39. Newton's First Law of Motion



13. Newton's First Law of Motion

May the Force Be with You

Driving Question

What can a force do to an object’s motion?

Materials and Equipment

For each student or group:

|Data collection system |PAScar or other cart or toy car |

|Force sensor with hook and rubber bumper |Duct tape or packing tape, several strips |

|Motion sensor |Metric ruler or meter stick |

Safety

Add this important safety precaution to your normal laboratory procedures:

■ Do not apply a pushing or pulling force greater than 50 newtons to the force sensors (doing so will result in damage to the sensors).

Thinking about the Question

The word force is used in everyday language in many different of ways. In physical science, a force is a push or a pull on an object. When describing forces, it is important to include the strength, or magnitude, of the push or pull. In other words, forces can come in every size imaginable.

It is also important to include the direction of the push or the pull when describing forces. If you have ever played soccer, football, basketball, or any sport that uses a ball, you know perfectly well that the ball has to travel in the correct direction if you hope to score! Baseball and softball players know how important both strength and direction are when they are batting. If they hit the pitched ball with a large enough force, they may send that ball right over the wall…but the ball’s direction could send it just a few centimeters over the foul line!

Most people have had experience pushing or pulling objects. Discuss with your lab group members some examples of forces you commonly encounter each day. As you list examples, try to include both the strength of the force as well as its direction. For instance, if you use a bowling ball as an example, include the direction it rolls as well as how hard it has to be rolled to get successfully to its targets.

Sequencing Challenge

The steps below are part of the Procedure for this lab activity. They are not in the right order. Determine the proper order and write numbers in the circles that put the steps in the correct sequence.

Investigating the Question

Note: When you see the symbol "�" with a superscripted number following a step, refer to the numbered Tech Tips listed in the Tech Tips appendix that corresponds to your PASCO data collection system. There you will find detailed technical instructions for performing that step. Your teacher will provide you with a copy of the instructions for these operations.

Part 1 – Making predictions

1. ( Write your predictions for the following:

a. What will happen to an object such as a toy car if no one touches it?

b. What will happen to a toy car if someone pulls it from the right?

c. What will happen to a toy car if someone pulls it from the left?

2. ( Write your predictions for the following:

a. What will the graph of position versus time look like for a toy car being pushed gently toward the motion sensor?

b. If the force sensor is attached to the car, and you pull on the force sensor hook, what will happen to the graph of force versus time?

c. What will the motion and force graphs look like if no one pushes or pulls on the toy car?

Part 2 – Investigating pushing and pulling a cart

3. ( Start a new experiment on the data collection system. �(1.2)

Sensing motion

4. ( Connect the motion sensor and the force sensor to the data collection system. �(2.2)

5. ( Display Position on the y-axis of a graph with Time on the x-axis.

Note: Make sure the selector switch is set to the cart icon.

6. ( Position the cart approximately 50 cm from the metal screen of the motion sensor.

7. ( Start data recording. �(6.2)

8. ( Slowly and steadily push and pull the cart so it travels as follows:

a. Push the cart toward the motion sensor, stopping about 15 cm in front of the metal screen.

b. Pause for five seconds.

c. Pull the cart back to the beginning position.

d. Pause for five seconds

e. Push the cart toward the motion sensor, stopping again about 15 cm in front of the metal screen.

9. ( Stop data recording.

10. ( Observe the graph of position versus time. Describe your graph.

11. ( Print your graph according to your teacher's instructions. � (11.1)

12. ( Attach the force sensor to your cart.

[pic]

Note: If you use tape, be sure to secure the sensor firmly so it does not move when you pull on the hook.

13. ( Why do you think the force sensor needs to be attached so securely? How might your data look different if the sensor were loosely attached or able to move while you push or pull it?

Sensing force

14. ( Zero the force sensor.

Note: The force sensor always needs to be zeroed in the position it will be used.

15. ( Display Force on the y-axis of a new graph with Time on the x-axis. �(7.1.1)

Note: You do not need to display motion for this part of the activity.

16. ( Position the cart approximately 50 cm from the metal screen of the motion sensor.

17. ( Begin data recording. �(6.2)

18. ( Firmly grasp the hook of the force sensor, and steadily push and pull the car as you did in the first trial—toward the motion sensor, stop for 5 seconds, away from the motion sensor, stop for 5 seconds, and then toward the motion sensor, stopping about 15 cm in front of the metal screen.

