Put simply, a force is something which changes the momentum of an object. The magnitude of a force is the rate of change of momentum caused.

This is shown by manipulation of the famous equation ##F=ma##

##F=ma=m(v_(f)-v_i)/t=(p_(f)-p_i)/t##

Where ##F## is the force ##m## is the mass of the object ##a## is acceleration, which is the rate of change of velocity ##v_i## is the initial velocity of the object which the force acts upon ##v_f## is the object’s final velocity ##t## is time ##p## is momentum, which is equal to ##mxxv##

Extra info: Of course, because force is the rate of change of momentum, it can be linked to an object whose mass changes while velocity remains constant.

##F=(p_(f)-p_i)/t=v(m_(f)-m_i)/t##

Where ##m_f## is final mass and ##m_i## is initial mass.

Force can also be related to an object whose mass and velocity change simultaneously, but those equations involve calculus, so I won’t include those here.