1 - Missouri University of Science and Technology



SEQL Student Pre/Post-Test

7th Grade Science

Answer Key

Mrs. Chatman’s seventh grade science class was learning about how simple machines effect the amount of effort force needed to do work. She asked each student to design an experiment using a simple machine to demonstrate this concept. Paul designed an experiment in which he used pulleys to lift a mass that had a weight of 100 Newtons up a height of 10 cm. He wanted to see if increasing the number of pulleys would reduce the amount of effort force needed to lift the mass. Below are the procedures Paul used.

1. Tie a 2 meter long piece of rope to the mass. Lift the mass up 10 cm and measure the force in Newtons of the gravitational pull on the mass.

2. Use a fixed pulley to change the direction of the force needed to move the mass. Measure and record the force in Newtons needed to move the mass.

3. Add a moveable pulley to the pulley system and lift the mass. Measure and record the force in Newtons needed to move the mass using two pulleys.

4. Add another pulley, for a total of three pulleys. Measure and record the force in Newtons needed to move the mass using three pulleys.

5. Add another pulley, for a total of four pulleys. Measure and record the force in Newtons needed to move the mass using four pulleys.

The diagram below shows how Paul carried out his pulley experiment. Numbers 1-4 show the number of pulleys he used.

[pic]

Answer the following questions about Paul’s experiment.

1. Independent Variable? (Science 7.1.A.b) number of pulleys

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2. Dependent Variable? (Science 7.1.A.b) amount of effort force/pulling force/Force

pulling on the mass

3. Write a testable question that could be the basis of Paul’s scientific investigation.

(Science 7.1.A.a)

Any question that shows the affect of the independent variable on the dependent variable

Examples

Will the number of pulleys reduce the amount of effort force needed to lift the mass?

Will the pulleys make it easier to lift the load?

If I add more pulleys, will the load be easier to lift?

4. Write a hypothesis for the testable question you wrote above.

(Science 7.1.A.a)

Any hypothesis that shows the affect of the independent variable on the dependant variable. The hypothesis must answer the testable question. The hypothesis can be incorrect. The hypothesis should be an If/then statement.

Examples

If the number of pulleys is increased, then the effort force needed to lift the mass decreases.

If more pulleys are added, then the mass will be easier to lift.

If Paul adds more pulleys, then the load will feel lighter,

If Paul adds more pulleys, then the pulleys will not affect the load.

5-6. To make a fair experiment, Paul kept several factors constant during the experiment. List

two factors he should keep the same. (Science 7.1.A.b)

Any two variables that are kept constant for each test.

Examples

Type of pulleys, size of the mass being lifted 100 Newtons, same spring scale, same rope, height the mass is pulled up (10 cm)

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7. Choose the statement about independent and dependent variables that is correct.

(Science 7.1.A.b)

a. The dependent variable is the one variable that is changed in an experiment and the

independent variable is the responder variable.

b. A conclusion cannot be made about what changed the dependent variable unless you only change one independent variable.

c. The independent and dependent variable need to be the same.

d. Many variables can be tested at once so more data can be collected and more

conclusions can be made in less time.

|Force in Newtons Needed to Lift a Mass with a Weight of 100 Newtons up a distance of 10 cm Using Various Numbers |

|of Pulleys |

|Number of Pulleys |Lifting Force (F2) in Newtons |

|1 Pulley (fixed) |100.0 |

|2 Pulleys |50.0 |

|3 Pulleys |33.3 |

|4 Pulleys |25.0 |

8-11. Use the data from the table to construct an appropriate graph on the grid below.

(Science 7.a.B.e; Science 7.1.C.a, Science 7.1.D.a)

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Each of the four items on the graph listed below is worth one point each. Independent variable must be on the bottom. Dependent Variable must be on the left side. Numbers and category labels must be evenly spaced.

