## Balanced Students

### Albert BaggottSanta Rosa District Schools

#### Description

Students use a hands-on activity to investigate the relationships between weights and the distance of the weights from the fulcrum in a balanced 1st class lever.

#### Objectives

The student solves single- and multi-step linear equations and inequalities that represent real-world situations.

The student knows that simple machines can be used to change the direction or size of a force.

#### Materials

-Meter sticks
-Supports
-Balance support
-Knife-edge lever clamps
-Weights to hang on meter stick (fishing sinkers, bolts, paper clips)
-Activity Sheet (See Associated File)

#### Preparations

1. Copy and duplicate sufficient quantity of the Activity Sheets from the associated file.
2. Get out meter sticks, supports, knife-edge clamps, weight hanger clamps and weights/weight containers. (Containers such as plastic beakers may be suspended from the hangers with weights placed in them as well.) These supplies are available from most scientific supply houses.

#### Procedures

NOTE: This lesson is concerned only with first class levers having only two weights.

1. Set up and balance a first class lever using a meter stick, balance support, knife-edge clamp and two equal weights. When students see you set up the apparatus it will probably stimulate their curiosity and get their attention. Tell them this is a first class lever because the weights (forces) are on opposite sides of the fulcrum (support). Give some everyday examples of 1st class levers (claw hammer, pry bar, jack handle, pliers, scissors).

2. Tell students that levers are simple machines because they have one or no moving parts and can change the direction or amount of force required to move objects.

3. Ask students what they think is the relationship between the two distances of the weight from the fulcrum. Let students discuss.

4. Ask students if other settings will work. Let students discuss.

5. Ask students if it is possible to balance two unequal weights. Let class discuss.

6. Divide students into groups. Pass out lever apparatus and Activity Sheets. (See Associated File)

7. Instruct students to balance two equal weights at two different positions and two unequal weights at two different positions and to record data. (See Directions on Activity Sheet) If weight hangers are used, they must be included as part of the weight.

8. Let students perform calculations, distance from fulcrum x weight (torque). Ask students to compare the results for each balanced set. Most will recognize that the product of the distance of the weight from the fulcrum on one side of the lever is equal to the product of weight and the distance from the fulcrum on the other side of the lever.

9. Ask students to formulate a general equation for this relationship. Reinforce by writing the equation on the board. D1W1=D2W2 Point out to students that an equation is analogous to a balance or lever. Changes on one side require appropriate compensation on the other side to maintain balance (equality).

10. Let students attempt to solve a problem in groups, such as predict an unknown weight. (See Problems on Activity Sheet)

11. Allow one student who has the correct answer to put the problem on the board.

12. Repeat the procedure for more problems.

#### Assessments

Evidence:
The student is able to solve a problem concerning a first class lever.

Criteria:
1. The student sets up an equation correctly showing that torques on each side of a fulcrum are equal.
2. The student correctly solves the equation.

This is a formative assessment and students may need additional practice before showing mastery.

#### Attached Files

This file contains the Activity Sheet and related answers.     File Extension: pdf