# Chapter 10: Forces

## 20 terms

### force

a push or pull on an object

### newton

the strength of a force measured in the SI system

### net force

the combination of all of the forces acting on an object

### unbalanced forces

result in a net force that causes a change in a object's motion

### balanced forces

equal forces acting in opposite directions

### friction

the force that two surfaces exert on each other when they rub against each other; acts opposite the direction of motion

### static friction

the friction that acts on objects that are not moving; acts opposite the direction of motion

### sliding friction

occurs when two solid objects slide over each other; acts opposite the direction of motion

### rolling friction

occurs when an object rolls over a surface; acts opposite the direction of motion

### fluid friction

occurs when a solid object moves through a liquid; acts opposite the direction of motion

### gravity

a force that pulls objects towards each other

### weight

force of gravity acting on the a person or object at the surface of the planet

### free fall

occurs when the only force acting on an object is the force of gravity

### mass

a measure of the amount of matter in an object

### air resistance

an upward force exerted on all falling objects

### terminal velocity

the greatest velocity a falling object reaches

### projectile

an object that is thrown

### inertia

tendency of an object to resist a change in motion

### momentum

characteristic a moving object that is related to the mass and velocity of the moving object

### law of conservation of momentum

the total momentum of objects that interact does not change