Physics 131 Introductory Lab (Lab 0)

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Physics 131 Introductory Lab (Lab 0):

Introduction to Data Studio

OBJECTIVES

m  To familiarize yourself with Data Studio software, including its analysis functions.

m  To familiarize yourself with motion detector hardware.

m  To explore how simple motions are represented on a displacement-time graph.

Note: This lab is just to allow you to familiarize yourselves with the functionality of DataStudio. Some of the activities will be repeated in next week’s lab when we try to get some physics out of them.

INTRODUCTION: SOFTWARE

The Physics lab facilities are equipped with Macintosh G3 computers for data entry and analysis. These computers are networked and will print to printers in the lab, but will not connect to the internet. These computers and the data-collection interface will be the primary lab instruments during the labs this semester.

Your primary software tool for your labs this semester will be Data Studio. Double-click on the Data Studio icon on the desktop to open it. Select “Create Experiment.” You should get a screen like this:

If the last Data Studio user did not clear her or his data, you can do so by clicking on “File” at the top of the screen and selecting “New Experiment” or “New Activity”.

INTRODUCTION: SENSORS

You will use several kinds of sensors to collect data, all of which are designed to interface with the computer through the PASCO PASport. Your experiment today uses a motion sensor. If the sensor is plugged in, unplug it, wait a second, then plug it back into the PASport interface (make sure the pins are aligned properly!) so that a graph for Position data appears. If this doesn’t work, you may have to select “Setup” and then “Add Sensor” and select the appropriate sensor. The “Setup” menu can also be used to change the parameters of the sensors. We’ll experiment with that shortly.

The DataStudio window is split into three areas. The box in the upper left shows which sensors are active. If there is a yellow exclamation point next to one of them, there is a problem, and you should get the TA/professor to help. Once data is taken, the different data runs for each sensor are also displayed here. The second area, in the lower left, shows which DataStudio functions are available. We will use “Graph” almost exclusively. (Under “Graph”, you should see “Graph 1” if there is a graphical window present.) Some of the other functions can come in handy at various times, especially something like “Table” if you want to see the numerical values of the data.

The system should now be ready for a test drive.

INVESTIGATION 1: DISPLACEMENT-TIME GRAPHS OF YOUR MOTION

This first activity explores the working of the Motion Sensor, which will be our primary tool for the first 4 labs in this course.

In order to understand the motion of an object, we have to describe where it is at any given time. So, a plot of an object’s position is the most basic “picture” we can draw in physics. In this activity, we will be making a displacement-time graph using our data. We will measure the physical separation between our detector, which we define as the origin for measurement purposes, and the object, in this case your body.

You will need the following materials:

m  motion detector hooked up to your lab workstation

Activity 1-1: Making Displacement-time Graphs

1.  Open Data Studio and make sure that your motion detector is connected and that the computer recognizes it. You should have already done this in the Introduction, above. If there is any data that was not cleared from the previous user, select File > New Activity, or you can also “Delete All Data Runs” from the “Experiment” menu.

2.  If a graph labeled “Position” is not already displayed, find “Position (m)” under Data on the left side of the screen and click and drag it to “Graph” in the menu on the lower left. You can use this to plot any of the variables from any sensor that you have available.

3.  Check that the beam on the motion sensor is configured properly. For this experiment, since the target of the detector is you, the little switch on the top of the sensor should be set to the “person” setting, not the “cart” setting you will be using in the future.

4.  Prepare to take data! One of you should stand holding a notebook or a textbook as a reflecting surface for the motion sensor. To start recording data, click Start. This button will turn into a Stop button when data is being recorded. You should hear the sensor begin to click, which means it is sending out sounds and listening for the echo which it uses to figure out where you are. The “target” should walk backwards and forwards for about 5 seconds so you get some idea of how the position shows up on the graph.

Now, we’ll use some of the basic features of DataStudio so that you will know how they function in the weeks to come. The first set of these has to do with how your data is displayed, and how the graphs look.

5.  First, note that you can change the scale on both axes by moving the mouse to the numbers and clicking and dragging. When you are going to scale the axes by sliding, the cursor turns into a little icon with arrows at both ends and a squiggle in the middle : .You can also click on the axes away from any numbers to move the graph around in the window. You get a “hand” icon when you have correctly positioned the cursor to move the graph.

6.  If scaling the axes with the mouse is too clunky for you, the left-most button on the “Graph” window is an autoscale, which automatically resizes the graph to surround your data. Try playing with it to see how it works. Also, try selecting a subset of the data by clicking in the graph window and dragging the mouse, then hitting the autoscale.

