The Cauchy momentum equation is a mathematical equation used to tell us how things move. It helps to explain how a force can cause an object to move.
The equation says that the rate of change of momentum of an object (that's how fast it is moving) is equal to the force that's applied to the object divided by the mass of the object.
In other words, if you push an object it will move. The amount that it moves depends on how much force you apply, the mass of the object and the time it takes for you to apply that force. This equation helps us to understand how this works.