Lever systems
Parts of a lever
In the body, your bones act as levers. Every lever has three parts:
- the : the pivot point, which is the joint
- the : the force applied, which comes from the muscles
- the : the weight being moved, which may be the body part itself or something being lifted or thrown.
The class of a lever depends on which part is in the middle.
Key terms
The three classes
| Class | In the middle | Order | Example |
|---|---|---|---|
| First | Fulcrum | Load, fulcrum, effort | The neck |
| Second | Load | Fulcrum, load, effort | The ankle |
| Third | Effort | Fulcrum, effort, load | The elbow |
Remember
1, 2, 3: F, L, E. The part in the middle is the Fulcrum in a first-class lever, the Load in a second-class lever and the Effort in a third-class lever.
Levers in the body
- , tilting the head back to head a ball. The is the joint at the top of the spine, the is the weight of the head, and the comes from the neck muscles at the back.
- , going up onto the toes to jump for a rebound. The fulcrum is the ball of the foot, the load is the body's weight, and the effort comes from the gastrocnemius pulling up on the heel.
- , flexing in a bicep curl. The fulcrum is the elbow, the effort comes from the biceps, and the load is the weight in the hand.
Mechanical advantage
The is the distance from the fulcrum to the effort; the is the distance from the fulcrum to the load.
A lever has when its effort arm is longer than its load arm, so a small effort can move a large load.
- always have mechanical advantage, because the effort is further from the fulcrum than the load. That's why the gastrocnemius can lift the whole body onto the toes.
- have a mechanical disadvantage: the effort arm is shorter, so more effort is needed. But they give a large range of movement and at the end of the lever, which is why the arm can swing a racket or throw a ball fast.