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Make a Crater

Create your own craters, and compare them with those on other planets.

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Scale Model of the Solar System

A simple model for seeing how large the solar system really is.

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Make your own craters, and compare them with photos of the real thing.

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The Speed of Electricity

How fast does electricity travel through your wires?

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Sweet Geology

A tasty way to learn about the different kinds of rocks.

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Planets and Pennies

Want to see how much something would weigh on a different planet?

Last week, I left you with a question. We were imagining fish swimming in a container of water. When I was a child, I was told that you could put the container on a scale, and as long as the fish did not touch the sides or bottom; you would only be weighing the water.

We substituted a brick for the fish, and found that if we lowered it into the water, the scale went up enough to equal the weight of the water it displaced. Then we placed it on the bottom, and found that the scale went up to equal the full weight of the brick.

Now, for the question I left you with. What if you put the brick on a scale, and then submerged both of them in the bucket of water? How much weight would the scale show for the brick?

Hopefully, you spent some time thinking about it. We know that the brick felt lighter when we held it under water, because the water was pushing up on it with a force equal to the weight of the water it displaced. That gives us our clue. If the scale was in the water, with the brick on it, it would show the weight of the brick, minus the weight of the water it displaces.

We can find that, without even putting the scale in the water. If we take the weight of the brick and subtract the reading on the scale when we held the brick under water, we get the weight minus the weight of the displaced water.

But that still leaves one more thing to check, as a couple of clever readers pointed out to me. What if the brick (or fish) were suspended in the water without your hand or anything else holding it up?

Well that would be easy to test if we had a fish, but the closest thing I have is a can of tuna, and somehow I don't think that would work the same way. Instead, lets use a water balloon. After all, a fish, like most living things, is mostly water. If we fill a balloon with water, and put in a tiny bit of air, it should float just at the surface and make a very suitable fish replica.

OK, so what do you think will happen? Think about it another way. What if we left out the balloon, and just added the water? Would the scale show an increase of weight then? Yes, of course it would. Do you think that putting the water inside a balloon would change that? No. What about putting that water inside a fish? No, it would still show up as an increase in weight, and since the water is supporting the full weight of the fish, the scale would show an increase of the full weight of the fish, or in this case, the water balloon.

When I was younger, this experiment would have ended with me throwing the water balloon at my brother or my sister. Now that I am older, I wouldn't do that. They live too far away. Luckily, I am going home to see them this coming week, so I may take advantage of the opportunity to complete the experiment there.

Have a wonder-filled week.

This week's experiment goes back to fishing trips from my childhood. As we caught fish, we put them into a large tub of water. I loved watching them swim around and around. I was told that if you weighed the tub, that it would not register the weight of the fish, unless they touched the sides or bottom of the tub. Was that right? Let's find out.

You will need:

- a bathroom scale
- a bucket of water
- a brick or large rock

Start by putting the bucket of water onto the scales, and recording the weight. Then pick up the brick and hold it under the surface of the water. Don't let it touch the side of the bucket. Look at the scale again. Has the weight changed?

Yes, the weight goes up. So the first part of what I was told was wrong. The tub of water did weigh more with the fish in it, even if they were not touching the tub. Well that certainly makes sense.

Next, touch the brick to the side of the bucket. Did it change? No. Touching the side of the bucket does not cause the weight to change. Again that makes perfect sense. Contact between the brick and the bucket (or the fish and the tub) does not make any difference. OK that makes perfect sense too.

Now, what if you placed the brick on the bottom of the bucket? Would the weight change then?

Don't try it yet. Instead, think about it for a minute. (Hint: Think about why some things float and some things sink.)

Alright, now try it. No, I did not say read what will happen. I said try it.

Did you try it? Good, then I don't have to tell you what happened, right? But, I will anyway. When you placed the brick on the bottom of the bucket and released it, the weight increased. Why?

When you put the brick into the water, you should have noticed that it seemed to weigh less in your hand. That is because the water was supporting part of its weight. The weight that you felt decreased by exactly the weight of the water that the brick displaced. The weight of the bucket increased by the same amount. That was the first weight gain for the bucket.

When you put the brick on the bottom of the bucket, your hand was no longer supporting part of its weight, so the weight of the bucket increased enough to register the full weight of the brick. That was the second weight gain.

Just one more question. What if you put the brick on a scale, and then submerged both of them in the bucket of water? How much weight would the scale show for the brick? You've got a week to think about it, or try it yourself.

Have a wonder-filled week.

Fossils are what got me into science, and I still enjoy finding them. If you live near a place where you can dig for real fossils, you are indeed lucky. If you do not have a fossil site nearby, you can still give the techniques a try. You will need:

- sand
- plaster of paris
- several objects to be "fossils." These can be shells, bones, pieces of wood, etc.
- a smooth sided, disposable, plastic container. I like using a large, plastic cup.
- a mixing bowl
- bamboo skewers or toothpicks

Put enough sand into the cup to fill it 3/4 of the way full. Fill it the rest of the way with dry plaster. Pour the sand and plaster into the mixing bowl and stir it around to mix it.

Put about an inch of the mixture back into the cup. Drop in one or two "fossils" and then add enough of the mixture to cover them. Add another "fossil" and then more mixture. Keep doing this until your container is full.

Now your "fossils" are buried, but the "rock" is not very hard. That is why we added the plaster. Pour enough water into the cup to get the sand wet. You want it to soak all the way down to the bottom of the cup, not just wet the top layer.

Once the sand and plaster mixture is wet, let the container sit overnight. The next day, the sand mixture should have hardened into a rock-like substance. Turn the container upside down and tap it firmly a few times. The "rock" should slide out.

Now that you have your "fossils" embedded in "rock," we want to get them out again. When you are digging real fossils, the rock is often as hard or harder than the fossils. This means that you must be very careful as you dig, so you do not damage the fossil. Paleontologists use a wide range of digging tools. Much of the digging is done with small, delicate tools, ranging from picks like the dentist uses to clean your teeth to pointed splints of bamboo to hammers and chisels, depending on the kind of rock that surrounds the fossil. Our "rock" is similar to a soft sandstone, so we will use bamboo skewers or toothpicks to scrape away the rock. Dig slowly and carefully to be sure that you do not miss anything or damage your specimens. Depending on how hard your "sandstone" is, it may take you anywhere from a few minutes to a couple of hours to excavate your finds.

You can make this exercise as realistic as you want. You can add a bit of tempera paint to add color to the sand mixture. Adding less plaster will make the "rock" softer, while more plaster will give you more of a challenge. For a real challenge, press a turkey or chicken leg bone into some modeling clay to form a mold. Mix some plaster according to the directions on the package and pour it into the mold. When it has hardened, remove it and then break it into several pieces. Let the pieces dry overnight and then bury them in the sand/plaster mixture. Since they are about the same hardness as the surrounding "rock," you will have to dig very carefully. When you have recovered all the pieces, see if you can put them back together.

For even more fun, you and a friend can make a cup of "fossils" for each other. It is much more fun if you do not know what to expect. The thrill of discovery is one of the things that makes paleontology so much fun.