A truck always has more inertia than a roller skate. Does a truck always have more momentum than a roller skate? yes no
The total momentum of an isolated system of objects is conserved only if conservative forces act between the objects or regardless of the nature of the forces between the objects.
A ping-pong ball moving forward with a momentum p strikes and bounces off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum greater than p, less than p, or equal to p.
Ralph asked me a question about today's reading assignment. Suppose he is floating in outer space with no forces acting on him. He is at rest, so his momentum is zero. Now, he throws a ball. The ball goes one way, and he goes the other way. Before the collision, there was no momentum, and after the collision, there is plenty of momentum. He has momentum, and the ball has momentum. It certainly doesn't look like zero momentum, so it doesn't look like momentum was conserved. How would you answer Ralph? Momentum is a vector. Ralph and the ball go in opposite directions. The vector sum of the momentum of Ralph and the momentum of the ball is zero, the same as the initial momentum.