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CAN BUOYANCY BE MEASURED?

We have experimented with a coffee can filled with water, held by twine, and dipped into a container of water to see if the weight feels any different when it is in the water than it feels when it is out of the water. We learned that buoyancy makes it feel lighter.

We know that sometimes our senses tell us something that isn't quite true. Especially if we just use one sense, as when we dipped the coffee can. Now, we're going to measure the difference, by hooking the other end of the twine (the "tail end") to the spring scale. After we do this, we will know if our sense that told us the can felt lighter was telling us the truth.

How about that? It really is lighter, isn't it? The buoyancy of the water pushes up on the can enough to make an actual difference in the weight of the can! Wow!

Now, we're going to do the same thing with this large rock. (It is important that we remember to call it a rock. Some people call small rocks "stones," but that is not correct. Stones are like diamonds and rubies.) So we weigh the rock before putting it into the water, and weigh it while it is in the water (not all the way to the bottom, of course).

We are going to do these same experiments again, only this time we will dip the can and the rock into salt-water solution and see if it has more or less, or the same amount, of buoyancy as plain water. We can do it with sugar-water, as well.

Buoyancy is fun!

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