Physics for the Inquiring Mind (PHYS 105)                  Spring, 2005 Exercises for Tuesday, March 15. [1] Your groups for the next unit will be as follows: Team Aconcagua: Barrish, Castellano, Lilge, Myers Team Denali: Birth, Burke, Fricke, Hahnebach, Lowery Team Elbrus: Fretz, Kincaid, Laird, McArthur, Stancick Team Everest: Berger, Cook, Hoyt, McClure, Wilson Team Kilimanjaro: Amerman, Arminio, Gress, Miller, Virus Team Kosciuszko: Barnes, Cortese, Melrath, Merline, Rutt [2] Although these will be your groups for the unit, for today we will work in the following Supergroups: American Supergroup:  Aconcagua + Denali Eurasian Supergroup: Elbrus + Everest Afro-Australian Supergroup: Kilimanjaro + Kosciuszko [3] As a supergroup, go to one of the three computers in the lab that has a blue motion sensor next to it.  Turn the computer on if it is not already on. [4] It is often useful in science to represent the motion of an object graphically.  In this activity, you will be exploring the relationship between the motion of an object and the appearance of the graphs representing its motion.  Throughout the course of the activity, you will be studying two different types of graphs:  (1) Position vs. Time, and (2) Velocity vs. Time.  Your primary goals for the activity are to answer the following questions: If the Position vs. Time plot of an object is horizontal, how is it moving? If the Velocity vs. Time plot of an object is horizontal, how is it moving? Why do the answers to questions (a) and (b) differ? The Activity [1] After your computer has booted up, plug in the USB cable from the motion sensor. [2] After you make the connection, a pop-up dialog box should appear on the screen.  Choose Launch EZ-Screen. [3] On your group's computer, you will see a blank graph of position vs. time.  In the lower right hand portion of the screen, near the Score box, you will see buttons corresponding to a few different profiles.  Choose the one that looks like this:      So choosing should cause the profile to appear as an overlay on the graph. [4] On or near the computer there should be a piece of cardboard.  Have one of the group members take this and stand in front of the motion sensor.  The task is to move the cardboard towards and away from the sensor in such a way that it matches the profile chosen above as closely as possible.  As you move the cardboard, the software will display the position of your piece of cardboard on the plot.  When the person with the cardboard is ready, have another group member start the measurement by clicking on the Green Play triangle in the upper left corner of the screen.  After the measurement has been started, you will have a few seconds to adjust your position before the sensor starts taking data.  Note that, during this time, a triangle appears at the left of the graph to show you where you are. [5] After the run has been completed, you will be shown a Score indicating how closely your motion matched that of the profile.  If you need to, you can hit the Green Play triangle to try again.  Keep trying this until each group member has attained a score of at least 90.  Also keep track of the highest score for your group. [6] How must the cardboard be moving in order to make the position vs. time graph horizontal? [7] After everyone has gotten a 90 or better, switch to the profile that looks like: Again, keep trying until everyone gets a 90 or better, and record your group's highest score for this profile. [8] Now close EZ-Screen by clicking on the                           icon in the upper right portion of the screen. Say “no” when asked whether to save the EZ-Screen data. [9] On the desktop, locate the Velocity Matcher 1 icon.  Double click on this to open the program. [10] Now you are seeing a plot of velocity vs. time, and you will attempt to match the red velocity profile by moving the cardboard.  Realize that the sensor is now going to show how fast the cardboard is moving, and not where it is.  Have a fellow groupie hit the Start button near the top of the screen, and attempt to match the red profile. [11] Each group member should try this a few times.  If you would like to remove old runs from the screen (so that things don't get too cluttered), use the Data pulldown near the top of the screen to deselect various runs.  If the run has a check mark next to it, it will be shown.  Remove the check mark to get rid of it. [12] How must the cardboard be moving in order to make the velocity vs. time graph horizontal? [13] Discuss these results within your group, and arrive at an explanation of the difference between the answers to Questions [6] and [12].  After you have done so, carefully write up a single explanation of this difference for your group.