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Experiments With Inertia & an Egg

In space---where there is no air---a spinning satellite will spin indefinitely until something stops it, such as another satellite or debris striking it. This physical property is called inertia, the tendency of objects in motion to stay in motion unless acted upon by an outside force. Inertia also covers objects at rest, which remain at rest unless something makes them move, such as a hand or motor. Inertia also applies to objects on Earth, but outside forces such as the friction of an object against a surface or even the air can slow down its movement.

Egg Drop
- Set an aluminum pie pan face-up on top of a glass of water. Place an empty toilet paper tube on top of the pie pan, lining up the tube so it is directly above the glass. Place an egg, hard-boiled or uncooked, carefully on top of the tube. To drop the egg into the water, slap the pie pan horizontally so that the pan clears the glass without knocking it down. The tube also moves, but the egg falls directly down into the water. When the egg is on the tube, it remains at rest because of its inertia until acted upon by an outside force. In this case, that force is gravity, which pulls the egg downward when the tube and pan are knocked out of the way.
Spinning Egg
- Obtain several hard-boiled and uncooked eggs without knowing the identify of each. Spin an egg on its side on a glass plate. Lightly touch the egg on the top until the egg stops spinning and then release your finger. Observe what happens with the egg. Repeat with the other eggs. A hard-boiled egg will not start moving again once it is stopped. An uncooked egg, however, will start spinning again when you remove your finger. When you stop an uncooked egg, the liquid contents continue to spin due to their inertia. The force of the spinning liquid causes the entire egg to move again when you release your finger.
Egg Toss
- Two people hold a sheet between them with the bottom part curled upwards. Throw an egg at the sheet as hard as you can. The egg hits the sheet and slides down to the bottom without breaking. Now throw an egg at a brick wall. The egg, of course, breaks. In both cases, the inertia of the thrown eggs tends to keep them in motion until acted on by an outside force such as the wall or the sheet. This experiment also demonstrates the concept of momentum, which is related to both the mass of the egg and its velocity.
Egg Shell and Knife
- Hold a sharp kitchen knife with the point facing upwards and balance half an eggshell on top. Try to puncture the egg shell by tapping the handle of the knife on a counter. The egg shell does not break. Now hold the knife loosely and let it drop onto the counter, keeping your hand curled lightly around the handle. The shell breaks. Inertia plays a part in this experiment, because in both cases when the knife moves downward the inertia of the egg shell keeps it moving downward. In the second example, however, the knife is allowed to bounce upward which pierces the shell as it continues to move downward.

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