Moment Master
Balance a metre rule, push a trolley and investigate stability. Use g = 10 N/kg.
Metre rule
Within the limit of proportionality, Hooke's law describes the stretch of a spring: F = kx.
Clockwise and anticlockwise moments
Challenge
Move the controls and press Check.
The physics
Weight: W = mg. Horizontal resultant: Fnet = ma. Static friction balances a small push, up to its limiting value. Sliding friction is assumed equal to limiting friction.
Moment: M = Fd sin θ in N m. A rigid beam balances when clockwise and anticlockwise moments about the pivot are equal. Include the beam's weight acting at its centre of gravity.
Stability: a block topples when the vertical line of action of its weight passes outside the supporting base. A lower centre of gravity gives a larger critical tilt for the same base width.