# Chapter 19: Motion

## 10 terms

### force

A push or a pull.

### Net force

The combination of all forces acting on an object.

### Balanced forces

Two or more forces whose effects cancel each other out and do not change the motion of an object.

### Unbalanced forces

Two or more forces acting on an object that do not cancel, and cause the object to accelerate.

### Newton's first law of motion

If the net force acting on an object is zero, the object will remain at rest or move in a straight line with a constant speed.

### friction

Force that acts to oppose sliding between two surfaces that are touching.

### Newton's second law of motion

An object acted upon by a net force will accelerate in the direction of the force, and the acceleration equals the net force divided by the object's mass.

### Weight

Gravitational force between an object and Earth.

### Center of mass

Point in an object that moves as if all of the object's mass were concentrated at that point.

### Newton's third law of motion

Forces always act in equal but opposite pairs.