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Work and Simple Machines

Investigation 1 – Lab

Back to Investigation 1

BE PREPARED

Group materials:

3 100 g masses
1 triple beam balance
1-liter pitcher filled with tap water

Pair materials:

1 spring scale
1 white plastic bucket
1 meter stick
1 100 ml graduated cylinder
1 straw
2 paper towels

Individual materials:

1 Student Data Record

Teacher Preparation

1. Fill a liter pitcher with water for each group.

2. Place the materials each pair will need at a distribution point.

3. Separate the class into pairs.

4. Position student pairs around five lab tables or desks.

5. Place three (3) 100 g masses, one (1) triple beam balance, and one (1) liter pitcher filled with water at each table.

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Instruction

Direct each student pair to obtain the following necessary materials from the distribution point: one (1) spring scale, one (1) white plastic bucket, one (1) 100 ml graduated cylinder, one (1) meter stick, and two (2) paper towels.

1. Explain that, in this investigation, students will use a new tool from their Procedural Toolbox, the spring scale. Students will use the spring scale to explore force, one of the components that determine work. The passages that follow are provided to assist your direction of the students through this part of the Investigation and through the introduction to the new tool.

a. Introduce the spring scale as a scientific tool that can be used to measure force (Figure 1.1a).

• Tell student groups to examine their spring scale.

• Ask students to observe that the spring scale has two different scales – each directly opposite the other.

Note: The spring scale has two scales. The side marked with an “N” at the top of the scale measures the force produced by a load in newtons (Figure 1.1b). The side marked with a “g” at the top of the scale measures the mass of the load in grams (Figure 1.1c). However, in this CELL, the spring scale will only be used by students to measure force.

b. Explain to students that before using the spring scale, it should be calibrated. The indicator platform of a calibrated spring scale is positioned at the “zero” graduation. Encourage students to complete the following steps to calibrate the spring scale before measuring force:

• Turn the spring scale so that the newton scale is visible. Hold the spring scale by the handle with the “0” graduation of the newton scale directly at eye level.

• If the indicator platform is not lined up with the 0 N graduation, calibrate the spring scale by rotating the adjustment nut at the top. Turning the wheel clockwise raises the platform. Turning the nut counterclockwise lowers the platform.

c. Direct students to perform a test of the spring scale. Place a load, one plastic bucket, onto the hook of the spring scale (Figure 1.2a). Measure the force exerted on the load using the newton side of the spring scale. Each small line, or graduation, on the scale, represents 0.1 N. Remember that the numbers on the spring scale increase as they go down the scale.

d. Tell students that the end of the spring scale’s hook should fit through the hole in the bucket handle (Figure 1.2b). Students should hold the spring scale and bucket so they hang free of any other objects.

e. Students can measure the force exerted on the bucket by examining the position of the indicator platform.

GET FOCUSED

Students will continue to explore the use of the new tool from their Procedural Toolbox, the spring scale. They will be asked two questions to help them become more familiar with the spring scale.

What are the different parts of the spring scale?

Which part of the spring scale is used to measure Force (F) in the metric units of newtons (N)?

INVESTIGATE

Trial 1

Students will investigate whether solids can exert a force by lifting a load consisting of a bucket and a 100 g mass, both solid objects. They will use a spring scale to obtain a quantitative measurement of the force exerted on the load. Students will be asked two questions as they investigate the relationship between force and solids:

Is a force exerted by solids?

How much force is exerted on a bucket that contains a 100 g mass, a solid object?

Trial 2

Students will investigate whether a liquid can exert a force by lifting a load consisting of a bucket and 100 ml of water. They will use a spring scale to obtain a quantitative measurement for force exerted on a load. Students will be asked two questions that are the main focus of this part of the investigation and make a prediction based on one of the questions:

Is a force exerted by liquids?

How much force is exerted on a bucket that contains 100 ml of water?

Encourage students to make a Prediction by asking: Do you think that the bucket with 100 ml of water will require the same force to lift as the bucket with the 100 g mass?

Trial 3

Students will investigate whether a gas can exert a force by measuring the force of air exhaled from a student’s lungs. They will use a spring scale to obtain a quantitative measurement for force. Students will be asked two questions during this part of the investigation and will make a prediction based on those questions:

Can gas exert a force?

How much force will your partner exert when he or she blows into the bucket?

After students have completed Trials 1, 2, and 3, direct them to review the data they collected from each trial and to use their results to answer the following question.

Which states of matter can exert force?

Trials 4, 5, and 6

Students will continue to explore force by investigating how the mass of a load affects the amount of force exerted to lift the load. To conduct their experiments, student pairs should combine so that five student groups are formed.

In their experiments, students will use a spring scale to obtain a quantitative measurement for the force exerted to lift several loads. Students may notice that in the previous set of experiments they were asked to determine “the force exerted on the load,” where as in this set of experiments they are asked to determine “the force exerted to lift the load.” In both sets of experiments, students move the spring scale with the attached load a certain distance at a constant velocity. As a result, the force exerted on the load is equal to the force exerted by a person to lift the load. In the first set of experiments, the focus was on the force exerted by different states of matter, while the focus of the second set of experiments is the force exerted by a person to lift a load. Thus students are presented questions about force in two different ways.

Students will begin Trials 4 through 6 by performing the same steps as in Trial 1, but will use increasingly larger loads, each time determining the force required to lift the load. Student investigations will be prompted by asking students a question about the relationship between mass and the force needed to lift a load.

How would changing the mass of the load affect the force exerted to lift the load?

As students conduct their experiments, it may be helpful to periodically ask student groups several leading questions to aid their investigation of the larger question about mass and force.

How much force was exerted on the load?

Is this the same force as the other loads?

Do you see a pattern between the mass of the load and the force exerted on the load?

Encourage students to describe their Prediction as a rule, for example: “The more mass, the more force is required to lift it.”

After students have completed Trials 4, 5, and 6, direct them to take several minutes to review the data they collected from their experiments. The students should use their experimental results to describe their observations and answer a question that is an important focus in this investigation.

Did you see a pattern between the mass of the loads in Trials 4, 5, and 6 and the force exerted to lift the loads?

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Optional Extension: Students will be asked a question that they should discuss and analyze within their group. Students should be permitted several minutes to accomplish this task and record the results.

Does the same relationship between mass and force exist with the other states of matter? If so, how could you test it?

Upon completion of the experiment, permit enough time to clean up the lab and return the materials and equipment to their assigned location.