# Balancing

**Name of Corresponding Unit Plan:** Levers

**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 relation ship between the length of the lever arm X the resistance weight.

**Description/Sequence**

- The teacher will describe the components of a lever system and how to set it up:
- Lever arm
- Fulcrum
- Resistance weights

- The teacher will explain the data that is to be recorded on the data collection worksheet.

- Students will work in groups or individually to create a variety of balancing systems.

- Students will record on their data sheet the weights and distance from the fulcrum for each side of the lever system.

- After testing a variety of systems, students should answer the questions on the worksheet.

- 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 **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** Levers should not swing too high from the desk top. A 30 cm wooden ruler balance 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.