One Number That Refuses to Change

You'll learnthat with no external force, a system’s total momentum stays fixed through any event.

A rear-end, a head-on, an explosion, and a cannon shot. Four different dramas, one boundary, one signed sum — and a ledger that reads exactly the same before and after every one of them.

8 STEPS · 6 QUICK CHECKS · v5

MOMENTUM LAB

Before you start

What you're looking at

A frictionless track with a 3 kg cart at +4 m/s bearing down on a parked 1 kg cart, beside a signed momentum ledger.

The question

Through a collision, an explosion, and a cannon shot, will the outlined total bar ever move?

Watch for

The individual bars shifting during each event; predict whether the outlined total holds steady across them all.

What the symbols mean

Each pink bar is one object’s signed momentum (kg·m/s); the outlined TOTAL bar is the whole system’s momentum.

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