Moments And Levers P

Try to shut a heavy door by pressing on it a centimetre from the hinges. You will push until your arm aches and the door will barely shift. Move your hand out to the handle, use a fraction of that effort, and the door swings closed. Nothing about the door has changed and nothing about your strength has changed. What changed is the distance, and distance is the second half of every turning problem in physics.

This lesson gives you the quantity that measures a turn: the moment of a force, worth force multiplied by perpendicular distance, measured in newton metres. You will use it to balance a beam by setting the clockwise turns against the anticlockwise ones, to work out an unknown force or an unknown distance from that balance, to predict the exact moment a crate or a bus stops leaning and starts falling, and to explain how a crowbar lets a pair of hands move a boulder that no pair of hands could ever lift.