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Implications of Newton's second law for work done

Newton's second law $$F=ma$$ (where $$F$$ is the net force) implies that:

  • Work is done on an object by a particular force regardless of whether the object accelerates. The only requirement for work to be done is that the object moves in any direction (except perpendicularly) relative to the force.

  • Work is done on an object by the resultant force if the object accelerates and does not move perpendicularly to the resultant force.

A force that maintains an object at constant speed against friction does positive work. However, the net work done by the force and friction is zero (as the net force is zero).