Exploratories

Making Distance-Time Graphs

Problem:

How can you measure your motion with a motion detector?

How will your motion look as a distance-time graph? In this investigation, you will use a motion detector to plot a distance - time graph of your motion. As you walk (or jump, or run), the graph on the computer screen displays how far away from the detector you are.

a. "Distance" is short for "distance from the motion detector."

b. The motion detector is the origin from which distance is measured.

c. It detects the closest object directly in front of it (including your arms if you swing them as you walk).

d. It will not correctly measure anything closer than .5 meter. When making your graphs don't go closer than .5 meter from the motion detector.

e. To focus better the ultrasonic beam that comes out of the motion detector, remove the bottom off of a standard Styrofoam cup and tape the cone around the motion detector opening. Holding a piece of poster board in front of your body provides a uniform reflecting surface and will give better graphs.

Materials:

TI Graphing Calculator and CBL system or MacMotion software (Motion for MS-DOS) Universal Laboratory Interface (ULI) or MBL equipment, a motion detector.

In this investigation, you will use a motion detector to plot a distance-time graph of your motion. As you walk (or jump, or run), the graph on the computer screen displays how far away from the detector you are.

a. "Distance" is short for "distance from the motion detector."

b. The motion detector is the origin from which distance is measured.

c. It detects the closest object directly in front of it (including your arms if you swing them as you walk).

d. It will not correctly measure anything closer than .5 meter. When making your graphs don't go closer than .5 meter from the motion detector.

e. To focus better the ultrasonic beam that comes out of the motion detector, remove the bottom off of a standard Styrofoam cup and tape the cone around the motion detector opening.

Procedure:

For using a CBL follow these steps:

1. Run the PHYSICS program on your calculator. (If you do not have this program, you can download it from the Worldwide Web from Vernier at http://www.teleport.com/~vernier.) Make sure the CBL interface is plugged securely into the calculator and the motion detector is connected to the CBL. Make the following selections:

a. Set up Probes

b. One Probe

c. Motion

d. Collect Data

e. Time Graph

f. Non-live Display (for live set-up, Y-scaling should be Ymin = 0, Ymax = 6, and Yscl = 1.

g. Sample time 0.1 s; 99 samples

h. Press [Enter] to go on

i. Use time set up

j. Choose Distance

2. Proceed to step 4 below.

For using the ULI and MacMotion follow these steps:

1. Open the MacMotion program. To start the program, use the mouse to double click on the MacMotion icon. The graph axes should appear on the screen. (Be sure the ULI is connected to the computer and turned on, and the motion detector is plugged into port #2.)

2. When you are ready to start graphing distance, click once on the Start "button" in the bottom left-hand corner of the screen.

3. Adjust the distance reading. If you have a number line and you want the detector to produce readings that agree, stand at the 2-meter mark on the number line and have someone move the detector until the reading is 2 meters.

4. Start at the 0.5-meter mark and make a distance-time graph, walking away from the detector (origin) slowly and steadily. Sketch the graph.

5. Make a distance-time graph, walking away from the detector (origin) medium fast and steadily. Sketch the graph.

6. Make a distance-time graph, walking toward the detector (origin) slowly and steadily. Sketch the graph.

7. Make a distance-time graph, walking toward the detector (origin) medium fast and steadily. Sketch the graph.

Summing Up:

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

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

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. Draw your prediction on the graph with a dotted line.

4. Compare predictions with the rest of your group. See if you can all agree. Draw your group's prediction using a solid line. (Do not erase your original prediction.)