| additive vector quantity characterizing external interactions on a particle or body|
NOTE 1 Forces cause the particle or body to change its momentum p = mv according to the second Newton law: dp/dt = F (in inertial frame), where F is the resultant of all acting forces. The equation applies also in the theory of relativity.
NOTE 2 Force may lead to the deformation of the body.
NOTE 3 In any inertial frame, a resultant force F acting on a body with constant mass m causes an acceleration a = F/m of the centre of mass of the body.
NOTE 4 The coherent SI unit of force is newton, N.