Name_______________________________Date____________________________

PRE-LAB FOR INTRODUCTION TO MOTION(Due at the beginning of the Lab)

Directions: Download the general lab instructions, read this lab, and answer the following questions:

2. For the motion detector to make an accurate measurement, what is the minimum distance it can be from an object?

3. What is the name of the port that connects the motion detector and the Labpro interface?

4. How does the Logger Pro software determine whether the direction of motion is positive or negative? Why is there no negative position?

5. What does the “Store Latest Run” feature do?

Lab Group Members: Date:

Discovery Lab: Introduction to Motion With Logger Pro

Purpose: Introduction to Logger Pro system, the motion detector; and graphical analysis of motion

Equipment: Laptop computer, LoggerPro Software, Motion detector, Black USB cable,Gray printer cable, 1-2 metersticks

Introduction: In this investigation, you will use a motion detector to plot a position-time graph of your motion.

The motion detector is the origin from which positions are measured. Since it cannot “see” objects behind it, it can only plot positive position. It can, however, show both positive and negative displacement, velocity and acceleration. The default setting is that motion away from the detector is positive and motion towards the motion detector is negative.

It detects the closest object directly in front of it. It will not correctly measure anything closer than 0.20 meter. When making your graphs, don't go closer than 0.20 meter from the motion detector.

Logger Pro Setup1. Plug the motion detector into any USB port of the computer with the black cable.

2. Use the wide beam setting (person/ ball).

3. Open the Logger Pro program (red caliper icon on desktop). Open the file Away and Back, L01A1-1b, (File – Open - Experiments- Additional Physics- Real Time Physics – Mechanics).

4. Answer any dialog boxes; if asked, confirm that you want to use a motion detector.

5. When you are ready to start graphing position, click once on the Collect button on the toolbar. If you have a number line (meterstick) and you want the detector to produce readings that agree, stand at the 1-meter mark on the number line and have someone move the detector until the reading is 1 meter. See instruction sheet for additional tips on data acquisition. 6. Store latest run: Use this feature of the software so that the graphs you just made are persistently displayed and you cannot accidentally erase them. Go to “Experiment” on the toolbar and choose “Store Latest Run” from the drop-down menu.

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Investigation 1: Position - Time GraphsActivity 1 Make position-time graphs for different walking speeds and directions.

Clear lab tables of backpacks and books Don’t swing your arms or bounce up or down while walking. If you get a straight horizontal line, the detector isn’t seeing you.

Adjust detector and beam direction. If you see big spikes on the data, the beam is hitting a chair, floor,

or ceiling before the walker. Adjust beam position and/or detector. “Steadily” means at a constant speed. Don’t speed up or slow

down.

a. Start at the 1/2-meter mark and make a

distance/time graph, walking away from the

detector (origin)

Sketch the graph on the right.

D i s t m

T i m e (sec)

slowly and steadily.

b.

T i m e (sec)

Make a distance/time graph,

walking away from the detector

(origin)

Sketch the graph.

D i s t m medium fast and steadily.

D i s t m

c. Make a distance/time graph,

walking toward the detector

(origin)

Sketch the graph.T i m e (sec)

d. Make a distance/time graph,

walking toward the detector

(origin)

Sketch the graph.T i m e (sec)

D i s t m

slowly and steadily.

medium fast and steadily.

3

Questions 1. Describe the difference between the graph you made by walking away slowly and the one made by walking away more quickly.

___________________________________________________________

___________________________________________________________

2. Describe the difference between the graph made by walking toward and the one made walking away from the motion detector.

___________________________________________________________

___________________________________________________________

Prediction 3. Predict the graph produced when a person starts at the 1-meter mark, walks away from the detector slowly and steadily for 4 seconds, stops for 4 seconds, and then walks toward the detector quickly (but still at a constant speed). Compare predictions with the rest of your group. See if you can all agree. Draw your group's prediction on the left hand axes using a solid line. (Do not erase your original prediction.)

4. Do the experiment. Move in the way described and graph your motion. When you are satisfied with your graph, draw your group's final result on the right axes.

5. If your prediction did not result in the answer you expected, describe how you would move to make a graph that looks like your prediction. ___________________________________________________________

___________________________________________________________

___________________________________________________________

Activity 2 Non-Linear Position- Time GraphsCan you make a curved position-time graph? Try to make each of the graphs

shown below.

