Position & Velocity:
Can You Relate?

Experiments from Team Labs

Experiment Profile

Connections:		Distance (Position) and Velocity Measurement, Technology, Mathematics
Skills:		Predicting, Modeling, Measuring, Graphing, Analyzing
Duration:		1 Class Period
Team Size:		2-3 students per group
Content Standards:		Science Standard A (grades 9-12) Science Standard B (grades 9-12) Science Standard E (grades 9-12) Math Standard 1, 2, 3, 4, 5, 6, 10, 11, 13, (grades 9-12)

Purpose

• To help students understand how a Distance Probe works.
• To make predictions based upon story problem scenarios.
• To model experimentation that mirrors predictions.
• To analyze data and graphs, learning the relationships between Distance and Position as well as Velocity and Position, as related to time.

Summary

In this experiment, you will be required to formulate predictions and determine outcomes that will be produced when using a Distance Probe. You will make predictions first, then try to simulate and mirror those predictions with relation to your position to the Distance Probe and how fast or slow you move when attempting to model the scenarios presented to you.

Materials

• Computer
• ThinkStation Interface
• Power Supply
• Communications Cable
• Excelerator 2000 Software
• Distance Probe
• Distance Probe Module (yellow Motion & Mechanics box)
• Ring stand, or similar fixed position device (clamped rod, the wall -- using Velcro to affix the probe, etc.)

Background

The Distance Probe uses the same technology that Polaroid Cameras and similar devices use to measure the distance to an object. In the case of the camera, the distance-sensing device allows the camera to use the appropriate settings to take a focused and normally exposed picture. The Distance Probe uses this technology to make similar calculations with an accuracy of ± 7 mm over its entire temperature range (0 ºC to 52 ºC).

The range of the Distance Probe is 0.4 m to 10 m; therefore, certain considerations must be taken into account when making your predictions to ensure you create scenarios that can be measured accurately. Your Distance Probe uses ultrasonic pulses (sound) to measure the time it takes to send out a pulse and wait for that sound wave to bounce off an object and return to the source-the Distance Probe. Knowing the speed of sound, the software is able to calculate any object's position, velocity, and/or acceleration.

In this experiment, you will be asked to reproduce a number of Distance vs. Time graphs while walking back and forth in front of the Distance Probe. To begin this experiment, make yourself familiar with and practice using the Prediction Line in Excelerator. This is one of the functions of the right mouse button that allow you to analyze your graph data.

Show me

Note: Since the temperature of the air affects the speed of sound, make sure you measure the temperature of your classroom or lab (you could use the Standard or Extended Temperature Probes, or a classroom thermometer in degrees Celsius) and input that value in the Distance Probe's calibration dialog box. The default setting is 22 ºC (which may indeed be the temperature of your room, in which case you would not need to change this setting).

