Mahela Plasencia Torque Web Quest

Physics Web Quest: Torque Name Mahela Plasencia Period 2 Open the Physics Animations Folder Open torque ( http://phet.colorado.edu/simulations/sims.php?sim=Torque ) Part I: Torque 1. Click the tab at the top that says torque 2. Set the force equal to 1 N. 3. Click Go let this run for at least 10 seconds 4. What is the torque on the wheel (include direction). Torque= 4N-m in perpendicular direction. 5. What eventually happens to the ladybug? it flies off to the turntable . 6. From Newton’s second law, a force will cause an acceleration . 7. When considering angular motion, a torque will cause an angular acceleration (consider both torque equations) 8. What must be the centripetal force that keeps the ladybug moving in a circle? friction 9. Why does this force eventually fail? Because of the existence of constant value of static friction. 10. Reset all, and set the force back to 1 N. 11. Observe the acceleration vector as you start. Describe how it changes. The acceleration grows rapidly and starts to grow towards the center. 12. Will the acceleration vector ever point directly to the center? No Why / Why not? (The next steps might help you answer this question) This is because there is a tangential component which is the net torque on the system. 13. Reset all. Set the force back to 1 N. 14. Hit start, wait about 2 seconds, and set the brake force to 1 N. Hit enter and observe. 15. Describe the motion of the wheel: It is moving with a constant angular velocity . 16. What happened to the acceleration vector? Why? The tangential component is absent when the torque is counter with an equal force . 17. What is the net torque? The sum of the individual torques. 18. Reset all. Set the Force back to 1 N. Hit Start. 19. After a few seconds, set the brake force equal to 3N and hit enter. 20. Right after you set the break force, calculate the net torque (check with the graph):

21. Eventually the disc stops, and the net torque is zero. This is because the breaking torque changed as you can see in the graph. Why did it change? The braking force creates a resistance to motion due to friction. It therefore does not affect the direction of motion of the torque but overpowers it when the break is applied. Part II: Moment of Inertia 1. Click the Moment of Inertia Tab at the top. 2. Disregard any millimeter units. They should all be meters. 3. To best see the graphs, set the scale of the torque graph to show a range of 20 to -20. 4. Set the Moment of Inertia Graph to show a range of 2 kg m 2 to – 2 kg m 2 5. Set the angular acceleration graph to show 1,000 degrees / s 2 to –1000 degrees / s 2 6. Calculate the moment of Inertia for the disk with the given information. I=MR^2=0.12 x 4^2=1.92 7. Hold the mouse over the disk so the mouse finger is pointing anywhere between the green and pink circles. 8. Hold down the left mouse button. Move your mouse to apply a force. 9. Look at the graph and try to apply a force that creates a torque of 10. 10. Use the ruler to determine the radius at any point between the green and pink circles. r = 2.80 m 11. Calculate what the applied force must have been. Angular acceleration = r x F 10= 3 x F F = 3.3N 12. Calculate the angular acceleration of the disk. Work in SI units, and then convert to degrees / s 2 . Compare to the graph to check your answer. 10= (.96) (2). 2=10.42. rad/52 x 180/rad = 597/s^2 13. Predict what will happen to the moment of inertia if you keep the mass of the platform the same, but you create a hole in the middle (increase inner radius). Increase-> mass is farther from center, r^2 I=Sr^2dm 14. Set the inner radius equal to 2. Calculate the moment of inertia for this shape. Set the disk in motion and check your answer by looking at the moment of inertia graph. I = 1/2m (r1^2 + r2^2) I = ½ (.12) (2^2 +4^2) I= 1.2 kg m^2