Aka Another Way to Show Your Support for the Cubs While at Wrigley Field

Name

Date______

Let’s do the Wave!

(aka Another way to show your support for the Cubs while at Wrigley Field)

Directions: Use the simulation “Waves on a String” (in the Sound & Waves) section on the website http://phet.colorado.edu to complete this activity. Click “Run Now” once you found it.

Part I: Wave Terminology and Relationships

1.  Define the following with respect to a wave:

a)  Wavelength

b)  Period

c)  Frequency

d)  Amplitude

e)  Crest

f)  Trough

2.  Select “Oscillate” and “No end”. Create a wave with an amplitude of 0.75 cm and frequency of 1.0 Hz. Damping should be 0 and Tension should be high. Check the box labeled “Rulers”. After waves begin propagating, click the Pause button. Move the rulers as needed. What is the wavelength of this wave, in cm? What is the amplitude of this wave, in cm?

3.  Change the Frequency setting to 2.0 Hz and measure the new wavelength and amplitude of the wave. Compare these values to those measured in #2. Are they greater, equal or less? By what approximate ratios?

4.  Change the Frequency setting to 3.0 Hz and measure the new wavelength and amplitude of the wave. Compare these values to those measured in #2. Are they greater, equal, or less? By what approximate ratios?

5.  Make a statement about the relationship between wavelength and frequency. Are they directly or inversely related?

6.  Make a statement about the relationship between amplitude and frequency as well as amplitude and wavelength. Are they related? If so, how?

7.  Make a statement about the relationship between period and frequency. Are they directly or inversely related?

Part II: Other Factors Affecting Waves

8.  Select “Oscillate” and “No end”. Create a wave with an amplitude 0.75 and frequency of 2.0 Hz. Gradually change the Damping setting from 0 - 100 and describe what happens to the wave.

9.  Think About It: What is damping? Why does it occur? Where does the energy the wave loses go?

10.  Change the Damping setting back to 0. Select the “Fixed End” option. Also select the “Pulse” option. Click the yellow Reset button followed by the green Pulse button. Describe what happens to the wave. Does it travel back with the same orientation (i.e. as a crest) as when it traveled forward?

11.  Select the Loose End option and describe what happens to the wave. Does it travel back with the same orientation as when it traveled forward?

12.  Lower the tension about halfway in the string. Describe what happens to the wave. What factors does it change (amplitude, wavelength, period, frequency, speed)?

13.  Return the tension to high. Each individual particle (red or green ball) begins at its equilibrium position with zero displacement. Describe how each particle’s initial displacement before the wave pulse passes through compares to its final displacement after the wave pulse passes through.

14.  a) Click on the Loose End. Click on the green pulse button. When the pulse is about half way down the chain, click on the green pulse button a second time. Observe the two pulses through several cycles. It may be easier to click pause/play and watch the wave move one step at a time. When two crests or two troughs meet, what happens to the wave at the moment they overlap? What is this called?

b) When a crest and trough meet, what happens to the wave at the moment they overlap? What is this called? It

may be easier to click pause/play and watch the wave move one step at a time.

Conclusion Questions and Calculations:

1.  When a wave strikes a boundary that is more dense than the original wave medium (essentially a fixed end), the wave comes back upright / inverted.

2.  When a wave strikes a boundary that is less dense than the original wave medium (essentially a free or loose end), the wave comes back upright / inverted.

3.  Two wave pulses strike each other traveling in opposite directions. If the first pulse has amplitude of +18cm and the second pulse +24 cm, what is the amplitude of the resulting interfered wave? ______cm.

4.  After the two wave pulses pass each other, the original waves are enlarged / reduced / unchanged.

5.  A wave with peaks separated by .34 m has a wavelength of ______m.

6.  Imagine standing near the door of a dog house. If a puppy comes running out every three seconds, what would the period of the exiting puppies be? ______s.

7.  Considering the above, how many puppies (or fraction of a puppy) exit every second? ______s-1.

8.  If a certain wave has a new wave crest created every 2.5 seconds, the period is ______s.

9.  What is the frequency of the wave described above in #8? ______s-1.

10.  Using the above formula for wave speed, how fast does a sound wave move that has a frequency of 410 s-1 (Hz) and a wavelength of 83 cm? ______m/s.