Be sure to provide:

- an appropriate title

- a label for each axis with appropriate units

- an appropriate number scale and category labels

- correctly plotted data

Examples

Number of Pulleys vs. Effort Force (N)

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Number of Pulleys vs. Effort Force (N)

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14. How would you classify this type of investigation? (Select one)

a. observing and describing objects, organisms, or events

b. collecting specimens

c. experimenting

d. making observations in nature

e. discovery of new objects and phenomena

f. making models

15. What scientific tool could Paul use to measure the force in Newtons? (Science 1.1.A.b; Science 7.1.B.b,c,d,e)

Sping scale

16. Which simple machine design (number of pulleys) required the least amount of effort force to lift the mass 10 cm? (Science 2.2.F.e)

The four pulley design required the least amount of force to lift the block.

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17. As more pulleys were added, the amount of force required to lift the mass decreased. Look at the diagram and key of the pulleys on the first page. What is the relationship between the distance Paul had to pull the rope in order to lift the mass up 10 cm in relation to the number of pulleys that were used. (Science 2.2.F.C)

a. Paul had to pull the rope farther when more pulleys were used.

b. Paul pulled the rope the same distance each time.

c. Paul had to pull the rope less distance when more pulleys were used.

d. The distance Paul pulled the rope was cut in half each time he added a pulley.

18. Paul did work each time he applied a force and the mass moved. If the mass had not moved when Paul pulled on the rope, would any work have been done? (Science 2.2.F.a)

No

19. Make a prediction about the force in Newtons that would be required to lift the 100 Newton block up a height of 10 cm if 5 moveable pulleys were used.(Science 7.1.C.a)

Correct answers: 20 Newtons or 1/5 of 100 Newtons

Answers may vary. Any answer between 18 Newtons and 22 Newtons could be accepted. Students need to understand that by adding another pulley, the mass would require less force to lift it.

20. Describe a real life situation in which a pulley(s) would be useful. (Science 7.1.D.a)

Answers will vary.

Any answer about lifting or moving a heavy object with the use of a pulley(s) is acceptable.

Examples

To lift a heavy load

To lift a motor out of a car

An elevator

Raising a flag up a flag pole

Raising hay into a barn loft

SEQL Student Pre/Post-Test

7th Grade Science

Scoring Rubric

Points Points

Question # Possible Earned Criteria

1) 1 point _____/(1) Correct answer written

2) 1 point _____/(1) Correct answer written

3) 1 point _____/(1) Question is testable and is about the affect of

number of pulleys on the effort force.

4) 1 point _____/(1) Hypothesis answers the question and guesses the

affect of number of pulleys on the effort force.

5) 1 point _____/(1) At least 1 controlled variable is listed

6) 1 point _____/(1) At least 1 controlled variable is listed

7) 1 point _____/(1) Correct answer selected

8) 1 point _____/(1) Appropriate title is labeled

9) 1 point _____/(1) Label for each axis with appropriate units

10) 1 point _____/(1) Appropriate number scale and category labels

11) 1 point _____/(1) Correctly Plotted Data

12) 1 point _____/(1) Conclusion is about the affect of number of

pulleys on the effort force.

13) 1 point _____/(1) Correct analyzing of student hypothesis in

relation to the data

14) 1 point _____/(1) Correct answer selected

15) 1 point _____/(1) Correct answer written

16) 1 point _____/(1) Correct answer written

17) 1 point _____/(1) Correct answer chosen

18) 1 point _____/(1) Correct answer written

19) 1 point _____/(1) Correct answer written

20) 1 point _____/(1) Any description of using a pulley

Total Points _____/20

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KEY for Pulley Diagram

F2 - Force of Paul pulling the mass up

FL - Force of the pull of gravity on the mass

s - Distance string is pulled to move the mass 10 cm

h - Height the mass is pulled up

N - Newtons

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Effort Force to lift Mass (Newtons)

100

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Effort Force to lift Mass (Newtons)

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