Paper 1 · Module
Forces, density and pressure
Moments, couples and equilibrium
The moment of a force is force times the perpendicular distance from the pivot to its line of action. A couple is a pair of equal, opposite, parallel forces: it turns without moving the object along, with torque one force the separation. An object is in equilibrium when the resultant force and the resultant moment are both zero; then its forces form a closed vector polygon.
≈ 40 minDensity, pressure and upthrust
Pressure in a fluid increases with depth: . Because the pressure on the bottom of a submerged object is greater than on its top, there's a net upward force, the upthrust, equal to the weight of fluid displaced: . An object floats when the upthrust equals its weight.
≈ 35 min