Pulley

Reasons to use a pulley:

• Change the direction of an applied force 
• Transmit rotational motion 
• Realize a mechanical advantage in either a linear or rotational system of motion

Pulleys are composed of a wheel on an axle or shaft
that may have a groove between two flanges along the edge

A rope, cable, belt, or chain usually runs over the wheel and inside the groove
if present.

Belt and pulley systems transmit mechanical power, torque, and speed across axes, and if the pulleys are of differing diameters, realize a mechanical advantage.

Rope and pulley systems transmit a linear motive force (in tension) to a load through one or more pulleys for the purpose of pulling the load.

A fixed pulley has a fixed axle
and is used to change the direction of the force on a rope
and has an MA = 1

A movable pulley has a free axle
and is used to multiply forces
and has an MA = 2

A block and tackle system uses a combination of fixed and movable
and has an MA > 2