Relationship to theory: This activity involves the motion of bodies under constant velocity.

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1 UNIFORM MOTION Lab format: this lab is a remote lab activity Relationship to theory: This activity involves the motion of bodies under constant velocity. LEARNING OBJECTIVES Read and understand these instructions BEFORE starting the actual lab procedure and collecting data. Feel free to play around a little bit and explore the capabilities of the equipment before you start the actual procedure (begins on page 8). to determine the relationship between position and for a body moving with constant velocity to apply elementary statistics to experimentally observed data to arrive at the value of the constant velocity of the body to demonstrate graphically and mathematically, from the observed experimental data, the relationship between distance and when velocity is constant. BACKGROUND INFORMATION In this experiment we will investigate motion without acceleration. Motion without acceleration is uniform (constant velocity) motion, which means it describes the motion of an object that has constant speed and constant direction. Accelerated motion is the motion of something with either a changing speed or a changing direction. In the next experiment, we will deal with changing speeds. Our goal is to determine the relationship between the position and for an object moving with a constant velocity. You can do this by simply noting the for the object to reach certain positions. First however you must put an object into constant velocity motion. One way to do this is with a constant velocity motor. Many motor driven toys and model cars work this way. In this experiment however, you will use a non-motorized object. Unfortunately, most non-motorized objects don't move with a constant velocity because they slow down and stop after a relatively short period of. In order to keep an object from slowing down, you must remove friction. Later you will learn that an object moving with no friction and no external forces acting on it will move forever with a constant velocity. To remove friction you will use an air-track which is a linear track that has many holes through which air blows, suspending a sliding sled. The sled moves along on a layer of air and does not actually touch the underlying track. The air-track is a one-dimensional version of the common air-hockey table which has a suspended puck free to move in two dimensions. To start the sled moving, a small rubber band is used to give it a push when you release the sled from the launcher by de-energizing an electromagnet on the launcher. Creative Commons Attribution 3.0 United States License 1

2 The position equation for an object moving with a constant velocity is: D vt where D is the distance traveled, v is the constant velocity, and t is. Since v is constant, this equation represents a proportional relationship between distance traveled and. You will be using the Remote Web-based Science Lab (RWSL) facility In Denver, CO to perform this experiment. It is a real lab that you will access through the Internet using your computer. You will access the experiment through the RWSL Lab Scheduler in your D2L course, and you will communicate with your lab partners and the Lab Technicians using the Mumble software that you installed on your computer during the setup process. EQUIPMENT Paper Pencil/pen Computer (access to remote laboratory) Creative Commons Attribution 3.0 United States License 2

3 PREPARING TO USE THE RWSL Setting up your computer for use with the RWSL: Ensure that your computer system is capable of interacting with the RWSL microscope. Currently RWSL works only on the Microsoft Windows operating system (XP or later) and a relatively up-to-date browser. To confirm that your system meets minimum requirements, visit this website: and follow the steps provided. Scheduling at the RWSL: Go to your online class website in D2L and open the RWSL Scheduler. Select the date and you would like to attend lab. Try to choose a classroom that already has students scheduled in it so you have some lab partners to work with. Before you connect to the RWSL: Open the Mumble software and connect to the Denver NANSLO server. This will establish contact with the Laboratory Technicians in the lab so they can assist you if you have any trouble. Connecting to the RWSL : When it is to attend your scheduled lab, go to your online class website in D2L and open the RWSL Scheduler. There will be a link just above the calendar that allows you to access the lab. NOTE: This link will not be available until the exact that your lab activity starts. Figure 1 - RWSL Scheduler Link to Lab Creative Commons Attribution 3.0 United States License 3

4 INTRODUCTION TO THE REMOTE EQUIPMENT AND INTERFACE: DO NOT BEGIN WORKING ON THE LAB PROCEDURE UNTIL YOU HAVE READ ALL OF THIS INTRODUCTORY SECTION. THE PROCEDURE BEGINS ON PAGE 8. We will be using the RWSL to collect data for this experiment. Here is a quick introduction to the control panel that you will use to control the equipment and to see what is happening in the lab. Take a look at Figures Figure 2 and Figure 3 to see what the control panel looks like. On the left side of the screen are equipment controls, and on the right side is a video window with camera controls. You will use a robot arm and a screw-drive robot to move and position the equipment as necessary. You will notice in Figure 2 that there is an option to put the sled onto the scale to obtain its mass. In this experiment, it is not necessary to know the mass of the sled, so we will not use this function. However, it will be used in some future experiments. Click here to turn on the Air Supply If it is green, Figure 2 - RWSL Interface: Setup Experiment screen Creative Commons Attribution 3.0 United States License 4

