The rack and pinion is used to convert between rotary and linear motion. The rack is the flat part with teeth, the pinion is the gear. Rack and pinion can convert from rotary to linear or from linear to rotary.
The diameter of the gear determines the speed that the rack moves as the pinion turns. Rack and pinions are often used in the steering system of cars.
Rack and pinion gears give a positive motion especially compared to the friction drive of a wheel in tarmac. In the rack and pinion railway a central rack between the two rails engages with a pinion on the engine allowing the train to be pulled up very steep slopes.
The wedge: A wedge is a simple machine used to push two objects apart. I has a triangular shape and is made up of two inclined planes. These planes meet and form a sharp edge. It can be used to separate two objects or portions of an object, lift an object, or hold an object in place
w w w . c h o m i k u j . p l / M a r W a g 9 8 7