Forces and Motion | Energy and Thermal Physics

Predicting momentum

Classroom Activity for 14-16 Supporting Physics Teaching

What the Activity is for

This is a quick puzzle, best done as a physical presentation, to compare the momentum of two very dissimilar balls after they have been subjected to the same impulse.

If both start at rest then of course they'll have the same momentum as a result of action of the same impulse, whatever the comparative masses, and so velocities.

What to Prepare

  • a pair of balls of very different sizes
  • a straw
  • a smooth channel, to constrain the balls to the same line of motion
  • access to this software assembly kit for constrained quantities, QWC (see below)

What Happens During this Activity

Put both balls side by side in their tracks. Blow on both so as to exert the same force for the same time.

Teacher: I exerted the same force for the same time, on both. What can you tell me about the impulse on each ball?

Teacher: Which has the greater momentum?

You might also use the downloaded interactive to build a model of the trade-off between velocity and mass that you've shown physically.

You might also show one or more of the interactives from the Physics Narrative to complement the physical contrast you've shown.


Download the interactive for this activity.

appears in the relation p=mv F=dp/dt λ=h/p ΔxΔp>ℏ/2
has the special case Angular Momentum
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