Force is the external agent that, when applied to a body, brings change in the state of a body, as force can bring a moving body to rest as well as a body at rest can start moving if a force is applied to it. Mathematically, the formula for force is simply the product of the mass of a body and the acceleration produced in the body due to force, and it's written as F = ma, where m and a are the mass and acceleration of a moving body.