momentum
The universe has many remarkable qualities, among them a rather beautiful symmetry: the total amount of motion in the universe balances out always. This law only makes sense if we measure motion in a specific way: as the product of mass and velocity. This product, called momentum , can be exchanged from one object to another in a collision. The rapidity with which momentum is exchanged over time is determined by the forces involved in the collision. Conservation of momentum is one of the five fundamental conservation laws in the universe. The other four are conservation of energy, angular momentum, charge conservation and CPT conservation.