Force force force , in physics , a quantity that produces a change in the size or shape or the motion of a body. Energy can be used to produce a force, and the energy used in applying a force over a distance is called work .
Friction is a force that opposes motion.
The gravitational force and the electromagnetic force have an infinite range. The other two forces are short range and only act on the atomic scale. All particles experience the gravitational force, but only charged particles such as the proton, the electron and the muon experience the electromagnetic force. A 1-lb force equals 4.44822 newtons.