Friction, Inertia, and other forces that affect the way things move.
There are physical forces and laws that help explain why and how things move. Watch how a wandering penny can move out from under a glass because of the forces of friction and inertia. Inertia is a force that makes objects want to keep doing what they are doing. Sir Isaac Newton came up with three laws that help us to understand how things move. We learned that friction is what makes things slow down or stop.