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Making Waves

Published in Resources & Tips and Lesson Plans. Tags: , , , , , , , , , , , , , , , , .

Materials

Materials are per group:

  • Slinky springs
  • Pieces of brightly colored yarn
  • Meter sticks
  • Stop watches
  • Spiral spring
  • Masking tape


Procedure

  • Several different relationships and wave characteristics can be investigated using slinky type springs. The following are just a few of many options.

Investigating the relationship between speed and amplitude:

  1. Have the students stretch the slinky spring about 5 feet between them so that their hands are touching the floor and the slinky is laying sideways stretched out on the floor.
  2. Have the students mark the floor with masking tape where the ends of the spring are
  3. Have the students practice making pulses with different amplitudes from one length of the spring to the other
  4. From the center of the masking tape on the floor, mark 10 centimeter intervals going one direction perpendicular to the length of the spring
  5. Have students measure the amount of time it takes for the pulse to travel down the slinky and back making a 10 cm pulse
  6. Repeat the last step three times to get three results to average
  7. Then increase the amplitude to 20 cm and time three trials
  8. Continue to increase the intervals until 60 centimeters
  9. There should be no relationship between amplitude and speed

Investigating the relationship between tension of the spring and speed:

  1. WARNING: it is easy to exceed the elastic limit of the slinky will performing this experiment make sure the students are aware of this and discuss that over stretching the spring will cause it never to go back to it’s original shape
  2. Have the students stretch the slinky 2.0 meters between them
  3. Start a pulse in the slinky and measure the time it takes for one pulse to travel the length of the spring, repeat measurements twice more for accuracy
  4. Make sure to have the students record their data in a data table
  5. Next stretch the slinky 2.5 meters between the students and time a pulse three times
  6. Continue until students have reached 5.0 meters
  7. Have students calculate speed by using v = distance pulse traveled/time it took for pulse to travel
  8. Graph length vs. speed
  9. As tension increases, speed increases

Does mass or energy get transferred in wave motion?

  1. Have students tie some brightly colored string to various parts of the slinky
  2. Stretch the slinky out between the two students on the floor
  3. Have one student make a pulse and have the students observe what happens to the pieces of string, do they travel with the wave, or do they just jiggle back and forth?
  4. The string jiggles back and forth, therefore mass, not energy is transferred

Verifying v = fλ; for a standing wave:

  1. This experiment is tricky to do if students are sloppy with their measurements, but it is possible to get very accurate data
  2. Have students stretch a slinky spring on the ground between them 4 meters apart
  3. Mark the ends of the slinky with masking tape
  4. Have one of the students holding the end of the slinky shake it so that a standing wave with one anti-node is produced
  5. Have the students time 10 cycles and record their data in their data table
  6. Now have the students produce a standing wave with two antinodes and record the time it take to complete 10 cycles
  7. Have the students repeat this process, getting as many standing waves as possible set up on the spring. The high end of possibilities is usually around five antinodes
  8. Have the students find the wavelength of each standing wave in the following way. If one anti-node was made, then ½ of a wavelength covered 4 meters, so the wavelength of the wave was twice that or 8.0 meters. For two anti-nodes the wavelength is 4 meters, for three antinodes the wavelength is 8/3 of a meter, four antinodes is 2 meters, etc.
  9. The number of cycles in one second is the frequency of the wave, so have the students take the number of cycles (10) and divide that by the amount of time it took to complete those 10 cycles
  10. Then have the students multiply each wavelength by it’s corresponding frequency for that trial. The students should get approximately the same speed.

Reinforcement Activities
Make easy to see, slower moving longitudinal and transverse waves using a Longitudinal Wave Model or a Transverse Wave Motion Model or A complete Wave Motion Demonstrator and Longitudinal Wave Demonstrator.

Have students study standing waves using a String Vibrator, or a Standing Wave Demonstrator.

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