5 Click on these arrows to change data tables. There are 10 data tables, Figure 3 - RWSL Interface: Experiment screen In order to determine the distance that the cart has moved for each, you will need to use the cameras to determine the location of each photogate. Camera 1 should be used for the first photogate (Figure 4), camera 2 for the second, and so on. Select each camera and then click preset 2 to zoom in on the photogate and read its location from the center scale on the side of the air track. Before it is launched, the front edge of the sled is located at 21.4 cm from the end of the air track. Creative Commons Attribution 3.0 United States License 5

6 Shows the location of photogate #1 Figure 4 - Camera 1, preset #2, showing the location of Photogate #1 NOTE: HAVE SOME FUN! Before you begin the data collection phase of the experiment, investigate the capabilities of the equipment a little bit first. Look around with the cameras and make sure you understand what you are seeing, as well as what each of the camera Creative Commons Attribution 3.0 United States License 6

7 presets are showing you. As long as you are careful, there is nothing wrong with "playing around" with the equipment a bit just to figure it out. Creative Commons Attribution 3.0 United States License 7

8 EXPERIMENTAL PROCEDURE: (REFERENCE THE ABOVE SECTIONS FOR DETAILS) 1. Log into Mumble and establish communication with the Lab Technician. 2. Using the link in the RWSL Scheduler on your course webpage, access the RWSL and take control of the interface. Data Collection: The approach to the determination of the value of the constant velocity of the sled will be to generate a statistically significant set of data, and calculate the mean, the median and the mode of the sample distribution. A total of ten "runs" will be made in which four discrete points in the linear path will be recorded. A ten by four matrix of data will be recorded. The and distance data will be analyzed to determine the relationship between distance and under these conditions. Data Observations: Refer to Fig. 2: RWSL Interface. Incremental Time Values The timing data display consists of the eight numerical windows labeled "photo gate 1, 2, 3, 4". The first display is the value in seconds that has elapsed since the sled was launched and the leading edge coincides with the prepositioned photo gate. The second window is the in seconds that has elapsed since the leading edge of the sled initiated the signal and the trailing edge interrupted the signal. Thus the remaining three blocks of data provide the additional timing profile of the arrival of the sled at each of the designated points. Refer to Figure 3: Camera 1 Preset 2 showing the location of photo gate #1 Incremental Distance Values There are two distance values that will be useful in this experiment: the distance the sled has travelled from the it has left the launcher, and the distance it travels as it passes through each photogate. The location of each photogate is observed on the scale as described In the Figure 3 guidelines. The leading edge of the sled is located 21.4 cm from the end of the track when it is on the launcher. The student will use the prepositioned cameras to read the measuring tape value which gives the location of the corresponding photo gates. See Figure 3 for an actual example of the expected video frame. The distance travelled by the sled as it passes through each photogate is equal to its total length, which is 14.1 cm. Creative Commons Attribution 3.0 United States License 8

9 Procedure: All operations are "mouse" controlled with cursor and right/left click as required-indicated. "Select", "Initiate" and similar commands involve placing the cursor over the indicated label, control or display and executing the command by normal click. Section1: Data Generation. This section will configure the air track for operation, load the sled on the track, travel along the path and generate the /distance data. This section will configure the air track for operation, load the sled on the track, travel along the path and generate the /distance data. ( ) Connect to the Mumble Server and establish communication with the Lab Technicians. ( ) Connect to the Remote Lab through the RWSL Lab Scheduler in D2L. After the Remote Lab window has opened, close the D2L window before proceeding. ( ) Assure no error messages are displayed on your computer screen. (This will confirm that a stable link with the RWSL server has been established and we are good to go for operation.) Ask the Lab Technicians if you have any issues or questions. ( ) From the SETUP EXPERIMENT panel (Ref. Figure 1) ( ) Select Move Sled to Track This places the sled onto the air track and energizes the launcher so it engages the sled. ( ) Select the RUN EXPERIMENT panel (Reference Fig. 2-RWSL Interface) ( ) Increment TRIAL NUMBER counter, if necessary, to get an empty data table ( ) Pan area coverage camera, verify sled is in place and no obstacles are impacting the sled track ( ) Select Preset 2 for each camera to view the respective photo gate positions Gate 1 cm, Gate 3 cm, Gate 2 cm Gate 4 cm Creative Commons Attribution 3.0 United States License 9

