Fig 9Moments and equilibriumΣF = 0 and ΣM = 0torque = F × d
A force's turning effect about a point is its moment (or torque): force × the perpendicular distance from the point to the force's line. For anything at rest, the forces add to zero and the moments about any point add to zero. On the see-saw, 60 kg at 1.5 m balances 78 kg at 1.15 m. On the beam, take moments about one support to find the other support's force in one step, then use ΣF = 0 for the first.