# Chapter 9 Motion & Chapter 10(I) Force & Gravity

## 20 terms

### Motion

when an object's distance from another one is changing

### Velocity

speed in a given direction

### Acceleration

rate at which speed or velocity changes. Speeding up, slowing down, changing direction

### Reference Point

a place/object used for comparison to determine if something is in motion

### Constant Speed

when the speed of an object does not change

a push or a pull

### Weight

the force of gravity acting on an object or person

### Mass

total amount of matter that make up an object or person

### Friction

force that one surface exerts on another when they rub against each other

### Rolling Friction

when one surface rolls over another

### Fluid Friction

when an object moves through liquid or gas

### Free Fall

when gravity is the only force acting on an object

### Air Resistance

a type of friction where air acts against gravity

### Law of Universal Gravitation

when two objects in the universe attract each other

### Gravity

the force that pulls falling objects toward Earth

distance / time

### Acceleration

final speed - initial speed / time

### Average Speed

total distance / total time

### m/s2

example of a unit of acceleration

### m/s

example of a unit of speed