[pic]

19. ( Stop data recording. �(6.2)

20. ( Observe the graph of force versus time. Describe your graph.

Part 3 – Measuring force and motion

21. ( Display two graphs simultaneously. On one graph, display Force on the y-axis and Time on the x-axis. On the second graph, display Position on the y-axis and Time on the x-axis. �(7.1.11)

22. ( Begin data recording. �(6.2)

23. ( Position the cart approximately 50 cm from the metal screen of the motion sensor.

24. ( Begin data recording. �(6.2)

25. ( Firmly grasp the hook of the force sensor, and steadily push and pull the car as you did in the first trial—toward the motion sensor, stop for 5 seconds, away from the motion sensor, stop for 5 seconds, and then toward the motion sensor, stopping about 15 cm in front of the metal screen.

26. ( Stop data recording. �(6.2)

27 ( Again position the cart approximately 50 cm from the metal screen of the motion sensor.

28. ( Begin data recording. �(6.2)

29. ( Now push and pull the cart through the same series of motions as you did previously, but this time change the speed so that the cart travels faster or slower than in previous trials.

30. ( Stop data recording. �(6.2)

31. ( Observe the graph. Record your observations.

Answering the Question

Analysis

1. How did your predictions from Part 1 compare to the results in Part 2?

2. Describe the car’s motion when no force is applied to it.

3. Sir Isaac Newton said, “Every body persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.” By body he meant “any object,” including a toy car. What do you think Newton meant by “a state of rest,” and by “uniform motion?”

4. If we re-state Newton’s idea from question #3 above, so it sounds more modern, we might say, “Every object standing still stays standing still, and every object that is moving keeps on moving, unless some outside force acts upon that object.” Suppose Newton was referring to the cart you just used in Part 2 and Part 3 of this investigation. What outside forces acted upon your group’s cart?

5. What evidence do you see in your graphs of position and force versus time that supports Newton’s idea?

6. How could you re-state, or paraphrase, Newton’s idea, also known as Newton’s First Law of Motion, in your own words?

Multiple Choice

Select the definition that best defines the given word.

1. Push

A. How far away an object is from a reference point

B. The SI unit measure for length

C. One of the two types of force

D. A unit used to measure force

2. Pull

A. A push or pull exerted on an object

B. A unit used to measure force

C. One of the two types of force

D. A unit used to measure mass

3. Newton

A. The SI unit of measure for force

B. A change in the position or place of something over time in comparison to a reference point

C. One of the two types of force

D. The law that states that an object will remain at rest or in uniform motion unless acted on by an outside force

4. Motion

A. How far away on object is from a reference point

B. One of the two types of force

C. A change in the position or place of something over time in comparison to a reference point

D. The SI unit of measure for length

5. Distance

A. The law that states that an object will remain at rest or in uniform motion unless acted on by an outside force

B. One of the two types of force

C. A push or a pull

D. How far away an object is from a reference point

6. Force

A. A unit of measure for mass

B. A change in the position or place of something over time in comparison to a reference point

C. The SI unit of measure for length

D. A push or a pull

7. Meter

A. How far away an object is from a reference point

B. A length equivalent to 100 centimeters

C. The unit of measure for force

D. A unit of measure for mass

8. First law of motion

A. The law that states that an object will remain at rest or in uniform motion unless acted on by an outside force

B. One of the two types of force

C. A change in the position or place of something over time in comparison to a reference point

D. The SI unit of measure for length

Key Term Challenge

Fill in the blanks from the randomly ordered words below:

|meter |newton |motion |sensor |

|body |magnitude |distance |force |

|first law of motion |push |direction |pull |

1. One of the two types of force is .

2. The law that states that an object will remain at rest or in uniform motion unless acted on by an outside force is the .

3. Another of the two type of force is .

4. The SI unit of measure for length or distance is .

5. SI unit of measure for force is .

6. A push or a pull is a .

7. How far away an object is from a reference point is called .

8. A change in the position or place of something over time in comparison to a reference point is called .

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Make certain that each member of your lab group is aware of the safety rules and procedures for this activity.

Connect force and motion sensors to the data collection system. Attach a force sensor to the GOcar or dynamics cart.

Connect force and motion sensors to the data collection system and begin data recording.

Press the zero button on the force sensor once it is in position, to orient it in the earth's gravitational field.

Apply a series of pushes and pulls to the cart and analyze the resulting graphs.

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