What advantage do you get from using a lever?


Targets
At the end of this unit, you should be able to answer the following questions:

1. What are simple machines, and how do they make work easier?

1.1 What advantage do I get from using a lever?

1.2 How do wheels and rollers help move things from place to place?

1.3 What role do wheel and axle systems have in moving vehicles and devices?
2. How can I build machines so they move the way I want?

2.1 How force be used to move a vehicle?

2.2 How can you build a machine or device that moves on its own?

2.3 What is needed to design a safe vehicle?

2.4 How can ideas be shared and designs be compared to build the best moving device possible?
Targets
Why is it so difficult to swat a fly with your hand, but so much easier with a flyswatter?  Those fast little flies always seem to get away if you try to get them with just your hand.  The flyswatter makes our strike much faster, doesn't it?  When you are using a flyswatter, you are using a lever.  Most tools such as hammers, pry bars, and rakes as well as sports items such as racquets, bats, and clubs are levers.
Did you know there are three classes of levers?  To understand those, we need to know the parts of a lever.  Suppose you were trying to move a big boulder.  You might use a lever that looks like this:

The load is the object you are trying to move.  The fulcrum is where a lever pivots.  The effort force is your push or pull on the lever.

Depending on what you want to do with your lever, you might choose one of three classes of lever.

Lever Class

Important Notes

Class 1 Lever


Example: Teeter-totter

  • Fulcrum is in the middle.

  • If you want to move something heavy (force advantage), move the fulcrum closer to the load.

  • If you want to move something faster (speed advantage), move the fulcrum closer to the effort force.

  • If you do not want any advantage, put the fulcrum right in the middle!

Class 2 Lever


Example: Wheelbarrow

  • Load is in the middle.

  • This class of lever is made for lifting heavy things (force advantage).  It does not work well to make the load move faster.

Class 3 Lever


Example: hammer
  • Effort force is in the middle.

  • This class of lever is made for moving things faster (speed advantage).  It does not work well for lifting heavy things.
Choosing a lever for a task depends on what you want to do.  Do you want the lever to increase the amount of force?  That means you want a force advantage.  Do you want the lever to increase the speed of motion?  That means you want a speed advantage.

 Video

Watch this ADLC Digital Lesson on Using Levers.
To get the advantage you want, choose the right lever and adjust it so that it does what you want.