Begin the Investigation by reviewing the experiments students completed in Investigation One and conclusions they have drawn about the concept of force. 

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The following questions may help involve students in the discussion:

What types of experiments did you perform in Investigation One? What was the purpose of the experiments? Students performed experiments in which they used a spring scale to measure the force exerted by solids, liquids, and gases. The purpose of the experiments was to investigate what is meant by the term “force”, to determine whether there was a difference in the force exerted to lift loads of different masses and to determine whether solid, liquid, and gaseous states of matter exert force.

What does the term force mean? The application of a constant effort, such as a push or pull.

What is the scientific representation for force? Force is represented in equations and formulas as the capitalized letter “F”

What have you learned about force so far? Is your understanding of force different now than when we started the CELL? How? [At this time, you may wish to show students their ideas about force that you recorded in the Pre-lab section of Investigation One and discuss how their ideas may have changed.] Students should indicate they have learned that the amount of force exerted on a load increases as the mass of the load increases. They should also understand that all three states of matter – solids, liquids, and gases – exert force.

Can you give examples of when force is used to move an object? Student answers may vary. Examples may include walking across the room, swinging a baseball bat, rolling a ball, or pushing or pulling a chair away from a table.

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Explain to students that in addition to force, this and other Investigations in the CELL will also involve the concept of work.

Ask students whether they have heard or used the term work. Encourage students to share some of their own ideas about work and situations in which they encountered or used the word work to describe an event. Students may reply with suggestions such as the chores they must do at home, the assignments from school they must complete at home, their parents’ jobs, a work of art, etc.

Explain to students that the term work, like the term force, can have a variety of meanings in everyday life, but in science, the term has a specific meaning.

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Direct students to reference their Scientist’s Glossary. Ask students: What is the definition for the term work?

“A measure of the distance (d) over which a force (F) is applied. Work is represented mathematically by the formula Work = Force × distance (W = Fd).”

As you introduce the work formula, discuss what is meant by the term formula and how the formula for work is related to the mathematical concepts of equations and multiplication. The questions that follow may help during the discussion:

Ask students: Have you used equations involving multiplication to calculate numbers or quantities? It is likely that students will have had previous experiences in which they used equations that involved multiplication.

How would you explain the following equation to your friend?

2 × 5 = 10

Student answers will vary. Students may state that two multiplied by five equals ten. Or they might say that two times 5 is equal to 10, etc.

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What if you were given the following problem? How would you solve the problem? Carlos had five bags from the grocery store. Each bag contained two oranges. How many oranges did Carlos have? Students should suggest that the number of bags would be multiplied by the number of oranges per bag. If this were done, the total number of oranges would be ten.

Write the following equation on the board as you discuss the answer to the word problem. Direct students’ attention to the concept that both the simple number problem and the word problem involved the multiplication of two quantities.

Two oranges in a bag × five bags = 10 oranges

Explain to students that if you worked in the store and needed to create a rule or way to tell other people in the store how to calculate oranges every time oranges were placed in bags you might use the equation below. 

Number of oranges × number of bags = total number of oranges

The equation represents oranges and bags in general terms so that even if different numbers of oranges and bags are used, each person would know how to calculate the number of oranges.

Often when an equation describes a rule or a general way to calculate a quantity, the equation is called a formula. The equation above would represent a formula for calculating the total number of oranges.

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Direct students’ attention to the formula for work, discussing the individual variables that comprise work and helping students to understand the relationship between the symbols in the formula and the way in which the formula is restated in the definition of work in their Scientist’s Glossary. Pose the following questions to students during the discussion:

Which two quantities are multiplied to calculate work? Force and distance.

How might you restate the formula for work in words? Work equals force multiplied by distance, or work is performed when a force is applied over a distance.

Think about the experiments you performed in Investigation One. How can you measure force? Which metric units of measurements are used when measuring force? In Investigation One we measured force using a spring scale. Force was measured in units of Newtons.

Which metric units are used to measure distance? Students should suggest that distance can be measured in units of centimeters, meters, millimeters, or kilometers.

• Explain that when calculating work, distance is generally recorded in the units of meters.
• Discuss how specific measurements of force and distance can be used to calculate work by going through the story problem and formula shown on this slide. Be sure to explain that the metric units used when describing the amount of work performed are joules (J).

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Ask students the following questions to help relate the concepts of work and force to actions that occur in everyday life. Discuss the following information with students, writing the main terms from the Scientist’s Glossary on the board as you discuss them (students may reference their glossary during the discussion):

Ask students: What would you need to know to calculate how much work was done if you moved a book across the desk? Student answers may vary. Students should suggest that they would need to know the distance the book was moved and the amount of force that was applied to move the book.

Ask students: How would you measure the distance the book was moved? Distance (d) can be measured using the metric system. A metric ruler or meter stick with the metric units of centimeters (cm) or meters (m) could be used.

Ask students: What would you use to measure the force exerted to move the book? A spring scale.

Ask students: Do you remember when you lifted the load in Investigation One? Did it feel easier or harder when you lifted the load a larger distance? Students will likely suggest lifting the load farther felt harder.

Think about your results from Investigation One. Did the force needed to lift the load change when it was lifted farther? No.

If the force was the same, why did it feel harder to lift the load farther? Can any of the new information about work help you answer this question? Student answers may vary. Students may not suggest that the distance the load is lifted may require more work. If this occurs, encourage students to think about the question as they perform their experiments and come back to the question after the experiments are completed.

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Tell students that they will conduct experiments in Investigation Two. As they conduct their experiments they will be asked the following questions: 

• How does the force and distance a load is lifted affect the amount of work performed on the load?

• How can the work done to lift a load be decreased?

• How can the work done to lift a load be increased?