Link to Whistle Stick, part 1

I hope that you made your own Whistle Stick, and have been playing...., I mean experimenting with it. I also hope that you spent some time thinking about the science behind the sound that it makes, because that is what we are going to explore this time. For your exploration, you will need:

- a wooden spoon
- a large container of water
- the Whistle Stick from last week

It's always good to start with the basics, so begin by thinking about sounds in general. We hear a sound because of waves traveling through the air. Just as dropping a stone into a pond causes waves to spread out across the water, popping a balloon, vibrating a guitar string, or singing a song causes waves to spread through the air. When those waves hit our ear drums, we hear the sound. That means that the Whistle Stick must be producing waves in the air. But how? That is where the wooden spoon comes in. We will use it in place of the popsicle stick, and look at waves in water instead of air. Hold the wooden spoon between your palms, with the end of the spoon in a container of water.
Slide your palms to twirl the spoon slowly in the water. As the spoon spins, it makes waves in the water. Try spinning it at different speeds, noticing how that changes the distance between the waves. What you should notice is that as the spoon twirls, it pushes on the water to send out a wave. As you spin the spoon faster and faster, it makes more waves, and those waves get closer and closer together.
Now lets think about sound waves. The picture at the right shows a graph of the sound produced by the whistle stick. Notice that at the start of the sound, it reaches far up graph. The higher up the graph it goes, the closer together the sound waves are, and the higher the pitch of the sound. If you click the picture, you can watch a short video, letting you hear the sound, seeing how the changing sound matches the graph.
It is much easier to see (and hear) if we slow things down. This graph shows the same sound, stretched out four times longer than the original. That lets us see the curve as the pitch falls. Again, you can click the picture to watch a short video. Because it plays the sound slower, it is easier to see (and hear) that the sound begins with a high pitch (waves very close together), and then the pitch falls as the waves get farther apart.

Now lets put that all together. Like the wooden spoon, the faster the popsicle stick spins, the closer together the waves will be, and the higher the pitch of its sound. When you first snap your fingers, the Whistle Stick spins very fast, making a high pitched sound. As it pushes against the air to produce those waves, it gives up some of its energy of motion. That causes it to spin slower, producing a lower pitched sound. Looking at the graph, we can see that the rate of spin slows very quickly at first, and then more gradually.

If you remember from last week, I also made a Whistle Stick from a tongue depressor that was much wider. it made a much lower pitched sound, that did not last nearly as long. Why? The wider blade had to push against more air, transferring the energy of motion much faster, causing the speed of its spinning to drop much faster.

If you want to do some experimenting, you might try cutting notches into the sides of the stick or doing other things to change its shape. Do you think that would change the sound? Sounds like a good reason to eat more popsicles to me.

This experiment is one that I have noticed while doing my electricity shows. I use a balloon in the show to demonstrate positive and negative static charges. While holding this balloon, I noticed that I could feel a variety of sounds.

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This week I have been getting quite a few questions about the earthquake that causes the devastation, so I thought we would experiment a bit to help you understand more about them. You will need:

a wooden pencil
a large, zipperlock, plastic bag
water
a large plate
cake
Jello or other gelatin

Several people wanted to know why this earthquake produced a tsunami when most earthquakes do not. To understand that, we need to know about faults. Before you start listing all my faults, such as forgetting to include parts of the experiment, I am talking about geologic faults. Imagine the rocks in the Earth as a wooden pencil. If you hold the ends of the pencil and push upwards on the center with your thumbs, the pencil will bend slightly and then suddenly break. When pressure causes the same thing to happen in the Earth's crust, the break is called a fault.

There are different kinds of faults, depending on the direction of the pressure. Hold your hands in front of you, side by side, with the palms up. Imagine them as the rocks on either side of the fault. If you move one of your hands away from you, you can simulate a strike slip fault. This is a very common type of fault. A good example is the San Andreas Fault in California. Because the sides of the fault move horizontally, this type of fault often results in fences and roads that are broken, with one side shifted several feet to the right or left of the other.

While strike slip faults are common, there are other ways that the rocks can move. If the pressure of the sides is towards each other, then one side is forced upwards, causing a thrust fault. If the pressure is away from each other, then one side can move downwards, forming a gravity or normal fault.

That kind of fault has a big impact on the formation of a tsunami. Fill a large zipperlock bag half-full of water. Seal it well, and work over the sink, just in case. Hold your hands in front of you as you did before, with the bag of water laying on your palms. Watch what happens to the water when you slide one hand away from you, simulating a strike slip fault. You should not see much movement of the water. Next, move one hand upwards quickly to simulate a thrust fault. You get a lot more movement as the water rushes from the lifted hand to the lower hand. You get the same sort of rush if you lower one hand, as in a gravity fault.

The recent earthquake was produced by a thrust fault, which caused a similar surge in the water of the ocean. That surge produced the waves that caused the destruction. Be sure to do the experiment over the sink. I carried mine into the den to show my Mom how it works. The zipper was not completely sealed, and I produced a tsunami on the floor.

I hope that this will help you understand some of the science behind this event. My thoughts are with all those that lost loved ones in this disaster.

Have a wonder filled week. 

For part 2 (using the cake and jello) go to: http://thehappyscientist.com/science-experiment/richter-scale

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