Answer
A lever may be defined as a rigid bar, or as a mechanical device for doing work . In anatomical considerations the bones in the body act as levers -- joints are the fulcrum ;the power or effort is supplied by muscles; the resistance ( weight or load) is the body part to be moved (+ any weight attached to it or being held by it). Therefore, the three components of a lever system are fulcrum (F), effort or power (E), and resistance or weight/load (R).
E for effort (power)
F for fulcrum
R for resistance (weight/load)
Work Step by Step
There are three orders or classes of levers. The classification depends on the positions of the three factors, effort, fulcrum, and resistance:
First class : R F E---fulcrum in the middle
Second class: E R F --- resistance in the middle
Third class : R E F ---effort in the middle
