Inertia

Inertia is like a rubber-band. Just like when you stretch a rubber-band, your hand feels like it wants to go back to where it started. Inertia is like that, but it's something that happens to objects. When something is in motion, it wants to stay in motion. And when something is at rest, it tends to stay at rest. That's because of inertia. It's a law of physics that says the only way to make something stop or start moving is to use a force.