Great Idea 5

Idea5: Conservation of momentum

        The idea of momentum, was developed by the French scientist and philosopher René Descartes, before Newton. By “momentum”, he meant “amount of motion”.  Descartes also tried to introduce the  general principle of conservation of momentum in collisions.  He believed that the total “quantity of motion” in the universe is conserved.  But the first correct statement of conservation of momentum was given by English mathematician John Wallis, in 1670, in his Mechanica sive De Motu, Tractatus Geometricus.

     However, it turns out that conservation of momentum can be deduced from Newton’s laws, as outlined in Newton’s Philosophiæ Naturalis Principia Mathematica(1687). In the absense of external forces the total momentum of a system remains unchanged. The momentum of an object is that object’s mass multiplied by its velocity. The law of conservation of momentum states that the total momentum of all the objects in the universe never changes.

 The law of conservation of momentum helps us understand collisions between objects. The total momentum before a collision equals the total momentum after a collision. We can use this fact to understand how the velocities of objects before a collision relate to velocities after a collision.