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In class III levers effort is situated between the load and the fulcrum. (shown in the figure below)
Lever of third order
As effort is situated between the load and the fulcrum, load arm is always greater than the effort arm. M.A. of class III lever is always < 1.
Gain in speed is obtained i.e., a larger movement of load is obtained by a smaller movement of effort.
Some of the levers are classified on the basis of the position of the forces, as shown in the figure below.
Levers classified by positions of the forces
Numerical :
The diagram shows a lever in use.
(i) To which class of lever does it belong? Give one example of this class.
(ii) Calculate its MA if AB = 2.0 m, AF = 20 cm.
(iii) Calculate the effort needed to lift the load.
Suggested answer :
(i) Class I, example: scissors
(ii) Load arm = AF = 20 cm.
Effort arm = BF = AB - AF
= 200 - 20
= 180 cm
