Experiment

Why does this happen? To help figure it out, we tried a few tests. We observed that when the lemon was in the water, it started to roll as soon as the coin was placed on it. When it rotated beyond a certain point, the coin fell off.

First we took the lemon out of the water and put it on the table. It was fairly easy to get the coin to balance. On the table, the lemon didn’t roll and the coin stayed put.

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So we put the lemon back in the water. Instead of a coin, we tried a scrap of paper. The lemon didn’t roll, and the paper remained on top.

We wanted to see what would happen if the coin were attached to the lemon. We cut a small slit through the lemon skin and stuck the coin in. We put the lemon in the water with the coin pointing up. It rotated so that the coin was on the bottom, and as it turned, the lemon sank to the bottom.

What do you think is going on? Why did the coin slip off the floating lemon? Are there some other tests that you might try?