I first became interested in rock stacking during our trip to Technorama, the Swiss Science Center. Thorsten Künnemann, their Executive Director took us on a marvelous tour of Zurich. As we walked along the shore of Lake Zurich, we came to an area that was filled with amazing stacks of balanced rocks. When you first see them, you think that they must be held together with glue or mud. Only when you get very close can you see that it is all a matter of balance. Since then, we have seen similar stacks in other places and made some of our own.

If you would like to try rock stacking, you will need:

• a flat, stable surface
• a variety of rocks or other things to stack
• steady hands
• lots of patience

While at first rock stacking may seem like a frivolous activity, there is actually quite a bit of science and engineering involved. As we saw in the Science of Balance video, we can balance an object by keeping its center of gravity (its balancing point) directly above its base (the part of the object that is supporting it.)

To start, you need a wide variety of rocks, or other objects to stack. If you don't have lots of large rocks, you might try stacking toys, stuffed animals, or other irregularly shaped objects that are not breakable.

Select a large, steady rock as your foundation. You want the rock on the bottom to be very stable, because if it wobbles, your entire stack will wobble, which usually means that it all falls down. By using a wide, flat rock, it has a large base, which gives you plenty of working room to keep the center of gravity inside that base. While you are learning the art of rock stacking, you will have better success if you also choose a foundation rock that has a fairly flat top, to make it easier to balance the next rock.

It is easiest if you start simply, using fairly flat rocks to make stacking easier. Keep in mind that as you add each rock, you are adding pressure to the rocks under it, which may shift their center of gravity. Work slowly. Instead of putting a stone in place and releasing it, gradually let its weight rest on the stack, checking to see whether the stack remains stable.

Once you have the knack of stacking flat rocks, then you can start to get more creative and adventurous. Use rocks with unusual shapes, and try balancing them on smaller bases. Remember that a smaller base means you have to be more careful with the stack's center of gravity. Also remember that each rock can change the center of gravity of the entire stack, throwing the stones below it out of balance. If one orientation is unstable, try turning the rock to a different side. If that does not work, then try a different stone. The more you practice; the more you will learn about the art and science of stacking rocks.

Three Holes
This week's experiment will give you some good practice at thinking scientifically. The experiment itself is very simple, but as with many simple things, the more you think about it, the more you will see. To try this, you will need: - a two liter soft drink bottle - pliers - a sharp nail - water First you need to empty the two liter bottle. I highly recommend using the soda to experiment with making the perfect ice cream float. Once the bottle is empty, rinse it and remove the plastic label if it has one.
We want to make three holes in the plastic bottle, each at a different depth. Holding the nail with the pliers, make a small hole about one inch up from the bottom of the bottle. I found that twisting the nail back and forth as you push makes it easier to start the hole. You want the hole to be round and as smooth as possible. Be careful not to tear the plastic (or your skin!) Once you make the hole, wiggle the nail around a bit to help make the hole round.
After you make the first hole, make the second about half way up the bottle, and slightly to one side. You want all three holes to be as close to the same size as possible, and you do not want the holes to be directly above each other. The third hole should be about an inch or so below the point where the top of the bottle starts to narrow, and again a little to one side. The photo on the right shows approximate locations.
Place the bottle in the sink, under the faucet. Fill the bottle with water, and leave the water flowing just enough to keep the bottle full as the water flows out of the three holes. We want to compare how far each stream of water goes, which is why we did not want one hole directly above another. We want to be able to see the three streams easily. Now you should understand why we are working in the sink, to keep from making a mess.

Before you actually try this experiment, take some time to think about it. Once the bottle is full, water will be flowing out of all three holes. If you measured how far each stream of water moved away from the bottle before it hit the bottom of the sink, which stream of water would hit the farthest away? Which stream would hit the closest? Why? Keep in mind that there may be more than one thing to consider in how far the water reaches.

Once you have spent enough time thinking to have a good idea of what will happen, turn on the water and try it yourself. Next week, we will look at the results, and figure out why it worked the way it did.

Have a wonder-filled week!

Go to Part 2.

Well, last time I left you with a challenge. If you have two metal rods (straightened paper clips) and one of them is magnetized, how to you find out which is which, without using anything else? To find out, you will need:

- steel wool
- a sheet of paper
- the two paper clips we used last time (or you can make two new ones)

I know that I said you could not use anything else. The steel wool is for later, to help explain what is happening. Pick up the two paper clips and bring the ends together. They should stick if they are still magnetized. OK, so which one is the magnet? To find out, we need to do something different. Bring the end of one paper clip near the middle of the other paper clip. Does it stick? If it does, then it is the magnetized clip. If it does not, then bring one end of the other paper clip to the middle of that one. The magnetized clip will stick to the middle of the nonmagnetized clip. The nonmagnetized clip will NOT stick to the middle of the magnetized one. Why?

