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Lifter: What Is a First-Class Lever, and What Is The Advantage of Using One?

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Author: Janice VanCleave

Problem

What is a first-class lever, and what is the advantage of using one?

Materials

• lightweight table
• sturdy chair (the back should be as tall as the table)
• broom

Procedure

1. Put one hand under the edge of the table (be sure there's nothing on it) and gently push upward. Try to lift the end of the table off of the floor. Warning: Do not strain if the table is heavy.
2. Place the back of the chair about 4 inches (10 cm) from the edge of the table.
3. Lay the broom handle over the back of the chair and under the edge of the table.
4. Place your hand on the straw end of the broom and gently push down.

Results

The end of the broom handle rises, lifting the table off the floor. Using the broom to raise the table takes less effort than trying to lift the table with your hand.

Why?

Machines are often thought of as complicated devices with many moving parts that are powered by a motor. Scientists define a machine as any device that changes either the direction or the amount of force that you must apply to accomplish a task. The broom acts as a kind of simple machine called a lever. A lever is a rigid bar that pivots around a fixed point called a fulcrum. There are three different kinds of levers: first-class, second-class, and third-class. One type is not superior to another; each just has the fulcrum in a different place.

The broom in this experiment is an example of a first-class lever, which always has the fulcrum (in this case, the chair back) between the effort force (the push or pull needed to move an object) and the load (the object being moved).

A first-class lever changes the direction of the force; one end of the lever moves up when the other is pushed down. With this type of lever, less effort force is used when the effort arm (the distance from the fulcrum to the point where you apply the effort force) is longer than the load arm (the distance from the fulcrum to the load). Because your force was multiplied by the lever, it was easier to move the table with the lever than with your hand. Second-class and third-class levers are explained in Experiments 2 and 3.

Let's Explore

1. Would the position of the fulcrum (the chair back) affect the results? Repeat the experiment, placing the chair at different distances from the edge of the table. Science Fair Hint: Use diagrams to represent the different positions of the fulcrum. Indicate which positions require the most and the least amount of effort to lift the table.
2. Would the length of the lever affect the results? Repeat the original experiment twice, first replacing the broom with a shorter rod, and then with a longer rod.

Show Time!

1. Put one end of a pencil under a stack of books. Use a second pencil as a fulcrum by placing it under the first pencil. Push down on the end of the first pencil and try to lift the books. Move the fulcrum closer to, and then farther away from, the stack of books and try again. Display diagrams that show the fulcrum in different positions, and describe how easily the books were lifted each time.
2. Observe and make a list of some common and important uses of first-class levers in daily life. Some examples are:
• playing on a see-saw.
• using a hammer to pull out a nail.
• using a tree branch to lift a rock
• using a screw driver to pry the lid off a paint can.

Photographs and diagrams of these and other examples of first-class levers make a good project display.

Check It Out!

Find out about Archimedes, an ancient Greek scientist and mathematician, who first defined the principle of levers. What did he mean when he said "Give me a place to stand and I will move the earth"? Discover how he pulled a heavily loaded ship along the beach single-handedly.