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DENJIRO: Today I’ll show you a science magic trick with a balloon that you can easily do at home. There’s a coin inside the balloon. When I spin the balloon once, the coin starts rolling inside the balloon. However, even when I stop moving the balloon, the coin keeps spinning.
GIRL: How strange!
DENJIRO: Let me reveal the secret. I was actually cheating a bit. I was making the coin spin by moving the balloon ever so slightly. The inside of a balloon is very smooth, and there’s not much friction between the coin and rubber, so moving the balloon just a bit makes the coin keep rolling without slowing down.
NARRATOR: It’s fun to try because the coin spins more than you’d expect. Try it at home!
DENJIRO: Now I’ve spread a large rubber sheet across a tub. You can recreate something incredible with this rubber sheet. Outer space!
First, I’m going to place in the center a heavy metal ball, which represents the sun. This makes the middle of the rubber sheet sink. You can think of this as outer space being distorted due to the sun’s large mass.
Let me drop a small metal ball on the rubber. It’s approaching the metal ball in the middle. This is the sun’s gravity. Now I’m going to place a metal ball in a large dent and have it represent the sun. Let me roll coins on the rubber and have them represent planets such as Earth and Mars. The coins are spinning. This is the motion of planets. The time it takes for the coin on the inside to make one round, or its orbital period, is shorter. In this experiment, there is friction between the coin and rubber. Therefore, the coin loses momentum as it spins and gets sucked into the middle. However, there is no air in outer space, so rotational energy is not lost. As a result, planets rotate forever.
NARRATOR: If the dent where the metal ball is sitting were to stretch infinitely, it would be a black hole.
DENJIRO: I hope energy will bring you all happiness. Our magic word is "Happy Energy!"