Slinky Waves

 

Difficulty: Easy 1/3

Danger: Safe 1/3

What you need:

• a slinky (the longer the better)
• 2 people

This is part experiment and part demonstration. First, stretch the slinky out but not so much that you ruin its slink. Now we will demonstrate different types of waves. A wave is a disturbance that travels. To see this, have one person shake their hand holding the slinky back and forth once quickly. What did you notice? You should have noticed a wiggle in the slinky start at the person who shook their hand to the opposite end of the slinky. That was a wave, a traveling disturbance in the slinky. Repeat the shake. Notice that the slinky is not moving from one person to the other, it is the disturbance of the slinky that moves. This is what makes it a wave. If it was the slinky that was moving from one person to the other…well than you would just be throwing the slinky at each other and not making a wave.

So the slinky isn’t moving from one person to the next, but it is moving. Repeat the shake and notice how it is moving. The slinky moves side-to-side while the wave moves forward. To put it in science terms, the motion of the rings of the slinky is perpendicular to the motion of the wave. This is what physicists call a transverse wave. The important thing to remember about this type of wave is that the motion of the thing that is waving is not the same direction as the motion of the wave itself. One example would be ripples on a pond where the water is moving up and down but the ripples (which are small waves) are moving along the surface of the water. Another fun example is if you have ever been to a sporting event where the crowd “did the wave.” Usually what happens is a group of people all stand up together and raise their hands in the air and make noise than as they sit down the people next to them repeat their action until you see a “wave” of people standing up and sitting pass through the stands. This is a transverse wave because the people never move from their seat but the wave moves down the row of seats.

The second kind of wave is called a longitudinal wave. To make one of these types of waves have one person bunch up a few rings of the slinky and then release them all very quickly. What do you see? It should look like a few rings bunched together travels down the slinky. Again, it is only the wave that is moving, not the slinky. This time, however, the slinky rings are moving in the same direction as the wave but they don’t move with the wave because the return to their original position. Another example of a longitudinal wave would be if you imagine a bunch of people standing in line and someone pushes the last person in line, what do you think would happen? The last person in line would bump the person in front of him/her and that person would bump into the next person and so on. The people are not really moving but the bumping is.

The experiment in this case is more of an Extra Credit so click below for more fun…

Extra Credit

Now that you know how to make waves, lets see if you can affect them. Change how much you stretch the slinky and see if it changes how fast the waves travel on the slinky. Does it affect transverse waves or longitudinal waves differently or the same?