The Lever

A lever is a stiff shaft that rotates on a pivot, called the fulcrum.  To explore a lever, use a ruler as the shaft and a marker or small piece of wood as the fulcrum.  Try lifting a weight with the fulcrum in different places.  You will find that the farther you have to move the part of the lever where you push, the less force you will have to use.  Of course, if the effort moves with less force, it will be moving farther and the load will be moving less distance.
 

Let's say you want to use a lever to move a very heavy rock.  You might set the lever up as follows:
 

 

Remembe, work is defined as force x distance.  Simple machines can make work easier or more convenient, but they don't change the total amount of work done.  Thus, in the image above, the rock can be lifted will little effort, because the force of this effort is acting over a long distance.  Notice how far you would move (Distance) compared to how far the rock moves (distance).  Using the lever makes the force go down and distance go up -- but their product remains the same.  If you compare the use of the lever to lifting the rock directly, you will see that lifting it directly requires a large EFFORT (force), over a short distance:


There are three classes of levers, depending upon where the fulcrum, the resistance and the effort are in relation to one another.

First Class Lever (e.g. see-saw)
 

 

Second Class Levers (e.g. wheelbarrow)


 

Third Class Levers (e.g. catapult)


 

Your fingers are levers too.  Notice how you can't break a match placed at the end of your fingers (picture on the left) but you can if placed back towards your hand (picture on the right).  You can break the match when the resistance is closer to the fulcrum (the joint at your hand).
 


 

Other examples of levers:


©2001 Jeff Goodman

Back to ASU Science and Science Teaching in the Elementary School Home Page