This post is part of a series of static electricity activities. Check out the whole series! For a brief discussion of static electricity basics, check out the first post.
Static electric force is strong enough to hold a balloon on the wall and not much else. But when you take this small force and apply it to even smaller stuff things get interesting.
You can use static electricity to separate a mixture of salt and pepper. You will need a balloon (a plastic comb or ruler works too), a plate and of course, salt and pepper.
Mix about a teaspoon of salt and pepper together on the plate.
Rub the balloon on your head (or a wool sweater or your dog or something else fuzzy) so that it is good and loaded up with electrons.
Hold the balloon a couple of inches above the salt and pepper mixture and watch what happens! You should see the pepper jump off the plate and on to the balloon leaving the salt behind.
There are two reasons the pepper sticks to the balloon and the salt does not.
First, the pepper polarizes much easier than the salt. That is, its electrons move mostly to one side of the pepper flake leaving one end positive and the other negatively charge. The positive end is attracted to the negative balloon. Salt does not polarize quite as much so it doesn’t feel as much of a pull. However it will jump up on the balloon if you hold it very close to the plate.
Second, the pepper flakes are much lighter than the salt crystals. So even if the salt does jump up on to the balloon, it is too heavy to stay and falls back down.
You will also see some of the pepper and salt jump up to the balloon and then fly off. This is because it grabbed an electron off the balloon and suddenly became negatively charged – just like the balloon. The like charges repel, throwing the tiny particle away.
See what happens when you hold a charged balloon next to other small particles. Try gelatin (it makes tiny towers!), sugar (granulated and powdered), baking powder, cinnamon and anything else you might have in your spice cabinet. Which particles are attracted to the balloon and which are not?