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1. Describe how you must move to produce a position-time graph with each of the shapes shown.

Graph A answer:______________________________________________

___________________________________________________________

___________________________________________________________

Graph B answer:______________________________________________

___________________________________________________________

___________________________________________________________

Graph C answer:______________________________________________

___________________________________________________________

___________________________________________________________

2. How is motion for a curved graph different than for a linear graph?

_____________________________________________________________

_____________________________________________________________

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Activity 3 Equation of a Line

Make a linear position vs. time graph as before. Direction isn’t important, but it should be linear starting at t=0 (start walking before the program starts graphing). When you get a good graph, store latest run to keep data displayed and PRINT your graph to the printer (Attach to lab)

1. Find the equation of the line your walking produced. Do not use the linear fit function:

Equation: _____________________________________________

Explain what you did to find the equation:

2. What are the units of the slope? _________

Your equation should be the format: x = mt + b, where m is the slope and b is the “y”-intercept. Explain what m and b actually tell you about the moving object.

m ____________________________________

b _____________________________________

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Investigation 2: Velocity-Time Graphs

Activity 1 Making Velocity Graphs1. Open the experiment file called Velocity Graphs, L01A2-1 (File – Open

- Experiments- Additional Physics- Real Time Physics – Mechanics)..

2. Graph your velocity for different walking speeds and directions.

a. Make a velocity graph by walking away from the detector slowly and steadily (i.e. constant speed). Repeat until you get a graph you're satisfied with.

Note: Keep your arms by your sides and shuffle your feet to minimize “bounce”. It may be helpful to hold a notebook against you to provide a flat area.

Sketch your result below. (Just draw smooth patterns; leave out bumps that are mostly due to your steps.)You may want to enlarge the velocity axis to get the “big picture”.

b. Make a velocity graph, walking toward the detector slowly and steadily. Sketch your graph.

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Questions 3. How does the shape of velocity vs time graphs differ from those of position vs. time graphs for the same motion (i.e. constant speed)? ______________________________________________________________________________________________________________________________________________________________________________________

4. How are the velocity-time graphs different for motion away and motion toward the detector?

___________________________________________________________

___________________________________________________________

Activity 2 Where did I start?

Prediction Explain how you can tell from a velocity-time graph where you were, relative to the motion detector, when you started walking and where you were when you stopped?

On the bottom graph, draw a velocity graph for someone walking at about 0.5 m/s away from the motion detector, starting at 0.5 meters away from the motion detector. Then draw a graph (different color or dashed line) to show someone walking away at the same velocity that started at 1 meter away from the motion detector.

Velo

city

(m/s

)

Time (seconds)4 8 12 16 20

-1

+1

0

0

. . . . .

. . . . .

. . . . .

. . . . .

-

-

-

- - - - -

Set up the motion detector and test your prediction. Make a graph walking away from the motion detector. Use the store latest run feature from the

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“Experiment” menu so that the graph will remain persistently displayed on the screen. Then make a second graph moving at the exact same speed, but this time start at a different distance from the motion detector. Sketch the two graphs below:

Velo

city

(m/s

)

Time (seconds)4 8 12 16 20

-1

+1

0

0

. . . . .

. . . . .

. . . . .

. . . . .

-

-

-

- - - - -

Question 1. Is there anything on the graph that indicates starting position? What is your conclusion regarding obtaining position information from a velocity-time graph?

Investigation 3: Position and Velocity Graphs

Activity 1 Predicting Velocity Graphs from Position Graphs1. Predict a velocity graph from a position graph. Open the experiment file

Velocity from Position, L01A3-1. Carefully study the position graph shown below and predict the velocity-time graph that would result from the motion. Using a dotted line, sketch your prediction of the corresponding velocity-time graph on the velocity axes.

2. Make the graphs. After each person has sketched a prediction, do your group's best to make a position graph like the one shown below. Walk as smoothly as possible to minimize steps.

When you have made a good duplicate of the position graph, sketch your actual graph over the existing position-time graph.

Use a solid line to draw the actual velocity graph on the same graph with your prediction. (Do not erase your prediction).

3. Store latest run: Use this feature of the software so that the graphs you just made are persistently displayed and you cannot accidentally erase them. Go to “Experiment” on the toolbar and choose “store latest run” from the drop-down menu.

