Learning Objectives Until now, we've been learning about how to describe motion mathematically using kinematics. Now, we'll turn our attention to how forces affect the motion of an object. There are several learning objectives here. The first one is to determine what factors affect the acceleration of an object, and discover the mathematical relation between the acceleration of an object, its mass and the force exerted on it. The second objective is to practice systematically controlling variables when constructing a relation between physical quantities. This activity is based on a lab created by D. Brookes and on the textbook: College Physics (2nd ed.) by Etkina, E, Planinsic, G., and Van Heuvelen, A. Boston: Pearson (2019) v Exploring the air track and turbine-powered glider Watch the video below, then read the following description that will help you understand what you're watching. A turbine (an enclosed fan) is mounted on a glider that slides along an air track. Air flowing from small holes in the track levitates the glider so that it slides almost frictionlessly along the track. When spinning, the turbine pushes air to the left. Notice that there is a camera mounted above the glider on the left side of the screen. This camera shows the view of a small spring holding the glider in place while we use the spring to measure the force that air exerts on the glider as the turbine pushes air to the left. Notice that there is a camera mounted above the glider on the left side of the screen. This camera shows the View of a small spring holding the glider in place while we use the spring to measure the force that air exerts on the glider as the turbine pushes air to the left. Top-view camera 30 -"' ,,.lllll l Turbine-Powered Glider Mass: A Fan Force: 3 120 frames per second, 2x slow motion MASS FAN FORCE \" Top view 0. @000 sec Frame 0 120 fps 1. Watch the video, and try to describe the motion of the glider in words. (Use the default settings: Force 3 and Mass 800 grams). Now select which statements below accurately describe the motion of the glider. Hint: ( There is more than one correct statement.) Select all that apply: The glider travels at roughly constant speed as it moves along the air track, because it covers the same distance in each frame of the video. V The speed of the glider is increasing as it moves along the air track because it covers more and more distance each frame. V The glider is accelerating because its speed is changing as it moves along the air track. The force of the glider is increasing because it goes faster and faster. [ The glider is slowing down because someone catches it at the end. ] v unlimited submissions remaining Score: 2/2 Comments: \\I... __.l. :4.I 2. What could you do to have a more precise description of the motion of the glider? In particular, how would you tell whether its acceleration constant or not? Hint: ( There is more than one correct answer.) Select all that apply: V Collect position and time data from the video. Use that data to plot a graph of position versus time. If the acceleration is constant then $05) = (1:0 -l- vot -l- %at2 and the graph will be parabolic in shape. Measure the position of the glider at random points in time and examine them more carefully. Measure the initial and final positions of the glider and the time it took to travel that distance and divide the distance by the time. Collect position versus time data from the video at regular time intervals, plot a graph of average velocity versus time for each time interval. If the resulting graph is linearly increasing, the acceleration of the glider is constant. Collect position versus time data from the video at regular time intervals, plot a graph of average velocity versus time for each time interval. If the resulting graph is flat, the acceleration of the glider is constant. Collect position and time data from the video. Plot a graph of displacement An: versus time squared (t2 ). If the resulting graph is linearly increasing the acceleration is constant. Part 1: Dina's Data Let's study the data collected by another student named Dina. 1. Student Dina thinks the acceleration might be constant but she isn't sure. She collects data and makes the following .Saved motion graphs: position vs time velocity vs time 80 150 60 100 position (cm) velocity (cm/s) 40 20 50 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 time (s) time (s) Do the graphs make sense to you? Explain how they are consistent with each other. What can Dina conclude about the motion of the glider from these graphs? BIU FEEEv Part 2: Determining the acceleration of the glider In this activity we'll be investigating what affects the acceleration of the glider. Therefore, we need to figure out how to determine the acceleration. We've just figured out that the acceleration of the glider is constant. Is there a way to determine the acceleration without making a motion graph for every video? 1. Let's apply kinematics so we can determine the acceleration of the glider after the ribbon is cut. Notice that you can easily measure the elapsed time starting when the ribbon is cut, and a distance that the glider travels. Describe how you can use these values (a single displacement Am and the time At) to determine the acceleration of the glider. Do a sample calculation for Force 3, Mass 800 grams. Compare your results with other groups Hint: Remember; Am = voAt -l- %0At2 BIDEEE I'l o|l Score: 0/2 You've probably noticed that you can vary the "fan force" in the video. Let's look more closely at the forces exerted on the glider, and how to measure them. 1. Advance the video until the just before the thin ribbon is cut (but after the fan is turned on.) While the fan is on, the spinning turbine blades exert a force on the air to the left. If the turbine is pushing air to the left, which way does the air push on the turbine? . Air exerts a force on the turbine blades to the right ' Earth exerts a downward gravitational force on the glider I The spring exerts a force on the glider to the left ~/ 1 / 2 submissions remaining Score: 1/ 1 Comments: You got it! 2. While the glider sits motionless just before the ribbon is cut, which of the following statements bestdescribes the horizontal forces exerted on the glider by other objects? Hint: What object is pushing/pulling the glider to the right, and what object is pushing/pulling to the left? How are the two forces related? The turbine pushes the air to the left, an equal and opposite force exerted by the air on the turbine pushes the glider to the right. The force of the turbine pushes the glider to the right, while the spring pulls to the left. The turbine force is greater than the spring. The spring pulls the glider to the left, while the air expelled by the turbine pushes the glider to the right. The two forces are equal because the glider is stationary. There are no forces exerted on the glider because it is not moving. v 0/ 3 submissions remaining Score: 1/1 Comments: You got it! 3. Advance the video until the just after the thin ribbon is cut. While the glider is accelerating, which of the following force diagrams correctly shows the forces exerted on the glider by other objects? Ftrack on gl FEon gl Ftrack on gl Fair on gl FE on gl Ftrack on gl Fel on air Fair on gl FE on glScore: 1/1 Comments: You got it! 4. Notice that you can use a ruler to measure the force exerted by the spring on the glider. Now you are going to do a practice measurement. Use the ruler to determine the value of "Fan Force 3" in Newtons. Hint: Think about how to line up the force "ruler" - what is the magnitude of the force exerted by the spring on the glider before the fan is turned on? V 2 / 4 submissions remaining Part 4: Designing Experiments Now we are ready to explore what quantities affect the acceleration of the glider. Notice which quantities you can vary in the video. Think of which are independent and which are dependent variables. 1. With your group, plan what you will do using available videos to figure out how the acceleration of the glider depends mathematically on the forces exerted on it and its mass. Record your ideas in the text box below. B I U E E Go Score: 0/52. In the space below, write the procedure you will use to find the relation. Hint: Make sure you have enough detail that someone else could reconstruct your experiment(s). BIU E Score: 0/53. What are the independent variables in this experiment? (There are multiple correct answers.) Hint: Independent variables are the various factors that will affect the dependent variable if they are changed Select all that apply: ' Acceleration of the glider I V Force exerted on the glider by air J Mass of the glider V unlimited submissions remaining Score: 2/2