What Does Conservation of Motion Mean?

Rene Descartes, a French physicist during the 1600s, came up with the idea of conservation of motion that stated the total "quantity" of motion in a system is conserved. For example, if a moving object hit a wall and changed direction, there would be no change to its quantity of motion.

Facts

This theory attempted to predict the behavior of objects in a system with no outside forces. Descartes explicitly defined motion as simply the product of size and weight. His theory did not include mass and stated that speed, not velocity, was the property being conserved.

Considerations

The main problem with conservation of motion is that not all variables are accounted for. Descartes had almost, in essence, stated the modern law for conservation of momentum, but he failed to consider the implications of mass and velocity in his formulation.

Significance

This notion that conservation of a few distinct properties does occur in the universe helped lay the foundation for the three main laws of conservation that are accepted today. This eventually revolutionized the fields of kinematics and classical mechanics, which are two branches of physics that deal with describing the behavior of objects.

Resources

• Stanford Encyclopedia of Philosophy: Descartes' Physics