Forces: gravity and friction

Ages 9 to 12 Read alone or together · about 35 minutes

Read together

A force is a push or a pull. Forces can change how things move.

Gravity is the pull of the Earth on everything. It is why a dropped ball falls. Friction is a force that slows things when surfaces rub together.

In 1687, Isaac Newton described how forces and motion are connected. A ball keeps moving unless a force, such as friction, stops it.

Do it

1. Make a ramp from a board and books. Roll a toy car down it and measure how far it goes on the floor.
2. Cover the floor with different surfaces: smooth paper, a towel, sandpaper. Roll again. On which does it go farthest?
3. Drop a sheet of paper and a crumpled one from the same height. Which lands first? Air pushes against the flat sheet.
4. Make a table: surface, distance. What does it tell you about friction?

Talk about it

• Why did the car stop?
• What would happen with no friction?

For the grown-up

Gravity pulls objects toward the Earth, and friction opposes motion. In the experiments, change only one thing at a time, the surface, to make a fair test. Newton's Principia was published in 1687.

Mark as done

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Where this comes from

• NGSS Lead States, Next Generation Science Standards: For States, By States (National Academies Press, 2013), performance expectation 3-PS2-1 (plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object)
• Isaac Newton, Philosophiae Naturalis Principia Mathematica (1687)

Written with AI assistance and checked against the sources listed. Please read it before sharing it with a child.