Free-Body Diagrams and Equilibrium Rapid Review for AP Physics B & C

By — McGraw-Hill Professional
Updated on Feb 10, 2011

For a more thorough review, refer to these concepts:

Rapid Review

  • A free-body diagram is a simplified representation of an object and the forces acting on it.
  • When the net force on an object is zero, it is in equilibrium. This means that it is either at rest or that it is moving at a constant velocity.
  • To solve an equilibrium problem, draw a good free-body diagram, resolve all forces into x- and y-components, and then set the vector sum of the x-components equal to zero and the vector sum of the y-components equal to zero.
  • The units of force are newtons, where 1 N = 1 kg.m/s2.
  • Torque equals the force exerted on an object multiplied by the distance between where that force is applied and the fulcrum (the point about which an object can rotate). When an object is in equilibrium, the counterclockwise torques equal the clockwise torques.
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