Work
Definition
Energy transferred by a force pushing something through a distance. No movement, no work — no matter how hard you push.
Symbol: · Unit: joule (J)
Technical definition
The line integral of force along a displacement — W = Fd cos θ for constant force, where θ is the angle between force and displacement. By the work–energy theorem, net work equals the change in kinetic energy.
Example
Lifting a 10 kg box 2 meters straight up does about 196 J of work against gravity (W = mgh = 10 × 9.8 × 2). Carrying the same box horizontally at constant height does zero work against gravity, because the force and displacement are perpendicular.
Work in physics is not 'effort'. Holding a heavy barbell overhead is exhausting, but the physics work is zero because there is no displacement. And work is a scalar: a force perpendicular to the motion — like the normal force on a sliding block, or gravity on a satellite in circular orbit — does zero work. No motion along the force, no work.