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The Three Classes of Levers

By — John Wiley & Sons, Inc.
Updated on Dec 13, 2010

Lots of Levers and Lots of Class

Levers are simple machines that have a rigid arm around a fixed point or fulcrum. Force is transferred from one part of the arm to another. The input (effort) force is multiplied or redirected into an output (resistance) force. Levers are divided into three different classes. A first-class lever has the fulcrum between the input and output forces. A second-class lever has the output force between the fulcrum and the input force. The third-class lever has the input force between the fulcrum and the output force. In this activity you will sort different types of levers into their appropriate classes.

The Three Classes of Levers

Materials

An envelope containing pictures or illustrations of ten different types of levers

Photocopy ten or more pictures of levers in action for your students.  Cut these pictures apart and place them in envelopes so that each student has ten pictures representing different types of levers.  Suggestions inlcude a wheelbarrow, a screwdriver prying off the lid of a paint can, a batter hitting a baseball, a person sweeping, a hinged nutcracker, a claw hammer pulling out a nail, scissors, tweezers, a hinged door, and a teeter-tooter or seesaw.  Be sure to include a picture of a wheelbarrow with a mound of dirt or sand in it, because you will use this image in this activity.

White piece of paper

Magic marker

Glue or tape

Activity

  1. Empty the envelope full of pictures of levers on a table.
  2. Divide the white paper into three columns. Title the columns ''First Class,'' ''Second Class,'' and ''Third Class.''
  3. Determine the location of the fulcrum, input force, and output force on each picture. Use the marker to write F, I, and O on the pictures at the appropriate locations. Glue each of the pictures in the proper column for the class of lever it represents. Following is one example:
    1. You have a picture of a wheelbarrow.
    2. The fixed point or fulcrum is at the wheel. Write F on the wheel.
    3. The input force is where you lift the handles of the wheelbarrow. Write I at the ends of the handlebars.
    4. The output, or resistance force, is the load in the wheelbarrow. Write O on top of the load.
    5. Look at the location of the F, I, and O. Notice that the O is between the F and the I, which tells you that a wheelbarrow is a second-class lever.
    6. Glue this picture under the second-class lever column.
  4. Repeat these steps for the remainder of the pictures.

Follow-Up Questions

  1. Which items were the first-class levers? Second-class levers? Third-class levers?
  2. Which of the classes were the easiest to identify? Why?

Answers

  1. Answers will vary depending on the pictures the teacher chooses. In the examples given in the Teacher's Notes, the first-class levers are the screwdriver prying up the lid, the claw hammer removing a nail, the scissors, and the teeter-totter. The second-class levers are the wheelbarrow, the nutcracker, and the hinged door. The third-class levers are the baseball batter, the person sweeping, and the tweezers.
  2. Answers will vary, but most students will say first-class levers are easier to identify.

Extension

Look at your pictures and your list and answer the following questions. Which class of levers always multiplies force? Which class always increases distance? Which class can either multiply force or increase distance?

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