3 - 8/2/2005 3: PROPERTIES OF WAVES Definition of Wave A...

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8/2/2005 P108 Lab 3: page 1 3: Definition of Wave A wave is a disturbance traveling in a medium . A. S MALL G ROUP A CTIVITIES WITH S LINKIES Several basic properties of wave behavior can be demonstrated with long springs and slinkies. Quite a bit of work will be done in this class with springs and strings because you can see the waves on a spring, which you can’t do with sound waves. You study of sound will be easier for you if you can learn to make analogies to other kinds of waves which you can visualize. 1. Wave Propagation and Reflection Have one person hold one end of the spring and another person hold the other end. Stretch the spring until it is 15 ft long. One person should send pulses down the spring by jerking the spring to the right and back to center. Do this very fast, to make the pulse as short as possible, but try not to overshoot when you bring your hand back to the center. The pulse should be only on one side: This Not This Be sure that you understand why this is a wave which you are creating. What is the medium in this case? What is the disturbance? Is the wave transverse or longitudinal? All waves have the property that they can be reflected from boundaries. Waves are reflected different ways from different types of boundries. What happens to the pulses when they are reflected from the fixed end? 2. Speed of a Wave
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P108 Lab 3: page 2 Many important properties of sound depend on the speed at which it travels through the air, so it is important that you know what speed is and how to calculate it. Speed is the distance something moves in one unit of time. The easiest way to measure speed is to measure the time it takes it to travel a known distance and then divide the distance by the time. Speed = distance/time . Have a third person use a stopwatch to measure the amount of time it takes for a pulse to go down and back once. It may take several tries to get a good value for the time. Calculate the speed of the wave . Remember, distance = 30 ft! (15 down, 15 back.) How far does this wave travel in one second? How far would it travel in 15 seconds? 3. Wave Speed Depends on the Medium Stretch the spring out to 20 ft., and once again send pulses down the spring. From casual observation, does the pulse travel faster or slower than before? Measure the speed with the watch. 4. Is there Reflection from a Free End? Tie a long string (10 ft. or more) to the end of the spring. Tie here Hold here Before you send pulses down the spring, predict what will happen to the pulses when they hit the string. Will they be reflected, or disappear, or what? (The spring/string junction is called a “free end” because the string allows the spring back and forth freely. Since this is a transverse wave, only the back-and-forth direction matters as far as the wave is concerned.)
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P108 Lab 3: page 3 Now try it. What happens? Draw sketches showing how this is the same or different from when the wave hit the fixed end.
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This note was uploaded on 01/20/2012 for the course PHYSICS 108 taught by Professor Kesmodel during the Fall '08 term at Indiana.

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3 - 8/2/2005 3: PROPERTIES OF WAVES Definition of Wave A...

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