Elliot and the Surfing Scientist: Floating ping pong ball

Posted 18 May 2022Wed 18 May 2022 at 5:47am

Hand holds a ping pong ball in a glass upside down in a fish tank full of water — Elliot and the Surfing Scientist: Floating ping pong ball

ELLIOT: Wow. Check out the viscosity of this viscous liquid.

RUBEN: Have you been drinking Vitamin B again, Elliot?

ELLIOT: Yeah. What should I do with it?

RUBEN: Leave it on the shelf. Looks cool.

ELLIOT: Now it's time to Beat the Conundrum with some lateral thinking. What's the problem, Ruben?

RUBEN: The problem is the Floating Ping-Pong Conundrum.

ELLIOT: Do you mean ping-pong as in… 'Whoa'?

RUBEN: Yes.

ELLIOT: Really?!

RUBEN: No, of course not. I mean, ping-pong as in table tennis, as in…

ELLIOT: Aha.

RUBEN: Here is a ping-pong ball. Here it is floating on some water. If I put a glass upside down over top of the ping-pong ball and then push the glass right down to the bottom of the aquarium, where do you think the ping-pong ball will float? At the bottom, in the middle or at the top of the glass?

ELLIOT: Hm, OK. Tricky!

RUBEN: Would you like ten seconds of thinking music, Elliot?

ELLIOT: Yes, I would. Thank you very much for asking.

RUBEN: Let me get my Irish tin whistle and play you some.

ELLIOT: OK. I wish he would stop. OK. So we've got a little bit of air pressure.

RUBEN: That's your ten seconds.

ELLIOT: OK. I think it is going to float higher in the glass.

RUBEN: Well, let's see, shall we?

ELLIOT: Yep.

RUBEN: So we put the glass over the ping-pong ball and down we go.

ELLIOT: It's staying in the same position. It hasn't really moved at all. Nothing has changed.

RUBEN: Exactly. And let's come all the way back.

ELLIOT: So why is it doing that?

RUBEN: Well, Elliot, good question. Inside that glass, there is air. When we started, that air inside was at atmospheric pressure, which is actually quite strong. As you push down, that air is also pushing down on the surface of the water inside the glass, which keeps the surface of the water at the bottom of the glass so the ping-pong ball floats there as well. It can't come to the top because the surface is at the bottom.

ELLIOT: So the pressure is the same as out here?

RUBEN: Exactly.

ELLIOT: Aha! You know what I've learnt?

RUBEN: What have you learnt, Elliot?

ELLIOT: Be like a ping-pong ball. Don't let the pressure get you down.

RUBEN: Mm.

ELLIOT: Game of ping-pong?

RUBEN: Yeah, I'd love one.

ELLIOT: Alright.

RUBEN: Out.

ELLIOT: (Sighs) Good game, good game.

RUBEN: Thanks very much.

SUBJECTS: Science

YEARS: 3–4

A ping pong ball usually floats on the surface of water.

Watch what happens to a ping pong ball in a tank of water as Ruben Meerman, the Surfing Scientist, experiments with air pressure.

Things to think about

1.What happens if you push a ping pong ball underwater and release it? What do you need to do to keep the ping pong ball underwater?
2.Ruben holds a glass (upside down) over a ping pong ball that is floating on the water's surface. He asks what will happen when he pushes the glass towards the bottom of the tank? Use the 10 seconds think time to predict what will happen. Where in the glass does Elliot think the ball would float?
3.During the experiment, what holds the ping pong ball underwater? Why doesn't it float to the top of the glass? Try the experiment yourself. Where does the water level stay in the glass? Why does this happen? Think about what Ruben said about air and how it pushes down on things.
4.Draw a picture to show the experiment and explain what happened and why.

Production Date: 2008

Copyright

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Posted 18 May 2022Wed 18 May 2022 at 5:47am