Levers: First-Class Machines

A lever is a simple machine with a rigid arm that turns about a fixed point called a fulcrum. A first-class lever can be used to help lift a heavy object. This type of lever has the fulcrum located between the effort force, force applied to lift an object, and the resistance force, force created by the weight of the object that needs to be lifted. In this activity you will find out how the location of the lever's fulcrum affects the force required to lift an object.

Materials

Stiff ruler; Small book; Pencil; Masking tape

Activity

1. Place a pencil on a table so it is horizontal to you. Tape the pencil to the table.
2. Place the ruler at a right angle across the top of the pencil so it acts like a teeter-totter or seesaw. The point where the ruler touches the pencil is the fulcrum.
3. Position one edge of a small book so it rests on one end of the ruler.
4. Arrange the ruler so that the fulcrum is six inches from the edge of the book. Push down on the effort end of the lever (the end opposite the book) to lift the book. Your push is the effort force. How difficult was it to lift the book?
5. Arrange the ruler so that the fulcrum is nine inches from the book. Push down on the effort end of the lever to lift the book. How difficult was this?
6. Arrange the ruler so that the fulcrum is three inches from the book. Push down on the effort end of the lever to lift the book. How hard was this to lift?

Follow-Up Questions

1. What is the difference between effort force and resistance force?
2. How did the distance of the book from the fulcrum affect the effort needed to lift the book?

Answers

1. Effort force is applied to the lever to move an object. Resistance force is due to the weight of the object.
2. The greater the distance, the less force needed to move the object.

Extension

Stack six pennies on one end of a twelve-inch ruler. Place three pennies on the other end. Where must the fulcrum be located in order to make the ruler balance when placed on a pencil?