Three classes of lever

The idea

Levers are of three classes by the relative positions of effort, fulcrum and load: Class I has the fulcrum in between, Class II the load in between, and Class III the effort in between.

Scissors, wheelbarrow, tweezers

Scissors, a wheelbarrow and tweezers are all levers, but the fulcrum, the load and the effort are arranged differently in each.

What do you think could be used to sort levers into classes?

• The position of the effort, fulcrum and load
• The colour of the lever
• The material of the lever

Sort the levers

Put each lever in its class.

Who sits in the middle

The three classes differ in which of the three, fulcrum, load or effort, lies between the other two.

Levers are of three classes, depending on the relative positions of effort, fulcrum and load: Class I has the fulcrum in between, Class II the load in between, and Class III the effort in between.

• Class I | Class II | Class III
• Relative position | Fulcrum in between | Load in between | Effort in between
• Examples | Seesaw, scissors, crowbar | Wheel barrow, bottle opener, lemon squeezer | Tweezers, broom, oar

Notes

Class I: fulcrum in between. Class II: load in between. Class III: effort in between.

Check yourself

In a Class I lever, which one is in between the other two?

A wheel barrow is a Class II lever. What is in between?

In a Class III lever, the part in between the other two is the…

Which of these is a Class I lever, according to the book?

• The load. That is a Class II lever.
• The fulcrum — correct. Yes!
• The effort. That is a Class III lever.
• The fulcrum. That is a Class I lever.
• The effort. That is a Class III lever.
• The load — correct. Yes!
• effort — correct. Yes!
• fulcrum. That is a Class I lever.
• load. That is a Class II lever.
• Tweezers. The book lists tweezers as a Class III lever.
• A seesaw — correct. Yes!
• A bottle opener. The book lists a bottle opener as a Class II lever.