7.  You can delete individual points by selecting them with the mouse and just hitting delete on the computer keyboard.

8.  You can erase data one run at a time by selecting Experiment > Delete Last Data Run. (You can also Delete All Data Runs, so be careful.) Go ahead, delete a run, then take more data. If the “edited” data won’t go away, you can click on the “Data” button and de-select it.

9.  Take a second data run, and then a third, so that you can see what they look like plotted on top of one another. (If no data shows up on the graph, click on the data run you want to display in the upper left menu and drag it onto the graph.) By clicking on the “Data” button in the “Graph” window, you can select which of the data runs you display on the graph.

10.  Experiment with creating different graphs by dragging one of the datasets in the upper left sensor menu down to the Graph icon on the lower left. You should get a new graph with just that data in it. You can drag another dataset onto the new graph, and it will display there as well.

The next set of features allows you to get at some of the data behind the plots.

11.  Display a single set of position-time data.

12.  With the mouse, select a set of data which reasonably approximates a straight line. To do this, click away from a single point and drag the mouse. A box should appear – drag it along until the points you want to select are in the box. The selected points should turn yellow.

13.  Click on the “Fit” button in the Graph window. You should get a menu that looks like this:

14.  Select “Linear”, as shown. You should get a drawing of a line through the points you selected, plus a little box showing the fit parameters. This is a good way to extract numerical results from the data. You can change the format of the fit parameters by clicking on the box that contains them.

15.  Next, click on the “Smart Tool” button, which is two to the left of the Fit button and looks like this:

16.  By clicking on the center of it and dragging it around, position the Smart Tool over any of the points in your graph. It should give you back the position and time for that point. This is a useful tool for reading off data values. Once you have the tool positioned, you can click on any of the “corners” and stretch it out to get relative displacements from the data point you have selected to anywhere else on the graph. Give it a try…

PRINTING

To print out a graph, click on it so that it is the topmost window in Data Studio, then select “Print” in the “File” menu. The computer will print what is shown in the window, so adjust your axes (by clicking and dragging the numbers) before you print. You can also click on the axes themselves and drag the entire graph around the window.

1.  Print out a copy of your graph with the fit parameters, and a point selected with the Smart Tool. Staple it to the back of this report and keep it for reference.

Activity 1-2: Adding Other Data

2.  Clear the data from your previous experiments. Under the “Display” menu on the top menu bar, you can de-select “Fit” and “Measure” to make the fit box and the Smart Tool go away.

3.  Take one set of clean data (delete points if you need to) with the person moving smoothly away from the motion detector. Again, if no data is displayed, you can click and drag the data set from the upper left menu onto the graph.

4.  Now, under “Setup”, you will find the information for the Motion Sensor. It measures position, but it can calculate velocity and acceleration. Click the radio buttons to select velocity and acceleration, and exit the Setup menu by just clicking on the box in the upper left of its window to close it. The data for velocity and acceleration should now appear in the list of data in the upper left portion of the DataStudio window.

5.  Click on the image of the velocity data in the menu on the upper left and drag it onto the plot of “Position” you should already have. Do the same for the acceleration data. Notice what you get. Also, notice how crummy the acceleration graph looks (You may have to zoom in on it to see just how bad it is if it comes up with some huge scale. Practice using the axes stretching or the Mouse Select/autoscale features to zoom in). Basically, the motion sensor calculates velocity and acceleration by taking the differences x2-x1 and dividing by the time for one tick to get velocity, then doing the same for acceleration. Given the inherent error on the measurements, the second set of differences used to calculate acceleration can have a lot of noise.

6.  You can graph each of the variables separately if you drag them down to the “Graph” icon in the lower left portion instead of adding them to the original graph.

7.  Select the multi-variable graph (the one with position, velocity, and acceleration) and print it for your records.

Activity 1-3: Changing Sensor Parameters

1.  Clear the data from your previous experiments.

2.  Click on “Setup” again.

3.  For the Motion Sensor, you can change how rapidly it acquires data. Click on the “+” to raise the rate up to 50Hz. Exit Setup by clicking on the box in the upper left corner.

4.  Take one round of data with the motion sensor running much faster. You might want to try running away from the sensor. Try it once at high sensor rate, and once at a slow rate to see the difference on the plots. Zoom in to see the differences in detail. Higher data rates will be used in some of the experiments to reveal features of the data that occur at high speed (such as forces in a collision) or to provide better accuracy.

End-of-lab Checklist:

m  Please Quit from “DataStudio” before leaving the lab.

m  Keep your graphs and this writeup for reference.