More crazy ideas

by Stephanie Chasteen on February 12, 2009

Session:  Eugenia Etkina - Pedagogical Content Knowledge

Session: Eugenia Etkina - Pedagogical Content Knowledge

Look at this picture.  What will happen to the balloon when we push the cart forward, and why?  (Don’t watch the video first — come up with ideas and reasons first).

Balloon in box

Balloon in box

Make as many predictions, and reasons, that you can, even if you don’t believe them all.
Remember that coming up with the right explanation isn’t the important thing – it’s coming up with ideas that are testable.

Now watch the video and see what happens.

If you have trouble understanding why it does what it does, make a note in the comments and I’ll answer you.  (I don’t want to short-circuit your thinking by telling you the answer here).

I just love this stuff — what good ways to get students thinking and reasoning.


habber24 February 17, 2009 at 8:21 pm

So I don’t exactly know why this happens, but I think it has something to do with the air pressure in the box relative to the helium pressure in the balloon…. Am I on the right track??

sciencegeekgirl February 18, 2009 at 4:05 pm

Yes, you’re totally on the right track!

sciencegeekgirl February 23, 2009 at 6:28 am

Think about it this way… if the box had several ping-pong balls on the floor of it, what would happen to them as the box moved forward? Well, the same thing happens to the air. Does that help?

habber24 February 24, 2009 at 6:11 pm

Yeah, I was thinking that… So does the air move to the back of the box, creating a higher air pressure in the back, which would promote the balloons movement forward??!!

sciencegeekgirl February 28, 2009 at 6:41 am

Yup, that’s how I understand it!

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