401px-drinkingstraws.jpgThis is a great little activity from Eric Muller’s While You’re Waiting for the Food to Come.

Get a plastic drinking straw, in its wrapper. Unwrap one end, so the straw is still wrapped in the paper, and then slide the wrapper quickly up and down over the straw, until the straw and wrapper feel a little warm.

Take off the wrapper and the straw will stick to the palm of your hand!

For extra fun, do this with a friend. Ask them first if they’re attracted to you or repulsed by you! Then both do the straw-thing, and hold the straws near one another (you’ll find that your friend is repulsed by you).

You can find a writeup of this activity on Eric Muller’s website.

Why does this work? The straw ends up negatively charged (it’s got just about 40 nanocoulombs of charge) after being rubbed with the paper. Since like charges repel, it will repel the other straw. And charged objects attract neutral objects, so it sticks to your hand.

This is the same principle as the old rub-the-balloon-on-your-head-and-stick-it-to-the-wall trick.

Here is a simulation you can play with that shows you the physics of this sort of trick.