Why does one need to exert different amount of force when using the three classes of levers?When using first, second and third class lever, the force may be greater or smaller than the load. Why is...

Why does one need to exert different amount of force when using the three classes of levers?

When using first, second and third class lever, the force may be greater or smaller than the load. Why is this so?

Asked on by limjiahui

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neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

A lever is a device where you apply a force to make an object move about a fulcrum.The levers are of 3 types , according as the postion of application of force, position of the fulcrum and the postion of the load.The  first class of lever has the fulcrum in the middle and the applicaton of the force and the load are on the opposite sides of the fulcrum. Scissors, pliers and  a See-saew are the examples. If you increase the distance of effort or application of foce, you can gain a  mechanical advantage of using less force to move the load.

In the second class of lever the load is in the middle and the fulcrum and efforts are on opposite side.A nut craker is the example . There is no mehanical adventage in the efforts. Both force and the load move in the same direction. The closer the efffort to the load, more the effort.The force could be less if the load is closer to fulcrum and the effort is  more distant from the load.

The third  class of Lever uses the effort or  force in the middle and the fulcrum and the load are at either side. A fishing rod, a pair of tongs are the examples. The mechanical adventage is more if effort closer to the load  and more effort or force is required if the application of force is shifted towards the fulcrum.

krishna-agrawala's profile pic

krishna-agrawala | College Teacher | (Level 3) Valedictorian

Posted on

Lever is a simple machine which consists of a lever or a rod which swings around a fixed pivot called fulcrum. This mechanism provides a mechanical advantage in moving a load with effort that is less than the load. Lever makes it possible by changing the ratio of movement of the load and the effort. When an effort is applied directly to a load the length of movement of load and the effort is exactly same. But by using a lever it is possible to change this ratio. When the lever swings around its pivot the distance moved by different points on the lever is directly proportional to their distance from the fulcrum. The points nearer to the fulcrum move less and those away from the fulcrum move more. Points just on the fulcrum do not move at all. Therefore by changing the points on lever where load is placed and effort is applied and the position of the fulcrum it is possible to achieve different degrees of mechanical advantage. The exact relationship between the load and effort is give by the equation below.

Load x Distance of load from fulcrum = effort x Distance of effort from fulcrum.

Thus if distance of load from fulcrum is twice the distance of effort from fulcrum the effort required to move the load will be half the load. This amounts to mechanical advantage of 2.

The levers are classified in three classes depending on the relative positions of the fulcrum, load and the effort.

In first class of levers the fulcrum is in the center and the load and efforts are on opposite sides of the fulcrum. In this type of lever it is possible to have distance of load from fulcrum either more than or less than the distance of effort from the fulcrum. Thus the effort can be less or more than the load. Examples of first type of levers are see-saw and scissors.

In second class of lever the fulcrum is at one end to the lever and the effort at the other end. The load is always between the fulcrum and the effort. In this type of levers the distance of load from fulcrum is always less than the distance of force. Therefore the force is always less than load. Examples of this type of lever are nutcracker and bottle opener.

In third class of lever  fulcrum load are on two extreme end of the lever, and the effort is between them. In this type of levers the distance of load from fulcrum is always more than the distance of force. Therefore the force is always more than load. Examples of this type of lever are tongs and tweezers.

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