Quick Recap — Forces, Equilibrium & Weight
- Free-body diagram: mark every force on the body — weight, normal, tension, friction, applied force.
- Equilibrium: the net force is zero; three concurrent forces obey the triangle law.
- Weight ; on a horizontal surface the normal force equals the weight when there is no vertical acceleration.
- Apparent weight in a lift: moving up, moving down, and in free fall.
- Circular motion: a net centripetal force points to the centre; on a level road friction supplies it, and its work is zero.