Simple Machines - Levers

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:

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!

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.

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.

Second Class Levers

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

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. 

Third Class Levers

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. 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. 

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