10 ( ) Select RUN EXPERIMENT (Reference Fig. 2-RWSL Interface) Select LAUNCH SLED ( ) Pan the cameras as necessary to visually verify sled travels freely down the air track with a smooth motion. (NOTE: depending on your Internet connection speed, the streaming video feed can somes make the motion appear inconstant. However, you can confirm the smoothness of the motion from the timing data that you will collect below.) ( ) From photo gate display panel record the values in DATA TABLE #1 ( ) Recapture the sled onto the launcher and collect another set of data. ( ) Click the button labeled "Energize Launcher". ( ) Go to the Setup Experiment tab (Figure 1). ( ) Using the raise/lower controls, level the track ( ) Select the 1 cm button on the left side of the screen and click the down arrow to lower the left end of the track by 1 cm. The sled will move back down the track and will stick to the electromagnet, holding it in place. ( ) Return the track to a level position as it was in the first run ( ) Go back to the Experiment tab (Figure 2) and make sure you have an empty data table. ( ) Click "Launch Sled" to release it from the electromagnet. Wait for the data table to populate with values. Complete a total of ten runs as per the preceding procedure. Populate Data table #1 from these data. Section 2 -Data Capture and Reduction A total of ten runs will comprise the data set for this experiment. Data table #1 will be populated with the discrete distance/ data generated by the successive runs. The mean and Standard deviation will be computed from this data. The distance measurements will be considered discrete and in the middle of the tolerance. The ten "run" values of for each of the four distance points will be analyzed with the mean and standard deviation calculated. ( ) Populate Data Table #1 from the ten separate runs Data Table #1 (Raw Data) Creative Commons Attribution 3.0 United States License 10

11 PHYSICS SEMESTER ONE Time 10 Enter Photogate 1 Exit Photogate 1 Enter Photogate 2 Exit Photogate 2 Enter Photogate 3 Exit Photogate 3 Enter Photogate 4 Exit Photogate 4 ( ) Use the entry/exit s from each photogate along with the length of the sled (14.1 cm) to calculate the average instantaneous velocity at each photogate. Also, use Excel to calculate the standard deviation of the it takes the sled to get through each photogate. ( ) Make a scatter plot of the average velocity at each photogate (y-axis) vs. the average entry at that photogate (x-axis) ( ) Insert a linear Trendline and display the equation and the R 2 value. ( ) Record the equation and R 2 value here:. ( ) Compute the value of the constant velocity of the sled by determining the slope of the plot ( ) Reduce the photogate position data by subtracting 21.4 cm from each one (to adjust for the fact that the front of the sled is not at zero cm) D1 r = D2 r = D3 r = D4 r = Creative Commons Attribution 3.0 United States License 11

12 ( ) Calculate the average the sled took to enter each photogate. ( ) Using EXCEL, plot the reduced photogate position data from vs. the average photogate entry s from Think about what this plot represents. What do you observe? Fit an appropriate trendline to the data. ( ) Record the equation and R 2 value for the Trendline that fits best here: Section 3-Analysis and Conclusions ( ) What are possible and reasonable sources of error in the data? ( ) If more than ten runs were made, would the true average value be better ascertained? Give the rationale for you re answer. ( ) Can each run be viewed as an independent event? If so what are the implications? ( ) Compare the results from portions and Are they the same or different? What was your expectation? ( ) What was the velocity of the sled as it moved down the air track? Was this velocity truly constant? How do you know? What evidence do you have to support your conclusion? Creative Commons Attribution 3.0 United States License 12