GERQUISE RILEY 5-24-11 Force in Motion Velocity The speed and direction of an object’s motion Force A push or pull that acts on an object Work Energy used when a force moves an object Power The rate at which work is done, or energy expended, per unit time. Equilibrium The state of a body or physical system that is at rest or in constant and unchanging motion. Inertia The resistance of a body to changes in its momentum. Acceleration The rate of change of the velocity of a moving body. Machine A device that applies force, changes the direction of a force, or changes the strength of a force, in order to perform a task, generally involving work done on a load.