Potato Plummet
save
It's a famous parlor trick: a magician walks up to a table set for dinner, yanks off the tablecloth, and the dishes amazingly remain in place. It may look like magic, but what you're witnessing is pure physics. The key is to yank the tablecloth quickly enough. Here's how you can try your hand at this feat - without putting your best china at risk.
What you'll need
- 8- to 16-ounce plastic measuring cup
- 9-inch pie tin
- 3- to 4-inch-tall plastic flat-bottomed drinking cup
- Potato (small enough to fit loosely in the measuring cup)
How to play
Place the measuring cup on a tabletop. Center the pie tin atop the measuring cup and center the drinking cup (upside down) atop the pie tin. Then place the potato on the drinking cup.
With a quick jerk, yank out the pie tin. The drinking cup should go with it, and the potato should land in the measuring cup. (If the measuring cup slips during the experiment, choose a rougher surface.)
WHAT'S HAPPENING: The force of friction between the potato and the drinking cup creates a loose "connection" between them. This connection is strong enough to keep the potato atop the cup when you pull the pie plate gently (try it and see). Pull a little harder, and the connection breaks, but not before the potato has moved far enough in your direction to tumble onto the pie tin. Yank hard enough, and the connection breaks so quickly the potato is left in midair (almost where it started) and, thanks to the force of gravity, will drop into the measuring cup. The reason the connection between the drinking cup and the pie tin stays intact longer is because it's stronger, thanks to the potato smushing the two of them together.
