The three classes of lever, their components (fulcrum, effort, load), examples in the body, and the idea of mechanical advantage.

What this dot point is asking

AQA wants you to identify the three classes of lever, label the fulcrum, effort and load, give examples of each in the human body, and explain mechanical advantage.

The parts of a lever

The three classes of lever

• First-class lever: effort, fulcrum, load. The fulcrum sits between the effort and the load, like a seesaw. Example: nodding the head, where the neck joint is the fulcrum.
• Second-class lever: fulcrum, load, effort. The load sits in the middle. Example: standing on tiptoes, where the ball of the foot is the fulcrum, the body weight is the load, and the calf muscles provide the effort.
• Third-class lever: fulcrum, effort, load. The effort sits in the middle. Example: a biceps curl, where the elbow is the fulcrum, the biceps provide the effort and the weight in the hand is the load.

Two further terms describe the geometry. The effort arm is the distance from the fulcrum to where the effort acts, and the load arm is the distance from the fulcrum to the load. Their relative length decides whether a lever favours force or speed, which is the key to mechanical advantage below.

Mechanical advantage

Second-class levers have a large mechanical advantage because the effort arm is long, so they can move heavy loads with relatively little effort, but slowly and over a short range. Third-class levers have a mechanical disadvantage (effort arm shorter than load arm), so they need a large effort, but they move the load a long way and quickly, which is useful for speed in sport. This trade-off matters in performance: the long, fast third-class levers at the elbow and knee let a thrower or kicker move the hand or foot a great distance very quickly, generating high speed at the end of the limb even though the muscle must work hard.