torque

Meaning: Torque is the rotational analog of force: how effectively a force twists an object about a pivot. Only the force component perpendicular to the pivot-to-application line produces rotation; equivalently, torque is force times the lever arm, the perpendicular distance from pivot to the line of the force. Nonzero net torque gives angular acceleration; zero net torque means rotational equilibrium.

Equation: τ = rF sinθ and τnet = Iα. τ is torque (N·m), r is pivot-to-force distance (m), F is force (N), θ is the angle between r and F, I is moment of inertia (kg·m²), α is angular acceleration (rad/s²).

On the MCAT: Usually static equilibrium: seesaw, beam on supports, or forearm holding a weight. Set clockwise torque equal to counterclockwise torque about a chosen pivot to solve for an unknown force or position; pivoting at the unknown force eliminates it. Also lever questions: a longer handle needs less force.

Common confusion: Torque and work share the unit N·m, but torque is a vector causing rotation, not an energy, so it is not given in joules. Also, a force directed along the line through the pivot gives zero torque, since sinθ = 0.