PHYS1401 – General Physics I

Kinesthetic Kinematics

Leader: ___________________ Recorder: __________________________

Skeptic: ___________________ Encourager: ________________________

Materials

Laptop with power adapter

LabPro with cable

Motion Detector with cable

C-clamp for motion detector

Introduction

The purpose of this lab is to develop an intuitive understanding of the graphs of position and velocity as a function of time. An important goal is to differentiate between velocity and acceleration.

Background Information

Our procedure will be to record the position as a function of time using ourselves as the object of study. We will measure our position as a function of time using the LabPro interface and a sonic motion detector. We will control the interface and detector using a software package called LoggerPro.

The sonic motion detector measures distances by making use of the fact that sound travels at a constant speed through the air. The sonic ranger measures position by emitting a brief pulse of ultrasound (frequency = 40,000 Hz) towards a target and then detecting the sound reflected from the target. The sonic ranger determines the time interval that passes between when the pulse of sound is emitted and the reflected sound returns. The distance is determined from d = v_st_r/2, where v_s is the speed of sound, and t_r is the time interval between when the sonic ranger emits a pulse of sound and when it detects the reflected sound. The result is divided by 2 because the time interval represents a round trip for the sound, and is thus double the distance to the target. The speed of sound depends on the temperature, but at room temperature, the speed is approximately 343 m/s.

Procedure

1. Set-up

The experimental set up is shown in figure 1. To set up the apparatus, plug the cable from the motion detector into the socket labeled Dig/Sonic 1 on the LabPro. Verify that the LabPro is plugged into the computer and that it has power. Clamp the motion detector to a chair in a position such that the motion detector has an unobstructed view of you walking towards and away from the detector over a distance of several meters. The motion detector attaches to the clamp via a bushing on the back. Note that the LabPro motion detector will not allow you to measure distances of less than .5 m or greater than about 5 m.

2. Start the Software

LoggerPro controls the equipment with files called experiment files. Follow the instructions given by your instructor to download the experiment file called 1401kinkin.cmb to your computer’s desktop. Double click on the experiment file to start LoggerPro.

3. Test the Set-up

To verify that the apparatus is running correctly, we will make a quick graph of position versus time. The monitor should display a blank graph of Distance versus Time. On the right and above the graph is a small button labeled COLLECT . Click on the collect button. The motion detector should click twice, and then make a continuous clicking sound for 5 seconds during which it is collecting data. Move back and forth in front of the motion detector and verify that it is operating correctly. If not contact your instructor.

Figure 1

Apparatus for this experiment

4. Printing

One last thing we need to do is print our graphs. Click on the Printer Button on the tool bar . You will see a window where you can annotate your graphs such as putting the group members’ names on them and so on. Since many groups will be printing similar graphs you should put in identifying information here. Click OK when you're ready to print.

Report Format

Turn in one report worksheet with attached graphs for each group. Make sure that the name of each person in the group is put on the worksheet.

Report Worksheet

Leader: Reporter: _______

Skeptic: ___________________ Encourager: _________________________

Now that we have got our apparatus working, we will acquire the following pictures.

i) a) Discuss among your group how you should move so that you create a distance vs. time graph that increases with a constant slope.

b) Record the motion that you discussed in part a). Did you move in the correct way to produce the desired graph? If not modify your motion so that you do produce the correct graph.

c) Discuss among your group and then sketch in the space below what you think a graph of the velocity vs. time should look like for this picture? You should pay attention to whether the velocity is positive or negative.

d) After your discussion, click on the next page icon so that the graph of velocity vs. time for your motion is displayed. Compare your prediction in part c) to the graph displayed on the screen. Were you correct? Discuss?

e) After you had started moving, did you accelerate during this motion? Explain. Sketch a graph of what you think the acceleration vs. time should look like for this motion.

f) After your discussion, click on the next page icon so that the graph of acceleration vs. time for your motion is displayed. Compare your prediction in part e) to the graph displayed on the screen. Were you correct? Discuss? The signal will be very noisy. Pay attention to the general trend and not all the bumps and wiggles.

Print and attach the graphs for this motion.

Click on the previous page icon twice to return to the Distance vs. time Graph

ii) a) Discuss among your group how you should move so that you create a distance vs. time graph that decreases with a constant slope.

b) Record the motion that you discussed in part a). Did you move in the correct way to produce the desired graph? If not modify your motion so that you do produce the correct graph.

c) Discuss among your group and then sketch in the space below what you think a graph of the velocity vs. time should look like for this picture? Be specific about the sign (+/-) of the velocity.

e) After you had started moving, did you accelerate during this motion? Explain. Sketch a graph of what you think the acceleration vs. time should look like for this motion.

Print and attach the graphs for this motion.

Fill in the blanks in the following questions.

1) When you walk at a constant velocity the graph of Distance vs. time is a line with a constant ________ .

2) When you walk at a constant velocity the graph of velocity vs. time is a ____________ line.

3) When you walk at constant velocity the graph of acceleration vs. time is a ____________ line with a value of ________.

iii) Open the experiment file called Position Match 1 by clicking on the Open icon , then double clicking on the folder titled Probes & Sensors , then double clicking on the folder labeled Motion Detector and finally double clicking on the file Position Match 1.cmbl. When asked if you wish to save , click on NO.

The idea is to try and move so that you match the graph. Have each member of your group try and match the graph. Print one copy and label on the graph the places where the velocity was positive, negative and zero. Also label on the graph where acceleration occurred.

Attach the labeled graph.

iv) Open the experiment file called Velocity Match. To do so, click on the Open icon. The directory you opened last time will still be chosen. Double click on the file called Velocity Match.cmbl. When asked if you wish to save Position Match 1, click on NO.

The idea is to try and move so that you match the graph. Have each member of your group try and match the graph. Note it doesn’t count if you bump into the table or wall before the time runs out. If you get stuck look at your answer to question 2) above.

Print one copy and label on the graph the places where the velocity was positive, negative and zero. Also label on the graph where acceleration occurred.