1. simple machine
A simple device or invention for altering the magnitude or direction of a force.
The six basic types are the lever, wheel and axle, pulley, screw, wedge, and inclined plane.

2. effort force
To determine the mechanical efficiency of a machine, you need to determine the output force and the effort force, or the force you exert on the machine to cause it to do its work. 

3. resistance force
resistance force is the force which an effort force must overcome in order to do work on an object via a simple machine.

4. pulley
A machine consisting of a wheel over which a pulled rope or chain runs to change the
direction of the pull used for lifting a load.

5. single pulley system
A pulley is a grooved wheel intended for use with a rope, cable or other flexible fiber. The rope is placed around one side of the pulley to change the direction of the force applied.

6. double pulley system
System consisting of two pulleys with a rope running around them to lift a load. Using two or more pulleys reduces the amount of effort needed.

7. What is a pulley?
A pulley is a simple machine with a wheel over which a belt, cable, chain, or rope runs. Pulleys are used to lift and pull things. A simple pulley is connected to a load at one end and a person or other device at the other end to pull the rope or chain. The rope runs over the wheel, allowing the load to be lifted or moved.

8. How do elevators work?
A cable elevator actually uses a simple machine called a pulley to lift the elevator box up and down. A pulley is a simple machine with a wheel, over which runs a belt, cable, chain, or rope. In an elevator, the box that people ride in is encased in a tall elevator shaft. The top of the box is connected to steel ropes that are connected to a pulley, controlled by a motor.