Procedure

Collecting Data with the Distance Probe

1. Prepare your experiment by first affixing the Distance Probe to something that will put it in line with your chest as you stand -- a ring stand with rod, a rod clamped to a table, or Velcro-type tape attaching the probe to the wall, etc. Plug the Distance Probe into the yellow Motion & Mechanics Module, and insert the module into one of the two right rear module ports on the Thinkstation interface. Your chest will serve as the reflecting surface that the probe will use to make its calculations.
Show me	2. Launch Excelerator 2000 and click on the Connect&GOTM icon. Excelerator will automatically identify the Distance Probe and create a Position vs. Time Graph. You will need to edit a few parameters before beginning. The software will set default sample rates and durations for the experiment, which you will change in the next step.
	3. To change the sample rate and duration of the experiment, click on the Edit Clock icon located on the Excelerator toolbar.
Show me	Set the sample rate to 20 samples per second and the duration to 15 seconds.
Show me	4. Create a Prediction Line similar to the one shown at left by right-clicking in the grid portion of the Fast Graph and choosing Prediction Line. Note the Time and Position (distance) measurement units.
5. Once you have made your prediction, position yourself with relation to the probe in the position that you feel represents the time at 0 seconds.
	6. You will now attempt to model the scenario you have created as a pre-trial prediction line. When you feel you are in the appropriate starting position, ask your teammate to click the GO button. As you watch the screen of your computer, attempt to place yourself in the position/s that will make your actual real-time trial data mirror your prediction line.
View screen	7. At left is the actual data produced when we attempted to model this scenario. Is movement necessary? How difficult is it to stay in one position?
View screen	8. Next, note the following Position scenario. Again, create a Prediction Line that is similar to the one shown at left prior to attempting to model it.
	9. Model your Prediction Line by positioning yourself in front of the Distance Probe. When you are ready, ask your teammate to click the GO button. * Practice modeling your Prediction Line until you nearly mirror the trend line showing in your Fast Graph for this scenario. Did you start at the correct position? Were you able to model your prediction line on the first try? How many trials were needed to closely mirror the Fast Graph's Prediction Line?
View screen	10. Again, at left is our attempt at such a scenario.
11. Now, based upon the following story problem, create a Prediction Line that will model it. (Create your prediction from the following description in words without relying on our picture model.) This Position scenario asks you to model the following: A. Start from a fixed position that is at the probe's lower range limit, 0.4 m, and remain there for 2 s. B. At 2 s, rapidly move to a position that is 2 m from the probe over the course of 1 s, and then hold steady there for 2 s. C. Gradually return to a position that is 1.5 m from the probe over the course of 4 s. D. Without pausing, lean your chest in, then out, with 1 s pauses between leans, then remain in a fixed position at a distance of 1.5 m.
View screen	12. The screenshot at left shows a possible Prediction Line based upon the previous story problem.
13. After exploring Position with the Distance Probe, you will now explore Velocity. Click on the Distance Probe icon in the y-axis area (or click Edit Experiment in the Experiment toolbar, and change the measurement setting to "Velocity") and remove the Position measurement.
View screen	14. With Excelerator ready to measure Velocity using the Distance Probe, create a Prediction Line based upon the model at left.
15. As the focus of this experiment has shifted from Position to Velocity, re-focus your predictive notions in your attempt to model them based upon the definition of Velocity -- the change in position over the change in time, or: ΔP/ΔT
View screen	16. Our attempt produced the results shown at left. Is a Velocity of 2 m/s or 1 m/s easier to model in a short amount of time? Why? What movement (forward or backward) when using velocity is considered positive or negative (above or below 0)? How does this relate to how the probe makes measurements?
17. Create your own Velocity-based story problem for your teammates to attempt to model. Keep in mind the probe's limits and the limits of your own body movements over time (e.g. can you really move 5 m/s under your own foot power in a mere 1-second period? Not likely!)
18. Exchange scenarios with a teammate. Make a Prediction Line of the story problem posed to you.
19. Model your prediction and record this data.

Analysis of the Data

Analyze your Fast Graphs, noting your ability or inability to mirror the predictions you created.

• What was the most difficult scenario to predict?
• What was the most difficult scenario to actually model?
• What changes did you have to make in your predictive nature when switching from Position measurements to those of Velocity?
• Why is the Distance Probe sensitive to temperature?

Conclusions

As you should have discovered, the Distance Probe is very sensitive to your movements. This is why there is a tendency to see actual data look a little "choppy" and errant as you try to mirror predictions, for they can be hard to model in a very consistent manner. Practice makes perfect in these scenarios. More than one attempt is usually necessary to correct your behavior of movements before being able to closely model the prediction line with accuracy. This will also help you to correct your misconceptions about distance, position, velocity and movement in general.

When you have mastered the use of the probe for the measurements requested in this experiment, attempt scenarios using the Acceleration measurement from the Distance Probe. This concept requires more patience and exploration to fully understand, as it is usually more difficult to mirror in real-time with body movements. Try using frictionless cart systems for more reproducible results. The sky's the limit in your investigation of these concepts. In the case of the Distance Probe, your limit is about 10 meters!

Extensions

Use probeware to investigate the following:

• Predict the movement of other items and how they will affect the Distance Probe, such as a skateboard going up or down an incline.
• Have two students attempt to model a prediction at the same time, standing side by side, to see if they follow the same pattern as they attempt to model a scenario put up on the screen as a Prediction Line. (They may tend to follow one another incorrectly and/or show misconceptions as they relate to how the probe takes measurements, especially as related to positive or negative values).

About the author... Marc Mueller is the Secondary Curriculum Specialist at Team Labs. His background includes packaging and mechanical engineering, secondary science, technology and vocational instruction. His real-world experience is mirrored in his curricula as he has been focused on engineering, creating applied technology laboratories, and the creation of pre-engineering, computer technology and vocational coursework and activities throughout his career.

If you have a great experiment idea, please send mail to the webmaster.

Download a PDF of this experiment (746 KB)

Top
	| Home | What's New | Products | Resources | Support | Training | Contact Us |
Site Map | Copyright and Legal

© Copyright 2004, EyeThink Corporation.