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General Physics
Wave Unit – Big Springs Activity
Purpose: To explore the properties of mechanical waves.
Materials:
-
Clip board, green sheet
Long, Flexible Tape Measure
-
Stopwatch & Masking tape
Super Slinky
Instructions:
1. Record data & observations in your lab journals and responses on a separate sheet
2. First, a few ground rules (for the safety of you and the equipment!):
a. Slinkies do NOT work on the stairs. Do not attempt to make them walk down the stairs.
They are too long and the stairs are too short—sorry. As neat as it would be, it won’t
work and the Slinky will more than likely tangle. Please don’t even try it!
b. Slinkies are to be used on the floor ONLY. Please do not wiggle them in the air.
c. Please do not spiral or twirl the Slinky. For that matter, please do not do anything that
has the potential of entangling the coils or over-stretching the Slinky at all.
d. Please hold the base of the Slinky stand firmly with one hand and the top firmly with
the other so the Slinky does not fall off the stand as you move to your lab area.
Predictions:
Please complete the following predictions BEFORE starting the activity. Select one choice from the
options listed AND explain why you chose that response.
1. A wave pulse is created by very sharply moving the free-end of a cord (or spring) to the side
and back to its original position. How will the speed of this wave pulse be affected if you
increase the tension on the cord (tighten it)?
A. The speed will NOT be affected by the tension of the cord.
B. The wave pulse will travel SLOWER in the tightened cord.
C. The wave pulse will travel FASTER in the tightened cord
2. A continuous wave is created by moving the end of a cord back and forth at a steady rate. If
the distance the cord is displaced doubles (i.e. you move your hand back and forth twice as
far) but the rate at which you create the wave remains constant, how will the speed of the
wave be affected?
A. The speed will NOT be affected by the amplitude of the cord.
B. The wave pulse will travel HALF AS FAST when the amplitude is doubled.
C. The wave pulse will travel TWICE AS FAST when the amplitude is doubled.
D. The wave pulse will travel FASTER, but not necessarily twice as fast when the
amplitude is doubled.
E. The wave pulse will travel SLOWER, but not necessarily half as fast when the amplitude
is doubled.
Over
Predictions continued:
3. What do you think will happen when two wave pulses that are created at opposite ends of
the Slinky but with the same amplitude meet? Explain your prediction.
4. A wave pulse generated by moving one end of the Slinky to the side and back to the original
position travels at a certain speed.
a. How do you think the speed of the wave pulse will be affected if you keep the
amplitude constant, but generate the wave pulse at a FASTER rate? Explain your
prediction.
b. How do you think the speed of the wave pulse will be affected if, keeping the
amplitude constant, you generate the wave pulse at a SLOWER rate? Explain your
prediction.
Procedure and Analysis Questions:
And now for some work with the Slinky! Answer questions thoroughly. Measure & mark w/tape
1. Stretch the Slinky approximately 7 m (but no more than 8 m); you should hold one end
and your partner should hold the other.
2. Partner A: Do nothing to the Slinky other than hold your end firm and still.
Partner B: Create a wave pulse by firmly and quickly jerking your hand to your left and
back to its original position ONCE.
Sketch the wave pulse—describe the appearance of the Slinky when the wave pulse was
approximately halfway between you and your partner.
Observations:
Describe the behavior of the Slinky. In what direction were the coils of the Slinky moving?
How do you know? What type of wave is this?
3. Partner A: Hold your end of the Slinky firm and still.
Partner B: Generate the wave pulses as described.
Quantitatively determine how fast the wave pulse travels from one end of the Slinky to the
other when you generate the wave pulse at different frequencies. Report your results in
the tables below and show one calculation for the average speed of the wave pulse below
the tables:
Table 1: Time Measurements for a Wave Pulse to Travel a Measured Distance
Relative Frequency
Distance Measured
(m)
Time to Travel Measured Distance
(sec)
Trial 1
Trial 2
Trial 3
“Normal”
Faster Rate
(higher frequency)
Slower Rate
(lower frequency)
Table 2: Average Times and Calculated Wave Speeds for Each Frequency
Relative Frequency
Average Time
(sec)
Average Wave Speed
(m⁄s)
“Normal”
Faster Rate
(higher frequency)
Slower Rate
(lower frequency)
Please show a sample calculation of wave speed
DID the frequency at which you generated the pulse significantly affect the speed of the
wave pulse? Explain using the data from above.
4. What happens to the amplitude of the wave pulse as it travels? Describe your observations.
Do you observations depend on the original amplitude you generate?
WHY? How can you explain your observations?
5. Quantitatively determine if the amplitude affects the speed of a wave.
Table 3: Time Measurements for a Wave Pulse to Travel a Measured Distance
Relative Amplitude
“Normal”
Larger Amplitude
Smaller Amplitude
Distance Measured
(m)
Time to Travel Measured Distance
(sec)
Trial 1
Trial 2
Trial 3
Table 4: Average Times and Calculated Wave Speeds for Each Frequency
Relative Amplitude
Average Time
(sec)
Average Wave Speed
(m⁄s)
“Normal”
Larger Amplitude
Smaller Amplitude
6. Partner A: Hold your end of the Slinky firm and still.
Partner B: In the same way the pulse was generated for question 5, generate 2 pulses in
quick succession (one right after the other).
Describe what happens to the distance between the two wave pulses as they travel the
length of the Slinky.
If the two pulses are generated at a different rate (i.e. change the distance separating
them), do your observations change?
7. The distance between two pulses is, essentially, what we can measure as the wavelength of
a wave. Determine which of the following factors affect this property of a wave and
explain what you did to support your answer experimentally:
a. Amplitude  YES NO
b. Frequency  YES NO
c. Increased Tension in the spring  YES NO
d. Decreased Tension in the spring  YES NO
8. Partner A: Create a wave pulse by firmly and quickly moving your hand forward towards
your partner and then back to its original position ONCE.
Partner B: Do nothing to the Slinky other than hold your end firm and still.
Sketch the wave pulse—describe the appearance of the Slinky when the wave pulse was
approximately halfway between you and your partner.
Observations:
Describe the behavior of the Slinky. In what direction were the coils of the Slinky moving?
How do you know? What type of wave is this?