Lever Classes and Mechanical Advantage
Levers turn muscle force into movement at your joints. Learn the three classes of lever, how to spot which part is in the middle, and how to work out mechanical advantage.
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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.
Words to know
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
- Fulcrum
- Load
- Effort
- Mechanical advantage
- The fixed pivot point, which is a joint
- The resistance or weight being moved
- The force applied by the contracting muscle
- The effort arm divided by the load arm
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
- First-class lever
- Second-class lever
- Third-class lever
- Effort arm
- The fulcrum is in the middle, as when nodding the head
- The load is in the middle, as when standing on tiptoes
- The effort is in the middle, as in a bicep curl
- The distance from the fulcrum to the effort
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.
Complete the passage
A lever turns around a fixed pivot called the _____. The force from the muscle is the _____. In a second-class lever the load is in the _____. A third-class lever gives a large _____ and speed of movement. Mechanical advantage is the effort arm divided by the load _____.
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
An interactive activity.
Work out the advantage
An interactive activity.
Order the method
An interactive activity.
Classify the action
An interactive activity.
Explain the levers
An interactive activity.