Lever Classes and Mechanical Advantage

Levers in the body

A lever is a rigid bar that turns around a fixed point. In the body the bones are the bars, a joint is the fixed point, and a muscle provides the force. Every time you move, you are using a lever. In this module you learn the three classes of lever, how to tell them apart, and how to work out the mechanical advantage a lever gives.

Fulcrum, load, effort

Four terms run through the whole topic. Learn them first.

The three classes

A lever is named by which of the three parts sits in the middle. Compare them.

Match the parts

Name the class

In which class of lever is the fulcrum in the middle, between the effort and the load?

• First-class lever
• Second-class lever
• Third-class lever
• No lever works that way

Match the class

Which class is best?

A mechanical advantage above 1 means a lever can move a large load with less effort, which suits a second-class lever like a calf raise. It does not always mean better. A third-class lever has a mechanical advantage below 1, so it needs more effort, but it gives a large range and speed of movement at the end of the limb. That is exactly what a thrower or a kicker wants.

Two athletes, opposite needs

A calf raise and a javelin throw want opposite things from a lever. Rising onto the toes shifts a heavy body a short way, so the useful arrangement has a mechanical advantage above _____, which is the _____-class lever. A throw wants the hand moving as fast as it can, and that comes from a value below 1, which costs more _____ but buys _____ where the hand releases the javelin. So a figure below 1 is not a _____: it is the right trade for the job.

Third-class levers

Which statements about third-class levers are true? Choose all that apply.

• The effort is between the fulcrum and the load
• They are the most common lever in the body
• They give a large range and speed of movement
• They have a mechanical advantage above 1
• The load is in the middle

Find the second-class levers

Tap the two actions that use a second-class lever.

• Standing up onto tiptoes
• A calf raise onto the balls of the feet
• A bicep curl at the elbow
• Nodding the head at the neck

Work out the advantage

A lever has an effort arm of 60 cm and a load arm of 20 cm. Mechanical advantage is the effort arm divided by the load arm. What is its mechanical advantage? Give a number.

Order the method

Put the steps to work out mechanical advantage in order.

• Identify the fulcrum, the effort and the load
• Measure the effort arm and the load arm from the fulcrum
• Divide the effort arm by the load arm
• Decide if the value is above 1 or below 1

Classify the action

Read each sporting action and choose the class of lever.

• A player rises onto the toes at the ankle to jump, with the body weight as the load in the middle. Which class of lever is this?
• A thrower flexes the elbow, with the biceps effort in the middle between the elbow and the weight in the hand. Which class of lever is this?
• A player nods the head, with the fulcrum at the neck in the middle between the effort and the load. Which class of lever is this?

Explain the levers

Explain the three classes of lever and what mechanical advantage means.

• Name each class and say which part is in the middle
• Give an example from the body or sport for each class
• Say what mechanical advantage means and how it is worked out