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Levers - Balancing

Name of Corresponding Unit Plan: Levers - Seesaw

Grade Level: K-8

Content Areas: Science

Recommended Length/Duration: 30-50 minutes

Learning Goals:

Primary – Students will discover that a lever can be balanced in a variety of ways.  A longer lever requires a smaller weight to balance a heavier weight on a shorter lever.

Intermediate – Students will recognize the mathematical relationship between the length of the lever arm X the resistance weight.

Description/Sequence

  1. The teacher will describe the components of a lever system and how to set it up:
    • Lever arm
    • Fulcrum
    • Resistance weights
  2. The teacher will explain the data that is to be recorded on the data collection worksheet.
  3. Students will work in groups or individually to create a variety of balancing systems.
  4. Students will record on their data sheet the weights and distance from the fulcrum for each side of the lever system.
  5. After testing a variety of systems, students should answer the questions on the worksheet.
  6. When groups are finished, the teacher should lead a discussion about their findings.  Guiding questions might include:
    • Did every system balance?
    • Were you able to balance a heavy weight with a lighter weight?
    • Were you able to balance a short lever arm with a long lever arm?
    • What is the relationship between the length of the lever arm and weight?
    • Is there a mathematical relationship between the length of the lever arms and weight in a balancing system?
    • What other combinations would create balancing lever systems?

Materials/Resources Balancing Levers Worksheet (pdf); rigid rulers at least 30 cm long, a triangular or round fulcrum, a set of science weights or a collection of uniform objects (unifix cubes, sugar cubes, pennies, etc.)

Special Considerations It can be difficult to get a lever to balance exactly; close is generally close enough to make the point.  Also levers should not swing too high from the desk top.  A 30 cm wooden ruler balanced on a pencil is usually good.  Be sure students read the measurement of the lever arm from the center of the weight.  Older students should obtain data that will yield the formula: Weight 1 X Distance 1 = Weight 2 X Distance 2.  This is the basic formula for finding the mechanical advantage of any lever system.