Motion the Easy Way
Physics of the Mundane
Adam Johnston
Special note: Meeting place will be in SL 221 (physics laboratory) for these labs.
In our previous analysis of motion, every data point was recorded by hand, meticulously organized within a data table and finally translated to a graph. This analysis is tedious, and if there were any way to automate the process, you surely would.
This is your lucky day.
This lab is equipped with motion detectors that can be connected to computers. A motion detector collects data and sends it to a computer, where it is immediately organized and presented as a graph. Thus, you can experience and analyze motion simultaneously.
You should fulfill your internal desire to play with the equipment. There are just a few things that are necessary to get you started:
1. Turn the computer Aon.@ To do this, flip the large switch on the wall, next to your computer. A red light should turn on. Then, press the button that has a triangle on it B it should be located on the upper-right-hand portion of the keyboard. Your computer should make a happy noise and then begin to load all of its necessary components.
2. Turn on the AULI.@ This is the interface that allows the motion sensor and computer to talk with one another. It is a small box with several Aports@ in it, sitting somewhere next to the computer. Make sure that it is plugged in to the electrical outlet, and then flip the red switch in the back from A0@ to A1@. Your motion detector (a small blue box) has a cord on it that should be plugged into APORT 2@ of the ULI.
3. Open the motion detector program. Once the hamsters inside the computer have finished turning numerous wheels and gears, you should see various icons on the computer screen. With the mouse, point the cursor to the icon labeled AMotion Detector,@ and double-click it with the mouse button. This useful program will then load within the next few seconds.
Once you are in AMotion Detector,@ there are many things that can be done:
C Click on the AStart@ button. The motion detector will begin to collect data, monitoring the first thing it Asees@ in front of it. The computer should be recording a graph of position versus time. Clicking AStart@ again will repeat the process, overwriting your previous graph.
C You can change the scale of any graph by clicking on a number representing time or distance. For example, if you click on the A10@ on the time axis, you can change it to A30@ so that you can run your experiment for 30 seconds instead of 10 seconds.
C You can change the display. Clicking on the ADisplay@ menu item gives you a list of options. The Aautoscale@ option makes all of the data fit neatly onto your graph. The AGraph Layout@ option allows you to organize multiple graphs, in case you would like to watch your own velocity or acceleration at the same time as your position. (We haven=t described what this Aacceleration@ thing is, but you might be able to analyze it and figure it out on your own.)
C You can temporarily save data. Click on the AData@ menu, and then AData A -> Data B@. This will move your last recorded data to a non-volatile place in memory. Then, you can collect new data on the same graph as the old data. This is very useful when you wish to compare two sets of data.
C You can print a graph. Clicking on the AFile@ menu gives you a print option. Printing your graph may be much less tiresome than sketching it by hand, but please don=t overuse the printer. From the AFile@ menu, you also have the option to quit the program.
Don=t be afraid to play around with the computer and motion sensor. Aside from hurling hardware across the room or rolling bowling balls into monitors, there isn=t much harm that can be done. Also, you should be able to print out your graphs on the laboratory printer. This could supplement your comments in the notebook.
Investigations and questions:
The most obvious moving object to study is probably a lab partner. Standing in front of the motion detector, analyze the motion of someone walking, running and/or standing in front of the detector.
C Which direction to you have to be walking to create positive (upward) slopes on the graph? Why?
C Examine the relationship between the slope of your graphs and the rate at which motion is occurring.
C Examine and explain what happens if you move the motion detector towards and away from a fixed object, such as a wall.
C Test your understanding of motion by trying to fit your own motion to a pre-made graph. Next to the AMotion Detector@ icon should also be icons named ADistance Match File@ and AVelocity Match File.@ Try to match your motion graphs with these. Describe any difficulties with this process.
C By playing with the display menu, you can also show graphs of your velocity. Explain the relationship between your position versus time graph and your velocity versus time graph. (This will require quite a bit of investigation, analysis and thought.) You might consider details such as how to make positive or negative velocities, if (and/or how) you can have large distances and small velocities (or vice-a-versa), what the velocity graph looks like while you=re standing still, etc.
Optional investigations and questions (time permitting, or if you want to come back some other time):
You may also chart the motion of inanimate objects, such as a mass that hangs from a spring.
C Describe the relationship between the position, velocity and acceleration of a mass on a spring. (Again, this requires a fair amount of work and analysis.) Closely examine when position, velocity and acceleration are at their greatest and smallest values. Explain how you can see this occurring when you watch the bobbing of the mass.
C Determine the relationship between mass and period (time) of the motion. You might also try to determine the relationship between the amplitude (size of the motion) and period of the bobbing mass. (Don=t be afraid to construct graphs that show these relationships!)