Force in terms of newtons is expressed in the equation f=ma, that is, force (newtons) = Mass (kilograms) x Acceleration (MS-2, meters per second per second). This refers to the force needed to exert on something to increase its speed disregarding friction as a form of negative force. To work out the force applied by something when it causes impact, Forcei = mass x speed. Say a 100kg object is travelling at 10ms-1 , it is exerting a force of 1000 newtons upon impact, now if it impacts with another person of mass of 50kg, and stops completely, that other person will travel at a speed of 20ms-1 in the same direction that the original person was travelling. hope this helped.