Motion Doesn’t Need a Motor

You'll learnthat an object with zero net force keeps its velocity, so motion needs no push.

A puck coasting on frictionless ice, a crate dragged at constant velocity, a projectile whose force ignores its velocity entirely — and the 400-year-old instinct that something must be pushing.

8 STEPS · 6 QUICK CHECKS · v3

FIRST LAW LAB

Before you start

What you're looking at

A puck sliding across frictionless ice at a steady 3 m/s, its free-body diagram riding along, the stick long gone.

The question

With nothing pushing it, what keeps the puck going?

Watch for

The dashed 'leftover push' arrow — the instinct that a used-up force still sits inside the puck.

What the symbols mean

Solid arrow = velocity (3 m/s); dashed grey arrow = the imagined leftover push; the FBD shows weight down, normal up.

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