Children on teeter-totter

Children on teeter-totter (axel2001, iStockphoto)

Simple Machines - Levers

Let's Talk Science

Summary

The lever is a type of simple machine. Learn about the different classes of levers and how they provide mechanical advantage.

Simple machines are mechanical devices that are used to make work easier. Combinations of two or more simple machines working together are called compound machines. These machines create systems for different kinds of movement to occur when force is applied to a load. Both simple and compound machines make work easier by changing the size or direction of the force. There are six standard types of simple machines. They are the:

  • Lever
  • Wheel and axle
  • Pulley
  • Inclined plane
  • Wedge
  • Screw

Let us consider the first of these simple machines: the lever.

Misconception Alert

When you hear the word “machine” do you automatically think of something with a motor, like a forklift or a washing machine? Machines do not have to have motors. In fact, a machine is any device that transmits or modifies force.

What is a Lever?

A lever is a simple machine made of a rigid beam and a fulcrum. The effort (input force) and load (output force) are applied to either end of the beam. The fulcrum is the point on which the beam pivots. When an effort is applied to one end of the lever, a load is applied at the other end of the lever. This will move a mass upward. Levers rely on torque for their operation. Torque is the amount of force required to cause an object to rotate around its axis (or pivot point).

What is mechanical advantage?

A lever provides mechanical advantage. Mechanical advantage refers to how much a simple machine multiplies an applied force. The location of the effort, load, and fulcrum will determine the type of lever and the amount of mechanical advantage the machine has. The farther the effort is away from the fulcrum, the easier it is to move the load.

Mechanical advantage can be calculated using this formula:

Mechanical advantage is equal to the ratio of the effort to the load as well as to the distance from the effort to the fulcrum to the distance from the load to the fulcrum
Mechanical advantage is equal to the ratio of the effort to the load as well as to the distance from the effort to the fulcrum to the distance from the load to the fulcrum (©2020 Let’s Talk Science). 

If the distance from the effort to the fulcrum is greater than the distance from the load to the fulcrum, then the lever has a mechanical advantage. In other words, the ratio of these two distances is greater than one. This means that a long distance from the effort to the fulcrum and a short distance from the load to the fulcrum will allow a small effort to move a large load!

Basic parts of a lever showing the locations of the beam, fulcrum, effort and load
Basic parts of a lever showing the locations of the beam, fulcrum, effort and load (© 2019 Let’s Talk Science). 

First Class Levers

There are three types, or classes of levers. 

In a first class lever, the fulcrum is located between the load and the effort.

In a first class lever, the fulcrum is located between the load and the effort
In a first class lever, the fulcrum is located between the load and the effort. When the fulcrum is closer to the load, then less effort is needed to move the load (©2020 Let’s Talk Science). 

If the fulcrum is closer to the load, then less effort is needed to move the load a shorter distance. If the fulcrum is closer to the effort, then more effort is needed to move the load a greater distance. A teeter-totter, a car jack, and a crowbar are all examples of first class levers. First class levers are very useful for lifting large loads with little effort.

First class levers include scissors (left), teeter-totters (centre) and crowbars (right)
First class levers include scissors (left), teeter-totters (centre) and crowbars (right) (Sources: Thamizhpparithi Maari [CC BY-SA 3.0] via Wikimedia Commons, Tiia Monto [CC BY-SA 3.0] via Wikimedia Commons and Pearson Scott Foresman [Public domain] via Wikimedia Commons).

Second Class Levers

In a second class lever, the load is located between the effort and the fulcrum.

In a second class lever, the load is located between the effort and the fulcrum.
In a second class lever, the load is located between the effort and the fulcrum. When the fulcrum is closer to the load, then less effort is needed to move the load (©2020 Let’s Talk Science). 

If the load is closer to the fulcrum than the effort, then less effort will be required to move the load. If the load is closer to the effort than the fulcrum, then more effort will be required to move the load. A wheelbarrow, a bottle opener, and an oar are examples of second class levers. 

Second class levers are used in wheelbarrows (left), when going on tiptoes (centre) and when doing push-ups
Second class levers are used in wheelbarrows (left), when going on tiptoes (centre) and when doing push-ups (Sources: MarkusHagenlocher [CC BY-SA 3.0] via Wikimedia Commons, BruceBlaus [CC BY-SA 4.0] via Wikimedia Commons and U.S. Navy [Public domain] via Wikimedia Commons).

Third Class Levers

In a third class lever, the effort is located between the load and the fulcrum. 

In a third class lever, the effort is located between the load and the fulcrum.
In a third class lever, the effort is located between the load and the fulcrum. If the fulcrum is closer to the load, then less effort is needed to move the load (©2020 Let’s Talk Science). 

If the fulcrum is closer to the load, then less effort is needed to move the load. If the fulcrum is closer to the effort, then the load will move a greater distance. A pair of tweezers, swinging a baseball bat or using your arm to lift something are examples of third class levers. These levers are useful for making precise movements. 

Examples of third class levers
Third class levers are used when swinging a tennis racquet (left), in staple-removers (centre) and when you lift objects using the muscles in your biceps (right) (Sources: Australian Paralympic Committee [CC BY-SA 3.0] via Wikimedia Commons, Frank C. Müller [CC BY-SA 4.0] via Wikimedia Commons and John Seb Barber [CC BY 2.0] via Wikimedia Commons).

Levers are very useful simple machines used for transferring force. You may not realize it, but you use levers every day!

 

References

Afework, B., Hanania, J., Stenhouse, K., & Donev, J. (2018, May 18). Lever. Energy Education.

Curley, R. (2017, June 26). Simple machines. Encyclopaedia Britannica.

Jones, A. Z. (2019, July 20). How does a lever work and what can it do? ThoughtCo.

SoftSchools.com (2019). Levers.

Woodford, C. (2019, August 5). Tools and simple machines. Explain That Stuff.