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Activity 2 Determining Mean Velocity from a Velocity Graph and from a Position Graph

1. Select the non-zero portion of the velocity graph and use the Statistics function to find the average velocity while you were moving:

Average velocity:________ m/s

2. Select the corresponding portion of the position graph, and use the Linear Fit function to find the equation of your motion during that time interval:

slope of the position-time graph:________ m/s

3. Are these values equal (i.e. within .1 m/s of each other)? Explain why they should be (if yours are not, make sure you are selecting the correct portion of each graph).

4. Print and attach your graph with the boxes showing average velocity and linear fit .

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5. In Investigation 2, you determined that you couldn’t obtain position information from a velocity graph. Can you obtain velocity information from a position graph? If so, what information and how?

6. Write a general equation (symbols only) to describe the position (x) of an object with constant velocity, v and initial position, x0:

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Activity 3 More Position GraphsSketch the position time graph corresponding to each of the following descriptions of the motion of an object.

1. The object moves away from the origin with constant velocity.

2. The object is at rest.

3. the object moves toward the origin with constant velocity for 5 seconds and then stands still for 5 seconds.

4. The object moves with a steady velocity away from the origin for 5 seconds, reverses direction and moves at the same speed toward the origin for 5 seconds.

5. The object moves away from the origin, speeding up as it moves.

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Answer the following about two objects, A and B, whose motion produced the following graphs. For these questions, the word “ahead” refers to the object that is out in front in the direction of motion

6a. Which object is moving faster?_____

6b. Which starts ahead?_______

6c. What does the intersection mean?

________________________________ _______________________________

7a. Which object is moving faster?_____

7b. Which object is moving in a negative direction?

8a. Which object is moving faster?_____

8b. Which starts ahead (i.e. out in front)?

_______

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Activity 4: Velocity-Time GraphsAfter studying the velocity-time graphs you have made, answer the following questions:

0

+V e l

Time

-1. How do you move to create a horizontal line in the positive part of a velocity-time graph?

_____________________________________________________________

_____________________________________________________________

V e l

Time0

+

-

2. How do you move to create a straight-line velocity-time graph that slopes up from zero?

_____________________________________________________________

_____________________________________________________________

TimeV e l

0

+

-

3. How do you move to create a straight-line velocity-time graph that slopes down?

_____________________________________________________________

______________________________________________________________

TimeV e l

0

+

-

4. How do you move to make a horizontal line in the negative part of a velocity-time graph?

________________________________________________________________

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5. The velocity-time graph of an object is shown below. Figure out the total displacement of the object. Show your work.

Displacement = ____________ meters.

2 4 6 8 10

-4

V e l o c i t y

m/s

+4

00

. . . . .

. . . . .

. . . . .

. . . . .

T i m e (s e c)-

-

- - - - -

+2

-2

6. Both of the velocity graphs below, 1 and 2, show the motion of two objects, A and B. Answer the following questions separately for 1 and for 2. Explain your answers when necessary.

a) Is one faster than the other (exclude t=0s)? If so, which one is faster, A or B?b) What does the intersection mean?c) Can one tell which object is closer to the motion detector? If so, which one is closer at t=0 s, A or B? d) Which object, A or B, is moving in a negative direction (i.e. towards the motion detector)? How can you tell?

1 2

V E L

T I M E0

V E L

T I M E0

A

B

B

A

a._________________ a.____________________

b. __________________ b. __________________

_____________________ ____________________

c. ___________________ c.____________________

d.____________________ d.___________________

______________________ _____________________

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Sketch velocity-time the velocity -time graph corresponding to each of the following descriptions of the motion of an object.

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11. Draw the velocity graphs for an object whose motion produced the distance-time graphs shown below on the left. Distance is in meters and velocity in meters per second. (That is, the velocity is the number of meters the object would move in one second.)

Note: Unlike most real objects, you can assume these objects can change velocity so quickly that it looks instantaneous with this time scale (i.e. vertical velocity lines are ok).

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12. Draw careful graphs below of distance and velocity for a cart that—a. moves away from the origin at a slow and steady (constant) velocity for the first 5

seconds.b. moves away at a medium-fast, steady (constant) velocity for the next 5 seconds.c. stands still for the next 5 seconds.d. moves toward the origin at a slow and steady (constant) velocity for the next

5 seconds.e. stands still for the last 5 seconds.

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