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MAKING WAVES

Has anybody ever said, "Don't make waves," when they wanted you not to complain? Well, we're going to make waves, but it won't be the kind of waves you make when you complain.

We have a 50-foot clothesline tied to a post. One student should walk to the end of the clothesline, holding it tightly, and pulling it as taut as possible. Another student
should tap the post with a hammer. The student with the free end of the clothesline will be able to feel the waves.

It could be timed: using a stopwatch, start it when the hammer hits the post, and stop it when the other student says he or she can feel the wave. The student with the hammer could even tap out a rhythm, and see if the other student feels the rhythm.

What's happening here? The energy from the hammer is being transmitted along the rope by longitudinal (say, "lon-ji- tood-in-al") waves.

When the hammer is tapping lightly, it will make longitudinal waves of low amplitude; heavy tapping makes longitudinal waves of high amplitude.

When the hammer is tapping slowly, it will make longitudinal waves of low frequency; rapid tapping makes longitudinal waves of high frequency.

The student with the free end of the clothesline should walk a couple steps closer to the post to slacken the clothesline, then move it up and down. The waves you see now are called transverse waves.
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How easy is it to detect each kind of wave?

Tie another rope to the post, and make each kind of wave. How can you make both longitudinal and transverse waves with equal frequencies? Try it.

Note: Longitudinal waves -- e.g., sound waves -- travel in a back and forth movement in line with the particles that produce them. Transverse waves -- e.g., electrical waves, radio waves, and all electromagnetic waves -- move at right angles to the direction the wave is traveling.

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