Work

The work done by a force is the product of the magnitude of the displacement and the rectangular component of the force in the direction of the displacement.

When a constant force P is applied to a particle, which moves a distance d in a straight line, the work done on the particle by P is defined by the scalar product

  1. When the force and displacement are in the same direction, the work done by the force is positive.

  2. When the force and displacement are in the opposite direction, the work done by the force is negative. Work of friction is always negative, since it always opposes motion.

  3. When the force and displacement are perpendicular, the work done by the force is zero.

 

In short,

U1-2 = sum of the work done on the particle between points 1 and 2

where work terms are positive/negative if they tend to increase/decrease the kinetic energy of the particle.

Units: ft-lb, in-lb, J (same as kinetic energy)