## Thursday, January 16, 2014

### Balanced Balloons - a new Figuring Physics

I am delighted to have developed some "Figuring Physics" ideas for The Physics Teacher columnist, Paul Hewitt over the years.

If you want a treasure-trove of Hewitt's "Figuring Physics" (a.k.a. "Next-Time Questions"), you're in luck.

Hewitt's Next-Time Questions at Arbor Scientific

We're in the midst of our study of electrostatics. Usually this brings torrents of rain to Northern California. This year's drought seems to be impervious to my machinations.

In any case, this little puzzle came to mind. It was preceded by the developments of Balancing Charges 1 and Balancing Charges 2 PhyzJobs. But I turned the concept into a standalone puzzle.

We begin with two helium-filled balloons that, when oppositely charged, are exactly balanced. They are attached to a massless bar that has a frictionless hinge at its midpoint.

I'll post the answer in the comments next week. It's a fun one to think through. Maybe it will make the cut for next year's round of "Figuring Physics."

Hewitt’s Figuring Physics cartoon column appears in different journal, and his abstract cartoon series of Next Time Questions is planned to encourage student reflection on physics at home between physics classes. I deeply welcome opportunities to develop my students’ attention spans—to reflect at length on problems that could be nontrivial and have need of extended thoughtfulness and patience.

Anonymous said...

Neutralizing the pink balloon would involve adding electrons, leading to the scale tipping toward the pink balloon - Making choice A correct.

Neutralizing the blue balloon would involve removing electrons, leading to the scale tipping toward the pink balloon - Making choice B correct.

Neutralizing both balloons would add electrons to pink and remove them from blue, leading to the scale tipping toward the pink balloon - Making choice C correct.

Therefore, D, all choices must be correct.