The Motion Detector measures the time it takes for a high frequency sound pulse to travel from the detector to an object and back. Using this round-trip time and the speed of sound, the interface can determine the distance to the object; that is, its position. It can then use the change in position to calculate the object’s velocity and acceleration. All of this information can be displayed in a graph. A qualitative analysis of the graphs of your motion will help you understand the concepts of kinematics.
Objective
- Understand the relationship between shape of kinematics graphs and the motion that produced them
Materials
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Macintosh or Windows Computer |
meter stick |
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Logger Pro or Logger Lite |
masking tape |
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Motion Detector or Go! Motion |
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Procedure
1. Find an place to locate your motion detector that has an open area at least 4 m long in front of it. Use short strips of masking tape on the floor to mark distances of 1 m, 2 m, and 3 m from the detector.
2. If your Motion Detector (or Go! Motion) has a switch, set it to Normal as shown on the right. Connect the Motion Detector to DIG 1 of LabPro (or connect the Go! Motion to the computer with the USB cable). Launch Logger Pro or Logger Lite and choose New from the File menu. If you have an older sensor that does not auto-ID, you will need to manually set up the sensor.
3. In Logger Pro, open the file in Physics with Vernier: "01a Graph Matching". If you are using Logger Lite, open the file in Middle School with Vernier: "33a Graphing Motion".
4. In Logger Pro, click on the "stopwatch" icon. (In Logger Lite, click on Experiment > Data Collection…) In the window that appears, change the data-collection length to 10 seconds. Click on [Done] to set this new collection time.
Part l Preliminary Experiments
5. Stand in front of the motion detector and monitor the position readings on the Setup screen as you move back and forth. Confirm that the values make sense.6. Make a graph of your motion when you walk away from the detector with constant speed. To do this, stand about 1 m from the detector and start data collection. Walk backward, slowly away from the detector after data collection begins.
7. How will you know you have obtained a good graph? When you get a good graph, describe the shape of that graph.
8. Once you get a good graph, in Logger Pro click on Experiment > Store Latest Run store that run. In Logger Lite, click on the file cabinet icon in the menu bar. You are now ready to collect a second run.
9. What will the distance vs. time graph look like if you were to walk backwards at a faster speed? Check your prediction by repeating step 6 but walking backward a bit faster.
10. How can you tell the difference between the first and second run? What differences were there between the two graph lines? Can you begin to draw some conclusions about the shape of position vs. time graphs and what they might indicate about your motion?
11. When you are finished with this part, click on Data > Clear All Data.
Part Il Making Position vs. Time Graphs
12. In the spaces below, you will see a series of graphs on the left-hand side. Using your Motion Detector, move until you have created a graph that matches the shape of the one shown. On the right-hand side, describe how you moved in order to create that graph.
