Background

Doing science is a way of observing and thinking about natural phenomena with the aim of trying to understand them. Models are human generated representations of natural phenomena. What sets science apart from other human intellectual endeavors is that scientific knowledge is based on experiments and observations with the ultimate authority being nature itself. Scientific knowledge is based on the cumulative work of scientists over the past 300 years. Science is a human activity, and each scientist has his/her own personal style, guided by his/her training, talents, biases, and personality. As a start, your common sense and intuition are highly reliable guides to scientific thinking. As you learn some of the fundamental scientific theories and laws in physics, you can hone your scientific modeling and reasoning skills. Generally, this will involve using scientific theory as well as your own common sense and intuition to interpret your experimental data.

Purpose

1) To learn how to set up and perform an experiment using a Universal Lab Interface (ULI) and a Motion Detector to acquire data.

2) To model and interpret scientific data.

Materials

ULI box	Logger Pro software
Macintosh computer	Motion Detector

Procedure

1) Choose two lab partners and select a lab station with a Macintosh computer. Set up your experiment by plugging your motion detector into port 2 of the ULI box which is connected to the computer. Turn on the ULI box with the switch in the back. Make sure the ULI is "on" before you start up the Logger Pro software.

2) Start up the Logger Pro software application on the computer by double clicking first on the PHS 110 folder on the Macintosh desktop, then double clicking on the Logger Pro folder, finally double clicking on the Logger Pro icon.

3) Set up your computer to run your experiment in Logger Pro by following these steps:

1. Click on "Setup" in the menu bar at the top of the Logger Pro window and scroll down to "Sensors.."
2. When the window appears, choose the icon labeled "Port 2" and then use the pull down menu to select "Motion Detector" as your sensor. Make sure all other ports say NONE and click OK.
3. Set up your Graph Window with a title of Distance vs. Time and appropriately labeled axes. Do this by clicking on the vertical axis labeled "Potential" at the left side of the window. When the dialog box appears, click on the "check" in the check box next to Potential. This will disable that axis label and leave only Distance checked in the dialog box. To delete the "Potential" data column in the table, select Data from the bar menu across the top of the screen and highlight Delete Column -> Potential.

   

4. Click on the button at the top of the screen with a small blue clock. This is the "Data Collection.." button and will allow you to change the settings of the motion detector. When the window appears, click on the "Sampling" tab. The sampling rate determines how often the motion detector takes a reading and also the total time data are collected. Change the sampling rate to something appropriate for the experiment planned. For example, for Experiment 1 you might select an Experimental Length of 3 seconds and a sampling speed of 30 samples/second. This means the motion detector will send out 30 pulses of sound every second, for 3 seconds.

4)To collect data, click the "Collect" button on the menu bar.

1. Listen for a pair of double "clicks" from the motion detector. This is the detector getting ready to take data.

   When the detector begins to quickly click, the motion detector is collecting data (distance and time measurements), storing them in the Data Table on the right of the screen, and plotting the distance vs. time data points at the same time. (Note: the motion detector cannot take meaningful data for objects within 0.5 meter of it.)

   

2. After the experiment has run its course, re-adjust your sampling rate on experiment length by going back to Setup (setup 3a above), if necessary.

5)To change the Title on your graph, or the heading of your Data Table, simply double click on either of these names in the Table Window, and edit the pop-up box that appears.

6)Once you have judged your data to be satisfactory, print copies of your graph of Distance vs Time for each member of your group to include in their lab reports. Don't print out copies of the Data table.

7)If time permits, analyze your distance vs. time graph by fitting a mathematical function to your data using the Logger Pro software. See the figure and instructions on the next page.

Click on Analyze in the menu bar at the top of the screen and choose "Curve Fit or click on the "f(x)=" button on the tool bar just below the menu bar. Choose the equation you wish to fit to your data, and then click "Try Fit" button. The equation that Logger Pro fits to your data will appear in the "y=" text box.

8)When you've printed out enough copies of the graph(s) for you and your group, you can choose to save your data on a floppy disk. Go to the File menu and select Save after inserting your disk. If you don't want to save your data (or after you do save), quit the program by choosing File and Quit.