Place the magnetized clip on a sheet of paper. Hold the steel wool over the clip, grab the two ends of the wad of steel wool and rub them against each other. Tiny bits of steel wool should fall onto the paper, and you should notice that they are sticking to the paper clip. Pay close attention to where on the paper clip they stick. The ends, right? That is where the magnetic pole is, and it is where the magnetic field is strongest. The middle of the paper clip has almost no magnetic field at all, so the steel wool does not stick there.

Now you know why the nonmagnetized clip would not stick to the middle of the magnetized clip. The magnetic field in the middle was not strong enough to attract it. On the other hand, the end of the magnetized clip will stick to any part of the nonmagnetized clip.

Not at all hard to figure out, once you know the science.

This week's experiment is a fun science puzzle involving magnets. To try
it, you will need:

- a strong magnet (available at most hardware stores)
- three paper clips

Straighten two of the paper clips, so that you have two long, fairly straight
pieces of wire. Get both as straight as you can. Place one aside. Hold
the other, and rub one end of the magnet along the paper clip, starting at
your finger, and moving to the other end. Move the magnet away from the metal
and repeat the process. Keep stroking the magnet along the paper clip, always
in the same direction, for about 40 strokes. By doing this, we are
magnetizing the paper clip.

Test the magnetized paper clip by bringing one end of it near the extra paper
clip, the one that you did not straighten. If your paper clip is magnetized
enough, it should attract the other clip. If not, try again with the
procedure above.

Once you have the paper clip magnetized, you are ready for the challenge.
Put both of the straightened paper clips together. Mix them until you are not
sure which is which. The challenge is to figure out which one is the magnet
and which is not, but you cannot use ANYTHING else to test with. No fair
using the third paper clip, iron filings, a compass, or anything else. You are
also not allowed to break the paper clips. The two straightened clips are
all you need to figure it out.

So, how do you find out which is which? If I told you, you would just say,
"Oh that makes sense." instead of really trying it. If you are really
patient, you could wait until next week for the answer, but I bet you have
enough scientific curiosity to actually get the materials and try it yourself.

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This experiment comes from a question sent in by a list member who wanted to know how a drinking straw works. At first this seems to be a very simple thing, but like most very simple things, the more you try to explain it, the more complicated it gets. To explore this subject, you will need:

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This week's experiment is one that we used for teaching about birds back when I worked in the Education Department at the Memphis Pink Palace Museum. On our trip, we went by to say Hi to old friends, which brought back tons of great memories. This is one of the fun things my brain dredged up.

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I thought this week we would do something on judging distances. If you look at the faces of different animals, you will find that their eyes are placed differently. Some have both eyes in the front of their face, like ours. Others have their eyes on the sides of their heads. Why? We can do an experiment to learn at least one reason for this.

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This week's experiment seems to be a magic trick, but the basic idea is very useful. It is the idea behind the self sealing tires that seal themselves after you run over a nail. To try this, you will need:

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This experiment comes from a series of news spots that I saw regarding the spring equinox. The equinox occurs on the day when winter changes to spring and when summer changes to fall. There is a persistent story that during the equinox is the only time that you can stand an egg on its end. I did a news search and found hundreds of articles from newspapers and television with stories about this. In reality, the equinox has nothing to do with it and your chances of standing an egg on its end are the same all year round.

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When is a glass full of water really full? You may be surprised at how much you can add to a full glass without overflowing the water.

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The experiment this week comes from spending too much time in hotel rooms as I travel. As I was packing for the trip home, I found it very useful for adjusting the television when I was not directly in front of it.

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This project has science fair potential.

Electrostatic fields can do some very interesting things. This is a simple trick that you can do almost anywhere, as long as you carry a balloon in your pocket.

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This experiment is actually more math than science, but it is such a surprising demonstration that I decided to include it. It is really very simple, once you think about it, and all you need is:

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Don't let the title fool you. This experiment does not involve any explosions. Instead, we are going to explore the science of resonance. Resonance involves putting in small amounts of energy, at just the right time, to get more effect. A good example is pushing a swing. Each push causes the person in the swing to go higher. We will lift a phone book high into the air by blowing on it.

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