# Mechanisms Revision Cards

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## What are mechanisms?

Mechanisms are a system of parts working together. they are usually devices that use forces and movements. mechanisms usually cosist of moving parts such as:

• Gears
• Belt and Chains
• Followers
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## Levers and Linkages

Levers can be used in addtion to human muscles; they help humans to do jobs which could not be done otherwise because of their limited strength.

One of the oldest mechanisms is the lever. Stone age people used them to move large objects.

A lever makes life easier! - Moving things, Lifting things.

An example of a leaver is a jaw.

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## Levers and Linkages Continued

Levers are an essential part of many mechanisms. they can be used to change the ammount, the strength and the direction of movement.

Like a see-saw or ballance, the loadand the force work together. As one moves up the other moves down.

Linkages are lots of levers joined together. The piviot is an essential part of the lever system.

Linkages are an essential part of many mechanisms. They can be used to change direction, alter speed and change the timing of moving parts.

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## Cranks

The crank is used to convert or change rotary motion to reciprocating or oscillating motion.

With careful timing it can also be used to convert motion the other way; from recipricating to rotary.

Rotary= movement in a circular motion.

Reciprocating= moement backwards and forwards or up and down.

Oscillating= movemnt from side to side in a half circle motion e.g. a grandfather clock pendulum.

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## Gears

Gears are used to change speed in rotational movement.

A gear is different form, a pulley in that a gear is a round wheel which has linkages.

Gears turn in alternate directions.

Gears turning in the same direction would not be able to turn as the gears would lock together.

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## Pulleys

A pully is a wheel on an axle that is designed to support movement of a cable or belt along its circumferance.

Simple Pulley- as the rope is bulled down the weight moves up by the same distance.

Compound Pulley- the rope is wrapped around two pulleys. As the rope is pulled the weignt, this time attatched to the lower pully rather than direct to the rope, moves up slower than the speed that the rope is pulled.

By wrapping the rope several times around the pulleys it is easily possible to lift your own weight off the ground.

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## Rack and Pinion

Rack and Pinion can convert from rotary to linear or from linear to rotary.

A pinion is a gear; a rack is a flat toothed part.

The rack and pinnion reduces the force needed to move objects and most importantly protects the machine operator from his/ her back from excessive strain.

Rack and pinions are commonly used in the stearing system of cars to convert the rotary motion of the steering wheel to the linear motion (side to side) of the car wheels.

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## Chain and Sprocket

Chains are used to connect gears. They work in a similar way to pulleys but with a positive drive rather than a reliance of friction.

Gears which are connected by chains turn in the same direction unlike gears which mesh against each other.

Like gears, chains and sprocket drives are used to transmit rotary motion from one place to another.

Unlike gears however, the direction of rotation for wheels within the chain is the same.

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