Mechanical Advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. This is calculated as the ratio between the input force, and the output force of the device/tool.
For example, "Some Device" that is able to turn a 10 N input force into a 20 N output force is said to have a mechanical advantage of 2.
NOTE: Because mechanical advantage is a ratio, it does not have a unit.
Simple Machines
Typically, we will achieve mechanical advantage by employing simple machines. A simple machine is a mechanical device that changes the direction and/or magnitude of a force and come in a few varieties.
Inclined Plane
An inclined plane, also known as a ramp, is a flat supporting surface tilted at an angle from the vertical direction, with one end higher than the other, used as an aid for raising or lowering a load.
Examples: Ramps, slides, roofs
Levers
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. Levers are then classified by the relative positions of the fulcrum, input, and output forces.
Examples: See-saws (first-class), wheelbarrows (second-class), fishing rod (third-class)
Wedge
A wedge is a triangular shaped tool that is typically used to separate two objects or portions of an object. It can also be used to hold objects in place, and resembles a portable inclined plane.
Examples: Axes, door-stoppers, knives
Wheel & Axle
The wheel and axle is a simple machine, consisting of a wheel attached to a smaller axle so that these two parts rotate together, in which a force is transferred from one to the other. The wheel and axle can be viewed as a version of the lever, with a drive force applied tangentially to the perimeter of the wheel, and a load force applied to the axle supported in a bearing, which serves as a fulcrum.
Screw
The screw is a simple machine that converts rotational motion to linear motion, and a torque (rotational force) to a linear force. The amount of mechanical advantage achieved by a screw depends on both the input radius, and the pitch length.
The input radius is considered to be the distance from where the force is applied, to the axis around which the screw spins. The pitch length is the distance between each threads of the screw, or how long the screw has moved after one rotation.
Other Types of Machines
Up until this point, we have discussed simple machines which are well... simple. They are comprised of very few parts -- sometimes only one.