In the most general sense, force denotes the faculty of action or the power to overcome a resistance. In the physical sciences it is that entity that changes, or tends to change, the state of rest or of motion of a body. Consequently, it may also be defined as the cause of motion, or more precisely—assuming the validity of the principle of inertia, according to which unaccelerated motion and rest are dynamically and causally equivalent and correspond merely to different choices of the reference systems—as the cause of acceleration.

The metric unit of force in science is the dyne, which is the force necessary in order to give a mass of one gram an acceleration (increase of velocity) of one centimeter per second in each second. The British unit of force is the poundal, which is the force necessary to give a mass of one pound...