# 4th grade Unit 4 Science - Forces and Motion

## 21 terms

### simple machine

one of the basic machines that make up other machines

### lever

a simple machine made up of a bar that turns on a fixed point

### fulcrum

the fixed point, or point that does not move, on a lever

### effort force

the force put on one part of a simple machine, for example, when you push or pull on a lever

### work

that which is done on an object when a force moves moves an object through a distance

### pulley

a simple machine made up of a rope or chain and a wheel around which the rope or chain fits

### wheel and axle

a simple machine made up of a large wheel attached to a smaller wheel or rod

### inclined plane

a flat surface with one end higher than the other

### efficiency

how well a machine changes effort into useful work

### screw

an inclined plane wrapped around a pole

### wedge

a machine made of two inclined planes placed back-to-back

a certain place

### motion

a change of position

### frame of reference

the things around you that you can sense and use to describe motion

### speed

a measure of an object's change in position during a unit of time; for example, 10 meters per second

a push or pull

### newton

the metric, or System International(SI) unit of force

### acceleration

a change in the speed or direction of an object's motion

### gravity

a force that pulls all objects towards each other

### weight

a measure of the force of gravity upon an object

### friction

a force that keeps objects that are touching each other from sliding past each other easily