Compound Machine:   Two or more simple machines working together to make work easier.
Examples: Wheelbarrow, Can Opener, Bicycle

Distance A machine can make work easier in three ways: Any change in the size of the force changes the distance (see force). No machine can increase both force and distance.
 

Force : You are doing work when you use a force to cause motion. Machines make work easier, but they need energy to do work. A person is usually the source of energy for a simple machine. A person uses a force to operate a simple machine. A force is a push or pull. The force applied to to the machine is called work input or effort force.

 

Gears: A gear sometimes is viewed as a simple machine, but it is really just a wheel with teeth. Two toothed wheels fit together either directly or through a chain or belt so one wheel will turn the other. Some gears may have a screw or a toothed shaft in place of one of the wheels. A gear may also be a combination of toothed wheels that produces a certain speed (such as a bicycle's top gear which makes the bike go fast, and the low gear for slow speed.)
Examples: Clock, Automobile, Drill

Inclined plane: A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed.
Examples: Staircase, Ramp, Bottom of a Bath Tub
 

Lever: A straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending on the weight of the object to be lifted or the force you wish to exert. Pushing down on one end of a lever results in the upward motion of the opposite end of the fulcrum.
Examples: Door on Hinges, Seesaw, Hammer, Bottle Opener

Pulley: A wheel that usually has a groove around the outside edge. This groove is for a rope or belt to move around the pulley. Pulling down on the rope can lift an object attached to the rope. Work is made easier because pulling down on the rope is made easier due to gravity.
Examples: Flag Pole, Crane, Mini-Blinds

Screw: An inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated.
Examples: Bolt, Spiral Staircase

Simple Machine: Simple machines are "simple" because most have only one moving part. Some are so simple, they don't have any moving parts! Simple machines make work easier.
Examples: Screw, Wheel and Axle, Wedge, Pulley, Inclined Plane, Lever

Wedge: Two inclined planes joined back to back. Wedges are used to split things.
Examples: Axe, Zipper, Knife

Wheel and Axle: A wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a greater distance than the axle, but less force is needed to move it. The axle moves a shorter distance, but it takes greater force to move it.
Examples: Door Knob, Wagon, Toy Car

Work: You are doing work when you use a force to cause motion. To measure the amount of work you do, multiply the force times the distance the object moved.