Levers are the simple machines through which work coud be done easily.The functions of the levers involve to work with (i) heavy loads with little force, (ii) to increase magnitude of the force ,(iii) to increase the rate of work and (iv) change the direction of force.
There is mechanical advantage and the the eficiency of the levers . The mechanical advantage is the ratio of the Load to the effort, or
M.A= Load/Effort=distance of the load from fulcrum/distance of the effort from the fulcrum
The efficiency of the lever is work done by the load/work done by the effort = Load (force)*distance travelled by the load/(Effort(force)* distance acted by effort)
The efficiency of the machine (lever) is 100% if all the input energy applied is converted into output energy without any loss of energy due to friction or air resistance etc.
The mechanical advantage could be improved by suitably increasing the load fulcrum distance over the fulctum effort distance.
Levers are grouped in three classes depending on the position of fulcrum, effort and load or resistance. Class 1 lever have fulcrum located between the effort and load. Class 2 levers have fulcrum at one end, and effort at the other end, the load being located between the two. In class 3 lever fulcrum is located at one end, and load at the other end, the effort being located between the two.
In levers the multiple of magnitude of a load and its distance from the fulcrum is equal to multiple of magnitude of a effort and its distance from the fulcrum. Thus if the fulcrum is located at point O, load L at point A, and effort E at point B, Then
L x OA = E x OB
In class 1 levers, the distance of load from fulcrum can be less than, equal to, or more than the distance of effort from fulcrum. Accordingly, effort can be respectively less than, equal to, or more than the load. Thus class 1 lever make it easier or difficult to move things, depending on weather their distance from fulcrum is less or more than that of effort.
In class 2 levers the distance of load from fulcrum is always less than that of effort. As a result effort is always less than load. Thus class 2 levers always make it easier to to move things.
However, type of lever do not effect efficiency. Efficiency is defines as amount of work output in form of movement of load divided by amount of work done in form of movement of effort. Theoretically these two are always same irrespective of class of lever or the ratio of load and effort. Therefore theoretical efficiency of levers of all types is always zero.