Waves on a String Lab

Directions: Go to the website: http://phet.colorado.edu/en/simulations/category/physics

1. Open Waves on a String, investigate wave behavior using the simulation for a few minutes.  As you look at the waves’ behavior, talk about some reasons the waves might act the way they do.

2. Write a list of characteristics that you will use in this activity to describe the waves. Describe each characteristic in words that any person could understand. Leave some writing space for characteristics that you might think of later during the activity.

Equilibrium: Resting/balanced position of the string
Amplitude:the maximum distance that one point of the string gets away from the equilibrium (up and down)
Oscillation: Vibration around an equilibrium
Crest: highest point of the wave
Trough: lowest point of the wave
Wavelength: The distance from crest to crest (see above)
Frequency:The number of cycles the wave completes in a certain amount of time
Medium: the matter that the wave travels through
Wavespeed: The velocity of the wave on the medium
Pulse: a single disturbance
Periodic: acontinuous periodic disturbance

Tension: pulling force exerted by a string on another object.

Damping: restraining of vibratory motion (shock absorbers and carpet pads)

3. With the Oscillate button on and with No End checked, investigate waves more carefully using the Amplitude slider. Write answers to the following after your group has talked about each and agreed.

a) Define Amplitude in everyday language.

Amplitude: the maximum distance (height) that the string gets away from the equilibrium (the dotted line on the simulation.

b) Explain how the wave behaves as the Amplitude changes using the characteristics you described in #2

At zero amplitude, the string is at equilibrium, or basically flat. As the amplitude increases, the crest gets higher and the trough gets lower. The crest and trough will always be the same distance from equilibrium. The wavelength stays the same no matter the amplitude. This wave is also periodic, not a pulse. The wavespeed is also the same no matter what the amplitude may be.

c) If you would like, you can use a slinky on the floor for some investigations and explain how you could change the Amplitude of a wave.

Using a slinky, you can change the amplitude by just pushing the end of the slinky farther away or less farther away than just 15 inches. This will give you a larger or smaller amplitude for your slinky wave. 

4. Repeat step number 3, for Frequency, Tension and Damping.

a) Define Frequency in everyday language.

The number of cycles that the wave completes in a certain amount of time.  For this simulation, it is the speed of the pump.

b) Explain how the wave behaves as the Frequency changes using the characteristics you described in #2

When you increase the frequency, the amplitude is no affected. The wavelength also gets smaller when the frequency is increased.

c) If you would like, you can use a slinky on the floor for some investigations and explain how you could change the Frequency of a wave.

Using a slinky, you can increase the frequency by varying the speed at which you create the wave.

a) Define Tension in everyday language.

Pulling force exerted by a string on another object.

 b) Explain how the wave behaves as the Tension changes using the characteristics you described in #2

When you have high tension, the balls on the string are all attached.  However, even when you lower the tension just a little bit, the balls are no longer touching and the amplitude becomes very hard to determine.  With low tension, the wavelength doesn't change.

c) If you would like, you can use a slinky on the floor for some investigations and explain how you could change the Tension of a wave.

I don't think you can change the tension of a slinky because it is a solid figure where you can't change the tension of the metal. 

a) Define Damping in everyday language.

The restraining of vibratory motion (like shock absorbers and carpet pads)

 b) Explain how the wave behaves as the Damping changes using the characteristics you described in #2

With no damping, the wave will never end. The amplitude and wavespeed will always stay the same. But when you increase the damping, the wave dies quickly. At full damping, the wave only completes one cycle.

c) If you would like, you can use a slinky on the floor for some investigations and explain how you could change the Damping of a wave.

You cannot change the damping of a slinky because the damping of a slinky is constant. If there was no damping, the slinky would make waves forever.

5. Set Amplitude on high, Frequency, Damping and Tension on low. Also, have on Oscillate, Timer and No End. Use the Pause button to freeze the wave.

a) Place a blank piece of paper on your monitor and trace the wave and the wave generator. Mark the green balls. This is a vertical position- horizontal position graph, label your axes.

b) Quickly press Play, and then Pause again. Use the same piece of paper, put it on the monitor and make sure to get the generator in the same spot. Trace the new wave.

c) Write about the differences and similarities in the characteristics. You may have to do some more tests by pressing Play, then Pause and tracing to test your ideas.

The main difference is that for the first graph, the line started in the middle, where in the second it started at the crest of the wave generator.  The graphs are pretty similar besides the fact that the dots are in different spots. They are very similar, and both of the graphs both get smaller towards the end together.

d) Try some other settings and talk about why I recommended the settings that I did.

 With a lower amplitude, it would've been harder to trace the graph.With a higher frequency, you almost can't tell the pattern of the graph.

6. Set Amplitude on high, Frequency, Damping and Tension on low. Also, have on Oscillate, Timer and No End. Use the Pause button to freeze the wave.  

a) Measure the vertical location of a green ball with a ruler.

B) Record the vertical position and time.

b) Quickly press Play, then Pause repeatedly to make a data table the vertical position of the green ball versus time.

c) Make a graph of vertical position versus time.

d) Write about the differences and similarities between vertical position- horizontal position graphs and vertical position-time graphs.
The difference is that the vertical position-time graph looks much more structured than the first one.  Yo u can more easily see the pattern of the vertical position-time graph. The similarities are that on both graphs, the lines are going down and up, all while moving to the east.

7. Investigate how waves behave when the string end is Fixed and Loose with Manual settings. Discuss the behavior with your partners. Test your ideas and the write a summary.

I feel like when the string end is fixed, the damping is a little harsh and the wave doesn't come to a natural end. If it weren't fixed, the last green ball would move up and down a bit. When the string is loose, the wave ends more naturally. When the frequency is 100, it doesn't change the fixed end but the loose end moves much more quickly. With the loose end, a higher amplitude means a higher amplitude on the ending pole too.

Post to your blog the results of this investigation. You must include all sections that involve the verbs WRITE, RECORD and MAKE.