Moments on a beam

Drag weights along a beam to balance it on a pivot and compare the clockwise and anticlockwise moments, or support the beam at both ends and see how the two reaction forces share the load.

Set-up

Pivot position

Beam weight (uniform)

Weight A

Weight

Position from left end

Weight B

Weight

Position from left end

Weight C

Weight

Position from left end

Try this

With the pivot at 0.50 m and A = 4 N at 0.20 m, predict where the 2 N weight B must go to balance the beam, then drag it there to check.
Set A and B to 0 N, the beam weight to 6 N and move the pivot to 0.30 m. Where must a 6 N weight C go to stop the beam tipping?
Switch to supported at both ends with a single 8 N load. Drag it from one end to the other: where are R₁ and R₂ equal, and what is R₁ + R₂ always?

Common error: measuring the distance from the end of the beam instead of the perpendicular distance from the pivot (or from the point you take moments about) gives the wrong moment every time.

Practise this topicQuestions: section 1 IGCSE Physics notes Test builder Diagnostic test

More on 1: Distance–time and velocity–time graphs · Stopping distance · Hooke's law and the limit of proportionality · Skydiver and terminal velocity · Momentum in collisions

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