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Try This at Home: Cup and Coin

Illustrated Concepts

An object at rest will remain at rest unless acted upon by an outside, unbalanced force. Mass is the amount of stuff from which something is made. All objects that have mass obey the Law of Inertia.

What You Need

  • 1 cup or mug
  • 1 playing card or index card
  • 1 coin

What To Do

1. Make sure you have an adult with you to supervise this experiment.

2. Place the cup on a table. Place the playing card flat on the cup. Place the coin on the middle of the playing card.

3. Does the coin have mass? Do you think it will obey the Law of Inertia? Make a hypothesis!

4. Pull the card out from underneath the coin as fast as you can. Make sure to keep the playing card horizontal as you do this. Does the coin slide along with the card or does it fall into the cup? Was your hypothesis correct?

5. Clean up.

What’s Happening

The coin (as well as the playing card, the cup, the table, and you) has mass. Things that have mass follow the Law of Inertia. The coin is the object at rest; it is still before you pull the playing card out from underneath it. You exert a force on the playing card by pulling it. The force of friction created from pulling the playing card is not a significant enough force to move the coin. The force of gravity is responsible for the coin falling into the cup when the playing card is no longer there.

Fun Fact

Roller coasters rely on inertia to keep them moving after using a motor to get up the first big hill!