Simple Machines

Simple machines are devices which reduce the amount of force needed to do a task by lengthening the distance of movement.
Two types of action are involved in the use of simple machines: mechanical work, and torque.
Mechanical work is defined as force times distance, when the two are in the same direction. Torque is defined as force times distance when the two are at right angles to each other. Distance for torque application, also known as leverage, is measured from a pivot point called the fulcrum.
In doing a task with a simple machine, the work or torque you put in is always equal to the work or torque that the machine puts out; you don't "save" any energy when using a simple machine.
Expending energy is easier on you if you do it gradually; simple machines let you do a given task gradually so that less force is required.

Input work or torque = Output work or torque

F x d = F x d

Work examples

Inclined plane: you push with a small force to lift something, because you are only pushing against a part of an object's weight; the tradeoff is that to lift it high you have to move far.
Block-and-tackle pulley system: a set of wheels on a common axle hangs from the ceiling, and another set of wheels on a common axle is attached to a heavy object near the floor. A long length of rope is strung up and down between pairs of the lower and upper wheels, ending in a section that hangs down on which you pull. As you pull with a small force to draw a long length of rope from the wheels, the many rope sections between the wheel sets pull collectively with large force on the object to lift; the tradeoff is that to lift it high you have to pull out a very long length of rope.

Levers: a horizontal bar is attached to a hinge or fulcrum at one end or somewhere along its length. A heavy object or large opposing force pushes down near the hinge, which you are able to lift with a small force applied far from the hinge. Classic examples: crowbar, wheelbarrow.
Wheel and axle: a large diameter wheel is rigidly attached to a small diameter wheel or axle. The axle may have gear teeth on it, or be wrapped by a rope or drive belt, such that when it is turned it must apply a large force on something hard to move. By applying a small force to the rim of the large wheel, you can easily turn the axle and the attached equipment; the tradeoff is that to move the item a short distance you may have to rotate the large wheel many times around. Classic examples: automobile steering wheel, doorknob, screwdriver.