effects. Also set the tension to midway. Select Manual and No End.

Figure 1: Starting screen settings.

Exercise 1: The Speed of a Wave

If you move the cursor to the leftmost or starting green circle, the cursor turns into a little hand. When you move the hand up and down you generate a pulse. If you jiggle the end up and down continuously, you generate a wave. Practice until you can generate a single pulse like Figure 2.

Figure 2: A single pulse.

Generate pulses with both large and small vertical displacements (amplitude) and carefully observe the results. Choose the correct observation from the box below.

A. The larger the vertical displacement, the faster the pulse travelled.

B. The larger the vertical displacement, the slower the pulse travelled.

C. The vertical displacement did not affect the speed of the pulse.

Next move your hand up and down fast or slowly so that you can generate narrow or broad pulses and carefully observe the results. Choose the correct observation from the box below.

A. The narrower the pulse, the faster the pulse travelled.

B. The wider the pulse, the slower the pulse travelled.

C. The width of the pulse did not affect the speed of the pulse.

Next generate a pulse and alter the tension in the string and carefully observe the results. Choose the correct observation from the box below.

A. The higher the tension, the faster the pulse travelled.

B. The higher the tension, the slower the pulse travelled.

C. The tension did not affect the speed of the pulse.

Exercise 2: Reflection and Orientation (Phase)

Instead of No End, choose a Fixed End and generate a pulse. Carefully observe the pulse as it reflects off the Fixed End comes back and reflects again off the starting end. Repeat with the right end being a Free End. Choose the correct observations from the box below.

A. The orientation (phase) of a pulse flips upon reflection from a fixed end.

B. The orientation (phase) of a pulse does not change upon reflection from a fixed end.

C. The orientation (phase) of a pulse flips upon reflection from a free end.

D. The orientation (phase) of a pulse does not change upon reflection from a free end.

When the pulse returns and reflects off the leftmost starting end, which is the correct observation from the box below?

A. The left-hand side acts as a fixed end.

B. The left-hand side acts as a free end.

Exercise 3: Superposition

Now choose a Free End and set the tension midway. Next generate two similar pulses so that the pulses are at least halfway apart – see Figure 3. The leading pulse will reflect and move toward the second pulse. Carefully observe the pulses as they superpose each time they pass each other. Choose the correct observation from the box below.

A. When the orientation of the pulses is the same, the amplitudes add.

B. When the orientation of the pulses is the same, the amplitudes partially or totally cancel.

C. When the orientation of the pulse is the opposite, the amplitudes partially or totally cancel.

D. When the orientation of the pulse is the opposite, the amplitudes add.

Figure 3: Superposition of pulses.

Continuous Waves

Next return to No End but choose Oscillate. This will generate a continuous travelling sine wave as shown in Figure 3. Note that you can now control the amplitude of the vertical displacement and the frequency.

Figure 4: Travelling Sine Wave

Exercise 4: Speed of a Wave

Adjust only the amplitude and carefully observe the effects. Choose the correct observations from the box below.

A. The larger the amplitude, the faster the wave travelled.

B. The larger the amplitude, the slower the wave travelled.

C. The amplitude did not affect the speed of the wave.

D. The larger the amplitude, the larger the wavelength of the wave.

E. The larger the amplitude, the smaller the wavelength of the wave.

F. The amplitude did not affect the wavelength of the wave.

Adjust only the frequency and carefully observe the effects. Choose the correct observations from the box below.

A. The larger the frequency, the faster the wave travelled.

B. The larger the frequency, the slower the wave travelled.

C. The frequency did not affect the speed of the wave.

D. The larger the frequency, the larger the wavelength of the wave.

E. The larger the frequency, the smaller the wavelength of the wave.

F. The frequency did not affect the wavelength of the wave.

Adjust only the tension and carefully observe the effects. Choose the correct observations from the box below.

A. The larger the tension, the faster the wave travelled.

B. The larger the tension, the slower the wave travelled.

C. The tension did not affect the speed of the wave.

D. The larger the tension, the larger the wavelength of the wave.

E. The larger the tension, the smaller the wavelength of the wave.

F. The tension did not affect the wavelength of the wave.