Lesson 7 of 8

Balancing

Goal: Use moments to decide whether something balances.

Puzzles for this lesson

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Two children sitting on a level see-saw

A see-saw balances when the clockwise moment equals the anticlockwise moment.

3 m2 m1 m1 m2 m3 m300 N200 N

300 N × 2 m = 600 N m anticlockwise. 200 N × 3 m = 600 N m clockwise. The moments are equal, so it balances.

  • Two turning effects. A weight on the left of the pivot tries to turn the see-saw anticlockwise. A weight on the right tries to turn it clockwise.
  • Equal moments: it balances.
  • Unequal moments: it tips down on the side with the bigger moment.
  • Light can balance heavy. A lighter person balances a heavier one by sitting further from the pivot.

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Key words in this lesson

Moment The turning effect of a force

Pivot The point that a lever turns about

For teachers: AQA 3.1.3 Extend in part · Pearson Edexcel 42.3 · Cambridge 8Pf.04