Lever systems · GCSE PE

Parts of a lever

A lever has a fulcrum (the pivot), an effort (the force from the muscle) and a load (the weight being moved).
In the body, the joint is the fulcrum, the muscle provides the effort, and the load is the weight of the body part plus anything being held.

First class: the fulcrum is in the middle (effort, fulcrum, load). Example: extension of the neck when heading a ball.
Second class: the load is in the middle (fulcrum, load, effort). Example: plantar flexion at the ankle when standing on tiptoes or jumping.
Third class: the effort is in the middle (fulcrum, effort, load). Example: flexion at the elbow in a bicep curl, or extension of the knee when kicking.
A way to remember which is in the middle: "1, 2, 3: F, L, E" (first class fulcrum, second class load, third class effort).

Mechanical advantage = effort arm ÷ load arm. The effort arm is the distance from the fulcrum to the effort; the load arm is the distance from the fulcrum to the load.
Second class levers have a mechanical advantage: the effort arm is longer, so a large load can be moved with little effort.
Third class levers have a mechanical disadvantage: they need more effort, but they give speed and a wide range of movement, which is why most levers in the body are third class.

Fulcrum: The pivot point of a lever: the joint in the body.
Effort: The force applied to a lever, provided by a muscle.
Load: The weight or resistance moved by a lever.
Effort arm: The distance from the fulcrum to the effort.
Load arm: The distance from the fulcrum to the load.
Mechanical advantage: Moving a large load with a small effort, when the effort arm is longer than the load arm.