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Second-Class: What Is a Second-Class Lever, and What is The Advantage of Using One?

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Author: Janice VanCleave

Problem

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

Materials

• Scissors
• yardstick (meterstick)
• string
• brick

Procedure

1. Cut a 1-yard (1-m) piece of string.
2. Tie one end of the string around the brick, and place the brick on the floor.
3. Hold the free end of string, and lift the brick about 6 inches (15 cm) above the floor.
4. Observe the effort required to lift the brick.
5. Place about 2 inches (5 cm) of the end of the yardstick (meterstick) on the edge of a table.
6. Tape the end of the stick to the table.
7. Set the brick on the floor directly beneath the midpoint of the stick.
8. Lower the free end of the stick, and tie the free end of the string around the center of it.
9. Lift the free end of the stick until the brick is about 6 inches (15 cm) above the floor.
10. Compare the effort it takes to lift the brick using the string with the effort needed to lift it by raising the stick.

Results

It takes less effort to lift the brick by raising the end of the yardstick (meterstick) than lifting it with the string.

Why?

The yardstick (meterstick) acts as a kind of simple machine called a second-class lever. A lever is a rigid bar that pivots around a fixed point called a fulcrum (as in Experiment 1). A lever is considered second-class when the load (the object being moved-in this case, the brick) is between the fulcrum and the effort force (the force you applied to the stick). A second-class lever does not change the direction of the force; the load moves in the same direction as does the effort force (the brick moved in the same direction as your hand-up). This type of lever, while not as effort-saving as a first-class lever, still requires less force to raise the load than if you lifted it without the lever.

Let's Explore

1. Would the position of the load affect the results? Repeat the experiment, first moving the brick close to the end of the yardstick (meterstick) that is supported by your hand, and then moving the brick near the end that is taped to the table.
2. Would the position of the effort force affect the results? Repeat the original experiment, holding the stick closer to the load (the brick). Science Fair Hint: Display diagrams representing the positions of the fulcrum, resistance arm, and effort arm. Indicate the effort required to lift the load in each position.

Show Time!

What is a second-class lever? Give more than a definition of the term. Observe and discover common examples of second-class levers in the world around you, such as a wheelbarrow, a nutcracker, and a bottle opener. Photographs taken of the observed examples of second-class levers can be displayed.

Check It Out!

A wheelbarrow is an example of a second-class lever. It is known as an independent invention—that is, the wheelbarrow was designed in different places at different time periods. Find out more about this useful lever. What were the early wheelbarrows used for? Why was the European wheelbarrow not as efficient as the wheelbarrow designed by the Chinese?