MEPX
Chapter 5 of 10All chapters
  1. 1Describing motion
  2. 2The laws of motion
  3. 3Free body diagrams
  4. 4Friction and normal forces
  5. 5Equilibrium and torque
  6. 6Work and energy
  7. 7Momentum and collisions
  8. 8Circular motion
  9. 9Projectiles
  10. 10Solving problems

Chapter 5 of 10

Equilibrium and torque

Nothing moving, nothing turning.

Two conditions

For an object at rest, forces must cancel and turning effects must cancel. Torque is force times perpendicular distance from a chosen pivot.

  • Choosing the pivot at an unknown force removes it from the equation.
  • A ladder against a wall is the classic problem needing both conditions.

Centre of mass

An object topples when its centre of mass passes outside its base. That single idea explains stability of vehicles, furniture and people carrying loads.