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b nJV@(Physics Web Quest: Torque Name_________________________
Open the Physics Animations Folder
Open torque ( HYPERLINK "http://phet.colorado.edu/simulations/sims.php?sim=Torque"http://phet.colorado.edu/simulations/sims.php?sim=Torque )
Part I: Torque
Click the tab at the top that says torque
Set the force equal to 1 N.
Click Go let this run for at least 10 seconds
What is the torque on the wheel (include direction).
What eventually happens to the lady bug? _______________________________
From Newton s second law, a force will cause an __________________________
When considering angular motion, a torque will cause an ___________________ ____________________
What must be the centripetal force that keeps the lady bug moving in a circle? __________________________________________________________________
Why does this force eventually fail? ____________________________________ __________________________________________________________________
Reset all, and set the force back to 1 N.
Observe the acceleration vector as you start. Describe how it changes. _________ __________________________________________________________________
Will the acceleration vector ever point directly to the center? ________ Why / Why not? (the next steps might help you answer this question) _______________ __________________________________________________________________
Reset all. Set the force back to 1 N.
Hit start, wait about 2 seconds, and set the brake force (under the animation) to 1 N. Hit enter and observe.
Describe the motion of the wheel: ______________________________________
What happened to the acceleration vector? __________________________ Why? __________________________________________________________________ __________________________________________________________________
What is the net torque? _________
Reset all. Set the Force back to 1 N. Hit Start.
After a few seconds, set the brake force equal to 3N and hit enter.
Right after you set the break force, calculate the net torque (check with the graph) (NOTE: We can add torques like we add forces. Instead of pointing in +/- x/y directions, the torques point in Counter-ClockWise (CCW) and ClockWise (CW) directions):
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 following section covers material we will discuss on Monday. I have included necessary equations. These exercises are good exposure to the concept of Moment of Inertia, and hopefully will help to increase your understanding before we discuss it in class.
Part II: Moment of Inertia
Click the Moment of Inertia Tab at the top.
Disregard any millimeter units. They should all be meters.
To best see the graphs, set the scale of the torque graph to show a range of 20 to -20.
Set the Moment of Inertia Graph to show a range of 2 kg m2 to 2 kg m2
Set the angular acceleration graph to show 1,000 degrees / s2 to 1000 degrees / s2
Calculate the moment of Inertia for the disk with the given information. (Moment of Inertia for a disk: INCLUDEPICTURE "http://frank.mtsu.edu/~phys2010/17_03.gif" \d where M is mass of the disk and R is radius of the disk)
Hold the mouse over the disk so the mouse finger is pointing anywhere between the blue and pink circles.
Hold down the left mouse button. Move your mouse to apply a force.
Look at the graph and try to apply a force that creates a torque of 10.
Use the ruler to determine the radius at any point between the blue and pink circles. r = ___________m
Calculate what the applied force must have been.
Calculate the angular acceleration of the disk. (NOTE: INCLUDEPICTURE "http://frank.mtsu.edu/~phys2010/Lectures/Part_4__L18_-_L23/Lecture_16/Newton_s_2nd/17_11.gif" \d Work in SI units, and then convert to degrees / s2. Compare to the graph to check your answer.
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). __________________________________________________________________
Set the inner radius equal to 2. Set the disk in motion and check your answer by looking at the moment of inertia graph.
Even when the force on the platform changes, the moment of inertia graph remains constant. Why? _____________________________________________ __________________________________________________________________
Fill in the blanks: When the mass of an object increases, the moment of inertia ________________. When the distance of the mass from the axis of rotation increases, the moment of inertia ___________________.
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