Before you begin your lab activities today, your instructor will review the following: Lab sign-in sheet Lab partners (you will probably work with the same group as during lab #01) Comments on lab #01 Task #1 - Exploring the use of a new measuring tool The "motion sensor" During this semester, you will use the computer at your workstation as many different kinds of scientific tools - from data collection, to data analysis, to data presentation. These computer-based activities are designed to help you study physics concepts as well as to gain experience working with computer technology, including understanding its strengths and its limitations. Each computer has an interface box (small black box) connected to it which allows you to plug in sensors. These sensors are able to measure physical quantities (such as force, light intensity, and sound intensity) and then send those measurements to the computer through the interface box. Using sensors to collect data through a computer interface is often called Microcomputer-based Laboratory, or MBL for short. Equipment: File: MBL Motion; Motion sensor II; Tripod support stand; Large piece of cardboard; Meterstick Turn on the computer and the interface box (switch in the back). Start the DataStudio software by double-clicking on the DataStudio file on the desktop. Open the file MBL Motion by double clicking on the icon called MBL Motion inside the Physics 141 folder. You should now be looking at a window containing the following tool bars and graph: Start/Stop collecting data button Time since data collection started 2004 - UNL page 1 of 7
Graph of position data as a function of elapsed time. Graph of velocity data as a function of elapsed time. Start collecting data by pressing the Start button. Move the piece of cardboard towards and away from the front of the motion sensor. The software has been setup to stop collecting data after 10 s has elapsed. You can also stop data collection by clicking on the Stop button. Now you have the basics for using this software and sensor. In order to give you practice with this tool (which you will be using a lot today and in many future labs!), please complete the following mini-experiments. Record the following information for each mini-experiment in your logbook: Summarize your result or conclusion Describe your evidence for this conclusion Mini-experiment #1 - How can you use the "Zoom Select" button to exam a specific region of your data? Mini-experiment #2 - What can you do with the "Smart Tool" button? Example of using the Smart Tool: DataStudio Tip: You can click on the "Scale to fit" button to have the software automatically adjust the scales of the graph so that all of the data is displayed. 2004 - UNL page 2 of 7
Mini-experiment #3 - Devise a way to measure the length of one person's arm using the motion sensor. Hint: You may want to use a piece of cardboard to help with this mini-experiment. Print a copy of your evidence for each member of your group. To do this: click on the graph once with the mouse to select the graph select Print from the File menu. Affix a copy into your logbook (using tape or staples). 1. Compare the arm length you obtain with the MBL equipment to what you measure using a meterstick. How well do they compare? Calculate a percent difference between the two values as described in Reference C. Quit the MBL Motion file by selecting Quit under the File menu. Task #2 - Using the motion sensor to study motion - Graph Matching Open the file Match-Graph #1. Set up the motion sensor so that you can stand up and walk back and forth in front of it. You will want to be able to walk from being very close to the sensor (say within 0.5 m) to far away (say 2 m away). Discuss with your partners (before trying to move!) how you think the person should move to match the displayed graph. Also discuss your prediction of what the shape of the velocity graph will look like. Using your body as the moving object, walk back and forth in front of the motion sensor. Be sure to collect data as you move. Repeat the experiment over and over until you have made a good clean match to the displayed data. It doesn't have to be a perfect match, but it should be close! Once the graph has been successfully matched, complete the following items based on your data: 2a. Make a record of the matched graph in your logbook: If you are the person who actually moved: Print one copy of the resulting graphs and include the printout in your logbook. Identify it as "Match Graph #." Be sure that you have appropriate labels for the axes of the graphs. 2004 - UNL page 3 of 7
If you are not the person who actually moved: Make a careful sketch of the graphed position and velocity data in your logbook. Be sure that you have appropriate labels for the axes of the graphs. Give the name of the person who did the moving. 2b. Using words, describe in detail how the person moved to create the specific graph shape. Include information like the direction of movement and how fast the person was moving. Your description should refer to all important intervals on the graph. Graph Matching #2 - #3 Repeat this procedure for Match-Graph #2 and #3. You must take turns being the moving object so that each person in your group has at least one printed graph of their motion. For each of these files (#2-#3), every person should record answers to items 2a and 2b, as listed above. 2004 - UNL page 4 of 7
Data Analysis of the Graphs You have now collected three sets of graphical models of human motion. Use the graphs of your motion to answer the following questions. Be sure to cite specific examples as evidence when answering each question. 3. (a) Give an example that represents the motion when someone didn't move at all. Sketch and describe the shape of that part of the position graph. (b) (c) Give an example that represents the motion when someone moved the slowest (but was still moving). Sketch and describe the shape of that part of the position graph. Give an example that represents the motion when someone moved the fastest. Sketch and describe the shape of that part of the position graph. 4. How is the steepness of the slope on a position graph related to the speed of the motion? 5. How would you need to move to produce a negative velocity? To produce a positive velocity? To produce a zero velocity? Task #3 - Use the motion sensor to study your natural walking gait Quit the Match-Graph file and open the MBL Motion file you were using previously. Have one person start at least five steps away from the motion sensor. He/she should walk towards the sensor as naturally as he/she can, stop for an instant, and walk backward away from the sensor. Look at the velocity versus time data for the walk. {If the data is not good, do the forward and backward walk over again. It only takes a few seconds to collect another set of data.} When you are satisfied wit h the data, adjust the graph axes to best display the data. Print copies of the resulting graphs for each person in your group. Be sure to affix it to your logbook (using tape or staples) so it won't fall out and be lost. Give the graph a meaningful title that explains what motion is represented and who was moving. 2004 - UNL page 5 of 7
Use the graphed walking data to answer the following questions. 6. Describe in words what the position and velocity graphs are telling you about your motion. Give as much detail as you can. 7. Even though the velocity lines are basically straight, do they have a little "wiggle" in them? Compare and contrast with other people and other groups. Do all groups have this? 8. What does the "wiggle" mean in terms of change in velocity? (a) Identify on your graph where in the wiggle are you speeding up and slowing down. (b) Where in your gait could you be speeding up or slowing down? Examine the push off and heel strike portions of your gait. (c) Determine your stride length from your data. How did you do this determination? Does this value seem reasonable? Explain. 9. (a) From your graphed data, estimate your average walking speed. (b) Write a functional model that represents your walking (displacement vs. time). Explain why you think this model is appropriate. End of Lab Procedures! Don't forget to write your Implications discussion. Turn your work in to your lab instructor before you leave. Quit the Data Studio software program by selecting "Quit" under the "File" menu. If this is the last lab section of the day, then "Shut down" your computer and turn the power off to the interface box. Want More Information? Position, Distance, and Displacement (see Walker, Section 2-1) Speed and velocity (see Walker, Sections 2-2 & 2-3) 2004 - UNL page 6 of 7
Graphical Models (see Reference A and Walker, Sections 2-2 & 2-3) Percent difference (see Reference C) Using the DataStudio software (see Reference D) 2004 - UNL page 7 of 7