An object in motion stays in motion, and an object at rest stays at rest unless a force acts on it (also called the Law of Inertia)

An object's resistance to changing its motion (e.g., your body lurching when a car stops suddenly)

A push or pull that changes an object's motion (e.g., kicking a ball, gravity pulling things down)

Equal forces acting in opposite directions, causing no motion change (e.g., a book sitting still on a table)

Unequal forces that change an object's motion (e.g., a soccer ball speeding up when kicked)

A force that slows things down by rubbing against surfaces (e.g., bike brakes, shoes on pavement)

The force that pulls objects toward each other (e.g., Earth pulling you down!)

The amount of "stuff" in an object (more mass = more inertia)

Speed in a specific direction (e.g., a car going 60 mph north)

Any change in speed or direction (e.g., a car speeding up, slowing down, or turning)

When an object isn’t moving (e.g., a pencil on your desk)

How hard it is to stop a moving object (mass × velocity)

Friction from air pushing against moving objects (e.g., parachutes slowing skydivers)

A substance that reduces friction (e.g., oil in bike chains, wax on skis)

Friction when objects roll (e.g., wheels on pavement—less than sliding friction!)

Friction that keeps stationary objects from sliding (e.g., your feet gripping the floor)

Friction when objects slide past each other (e.g., a sled on snow)

The total force acting on an object (combines all pushes/pulls)

The unit to measure force (named after Sir Isaac Newton!)