# Chapter Four: Vocabulary

## 14 terms

### NEWTON'S FIRST LAW

States that an object at rest will remain at rest, and a moving object will continue moving in a straight line with a constant speed, if and only if the net force acting on that object is zero.

### EQUILIBRIUM

The condition in which the net force on an object is zero.

### DRAG FORCE

The force exerted by a fluid on an object moving through the fluid; depends on the object's motion and properties.

### WEIGHTLESSNESS

An object's apparent weight of zero that results when there are no contact forces pushing up on the object. ( no upward acting on it)

### FREE BODY DIAGRAM

A physical model that represents the forces acting on a system.

### INTERACTION PAIR

A pair of forces that are equal in strength, but opposite in direction.

### TENSION

The specific name for a force exerted by a rope or string.

### NEWTON'S THIRD LAW

States that all forces come in pairs and that the two forces in a pair act on different objects and are equal in strength and opposite in direction.

### APPARENT WEIGHT

The force experienced by an object, resulting from all the forces acting on it, giving the object an acceleration.

### NORMAL FORCE

The perpendicular contact force exerted by a surface on another object. (something "sitting" on something else)

### TERMINAL VELOCITY

The constant velocity of an object that is reached when the drag force equals the force of gravity.

### FORCE

A push or pull exerted on an object that causes a change in motion; has both direction and magnitude and may be a contact or a field force.

### NET FORCE

The vector sum of all the forces on an object.

### INERTIA

The tendency of an object to resist change.