Have you ever seen the magic trick where someone yanks the tablecloth off a table, and all the dishes and silverware stay in place? Well, it’s not magic - it actually happens because of inertia! Inertia is a physical property of all objects. Because of inertia, a thing will stay at rest (or keep moving how it’s moving) unless it’s pushed or pulled by something else. Otherwise, it’ll stay put, like all the dishes and silverware on the table.
This slow-motion demonstration has way less potential for a plate-breaking mess, and it’s an amazing way to see inertia in action. Try it out!
How we did it:
- crate box
- dowels (4)
- rubber bands (4)
- golf ball
Gather your materials.
Cut the legs off of a pair of pantyhose, then stretch the remaining piece into a rectangle about the size of the crate box.
Stick a dowel into each corner of the crate box.
Push a rubber band about 2 inches down onto each dowel.
Stretch each corner of the pantyhose to a dowel and double knot it.
Place some sequins in the center of the trampoline.
Have a friend or parent point the smartphone at the trampoline, and set the camera app to slow motion mode. Start recording, then drop the golf ball in the center!
Watch your slo-mo video. What do you observe?
When you slow down the footage, you can see that the sequins float in midair for a moment. That's because of their inertia! The falling golf ball pushes on the trampoline, but it doesn't push the sequins. Because there's no push or pull on the sequins, their inertia keeps them at rest exactly where they were.
After a second, the sequins start to fall because of the force of gravity. At about the same time, though, the trampoline springs back up like a rubber band and collides with the falling sequins. That does give the sequins a push - one that launches them up into the air!