* Mass: A baseball has significantly more mass than a ping pong ball. Mass is a measure of how much matter an object contains. The more massive an object, the more inertia it has.
* Inertia: Inertia is the tendency of an object to resist changes in its motion. The more massive an object is, the harder it is to get it moving or to stop it once it's in motion.
In simpler terms: Imagine trying to stop a bowling ball and a tennis ball rolling at the same speed. The bowling ball, with its greater mass, would be much harder to stop. The same principle applies to the baseball and ping pong ball.
