Ans. With levers of class III, we do not get gain in force, but we get gain in speed, that is a longer displacement of load is obtained by a smaller displacement of effort.
Q.32. Draw a labelled sketch of a class III lever. Give one example of this kind of lever.
One example of this kind of lever is foot treadle.
(a) A bottle opener is a lever of the second order, as the load is in the middle, fulcrum at one end and effort at the other.
(b) Sugar tongs is a lever of the third order as the effort is in the middle, load at one end and fulcrum at the other end.
a. A Seesaw
b. A Common balance
c. A nut cracker
Ans. (a) Class III.
Here, the fulcrum is the elbow of the human arm. Biceps exert the effort in the middle and load on the palm is at the other end.
(b) Class II.
Here, the fulcrum is at toes at one end, the load (i.e. weight of the body) is in the middle and effort by muscles is at the other end.
It is Class III lever.
Class I lever in the action of nodding of the head: In this action, the spine acts as the fulcrum, load is at its front part, while effort is at its rear part.
Class II lever in raising the weight of the body on toes: The fulcrum is at toes at one end, the load is in the middle and effort by muscles is at the other end.
Class III lever in raising a load by forearm: The elbow joint acts as fulcrum at one end, biceps exerts the effort in the middle and a load on the palm is at the other end.