Action & Reaction

Forces come in pairs

An interactive lesson with 8 steps, about 7 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Forces come in pairs: A on B and B on A, with the same size and opposite directions.
• The two forces in a pair act on different objects, so they never cancel each other.
• To predict an object’s motion, add up only the forces acting on that object.

Steps

1. Splat
2. Newton’s third law
3. Find the partner
4. The horse and cart
5. Rockets in space
6. Skaters
7. Push apart
8. A tempting pair