What is inertia?
An object that is not moving (at rest) stays at rest until a force acts on it. A moving object keeps moving until a force stops it. This is called inertia.
The paper cup tower
You need four heavy paper cups and three sheets of paper. Work in groups of three.
- 1🥤 Build the tower
Put a cup upside down on the table, a sheet of paper on top, then another cup, and so on, until you have four cups.
- 2💨 Pull the top sheet out — quickly!
Pull it out sideways in one fast movement.
- 3🔁 Repeat with the other sheets
What happens to the cups each time?
If you pull fast, the cups stay where they are because of inertia, and then gravity pulls them down onto the cup below. If you pull slowly, the friction of the paper drags the cups with it and the tower falls!
The scientist Isaac Newton described the law of inertia in the 17th century. It is also called Newton's first law of motion.