What is levers and types of levers ?

A lever is a  unchangeable bar which is  efficient of movement about a fixed point called a (F)  fulcrum . Work is done when a force or  (E) effort, applied at one point on the lever, acts upon another force or weight (W), acting at second point on the lever. The perpendicular distance from the fulcrum to the effort (E) may be called the effort arm and that from the fulcrum to the weight (W) as the weights arm.

 Lever is represented by a bone, which is efficient of movement about a fulcrum formed at the articulating surfaces of a joint; 

⏩the effort which works the lever is supplied by the force of mus cular contraction, applied at the point of insertion to the bone.

⏩while the weight may be either at the centre of gravity of the part moved, or of the object to be lifted.

There are three Orders / types or Classes of levers, each of which is characterised by the relative positions of the fulcrum, effort and weight.

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Mechanical Advantage.
Examples of all three Orders of levers 

Lever at Home and at Work 

Three types of levers↓↓↓

Ist Order⇛

The fulcrum is situated centrally the effort and the weight; 

it may be situated centrally, or towards either the effort or the weight, consequently the effort's and the weight's arms may be equal, or one may exceed the other in length.

 

Fulcrum is situated centrally the effort and the weight

2nd Order.⇛

 The weight is between the fulcrum and the effort, and the effort arm must therefore always exceed the weights arm.

3rd Order⇛. The effort is between the fulcrum and the weight, and the weights arm must therefore exceed the effort arm.

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Mechanical Advantage.

Examples of all three Orders of levers 

Lever at Home and at Work