Be sure the Gizmo has these settings: adius 8 m, mass 5 kg, and velocity 8 m/s. Then click Play and observe the motion of the puck. a. The puck in the Gizmo is traveling at a constant speed, but it is NOT traveling at a constant velocity. Explain why. b. Because the velocity of the puck is changing (because its direction is changing), the puck must be experiencing an acceleration. Click BAR CHART and choose Acceleration from the dropdown menu. Check Show numerical values. The leftmost bar shows the magnitude of the acceleration, or lal . The other two bars show the x- and y- components of the acceleration, ax and ay. What is the value of lap Jot this value down, along with radius = 8 m, so that you can refer to it later. c. Keeping velocity set to 8 m/s, set radius to 4 m. (To quickly set a slider to a value, typing the number in the field to the right of the slider and press Enter. ) What is the new magnitude of the acceleration, lap Jot down this new value along, with radius — 4 m, with your previous data. d. Now set the radius to 2 m. What is the resulting value for lap Record these values along with the others. . Examine the corresponding pairs of values for the radius and the magnitude of the acceleration, lal. How does lal change when the radius is divided by 2? How do you think lal changes when the radius is multiplied by 2? Multiplied by 3? f. Choose your own values for the radius to test your answers in the Gizmo. What were your results? You should have found that, in general, when the radius is multiplied by a number, I a I is divided by that same number. Also, when the radius is divided by a number, lal is multiplied by the same number.
One way to say this is, the magnitude of acceleration is inversely proportional to the radius. 2. Click Reset 0. Set radius to 8 m, mass to 5 kg and velocity to 2 m/s. Click Play 0. a. Display the BAR CHART pane and be sure that Acceleration is selected. Check Show numerical values to display the magnitude of the acceleration. What is lap Jot down b. Set velocity to 4 m/s. What is the new value for lap Jot these values down with those you recorded in the previous step. c. Change the velocity one more time, to 8 m/s. What is lal in this case? Record these values as well. . You have doubled the velocity twice. How did lal change each time? e. You should have seen that multiplying the velocity by 2 causes lal to be multiplied by 4. How do you think tripling the velocity affects lap How do you think dividing the elocity by 5 affects lap Choose your own values for the velocity and test this in the Gizmo. f. Explain the relationship, in general, between velocity and the magnitude of acceleration, lal. Use the words "directly proportional" in your answer. Part 2: Force on an Object in Uniform Circular Motion 3. Click Reset.
Set the Gizmo back to the original settings - radius 8 m, mass 5 kg and velocity 8 m/s. Click Play. You saw in the previous activity that the puck is undergoing an acceleration. This means that some force must be acting upon it, and the direction of that force must be the same as the direction of the acceleration. . In the DESCRIPTION pane, select Show velocity and acceleration vectors. The two vectors are shown in the SIMULATION pane - the velocity vector in green and the acceleration vector in blue. Describe the direction of the velocity vector. Describe the direction of the acceleration.
What does the acceleration vector always point toward? b. You should notice that, when the settings of the Gizmo are held constant, the magnitude of acceleration, lal, of an object is constant. (lal is the "length" of the acceleration vector. If you like, you can also go to the BAR CHART pane, with Acceleration selected, o see the value of la I . ) Explain why the acceleration, however, is NOT constant. c. Using the direction of the acceleration as a hint, what object do you think provides the force that keeps the puck traveling on its circular path? . Click Pause 0. If the string were to break at this instant, what path would the puck travel? e. Click the GRAPH tab. Then select Force vs. time from the dropdown menu to display a graph of the x- and y-components of the force that acts on the puck (Fx and Fy). Click Play. When the puck reaches the point in its path closest to the bottom of the screen, click Pause. What is the direction of the acceleration when the puck is at this position? Is Fx positive, negative, or zero? What about Fy?
What does this tell you about the direction of the net force acting on the puck in this position? determine the net force acting on the puck by looking at the magnitude of Fy acting on the object at the point closest to the bottom of the screen. (At that point, Fx = O, so Fy is the entire force. ) a. What is the net force acting on the puck when the mass of the puck is 3 kg? Jot this value down, along with the mass, to refer to later. b. Set the mass of the puck to 6 kg. Then determine the net force acting on the puck n the same way. Record this data.
How does the force compare with that recorded in the preceding step? c. Set the mass to 9 kg and repeat the process one more time. d. What is the relationship, in general, between the mass of an object and the net force that acts on it when acceleration is held constant? Use the words "directly proportional" or "inversely proportional" in your answer. e. Based on this relationship, what would you expect the force to be if you were to set the mass of the puck to 1. 5 kg? Use the Gizmo to check your response. COMPLETE THE 5 ASSESSMENT QUESTIONS LOCATED UNDER THE GIZMO.
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