momentum
When skater 2 runs into skater 1, hes going faster than skater 1 so he has more momentum. Momentum is a property of a moving object that makes it hard to stop. Its a product of the objects mass and velocity. At the moment of the collision, skater 2 transfers some of his momentum to skater 1, who shoots forward when skater 2 runs into him. Whenever an action and reaction such as this occur, momentum is transferred from one object to the other. However, the combined momentum of the objects remains the same. In other words, momentum is conserved. This is the law of conservation of momentum .