Equal, Opposite, and Never on the Same Body

You'll learnthat interaction forces come in equal, opposite pairs acting on two different bodies.

Two skaters push off on frictionless ice. The forces match to the newton — the fates don't. Watch the pair live on two different bodies, then take the swap test everywhere it matters.

8 STEPS · 6 QUICK CHECKS · v5

FORCE LAB

Before you start

What you're looking at

Two skaters, 50 kg and 100 kg, standing palm-to-palm on frictionless ice, about to push off.

The question

During the push, who feels the bigger force, and who ends up moving faster afterward?

Watch for

Predict before it runs; watch the matched forces land on two separate bodies, yet produce different motions.

What the symbols mean

The amber arrow is the force on skater A, the blue arrow the force on skater B; each is named on-by.

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