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### Question Description

Physics 185 Virtual Lab Exercise

Week 11: Torque

1. Go to the Phet website: https://phet.colorado.edu/ Click on “subjects,” then “physics.” Find the simulation called “Torque”

a. Make sure you uncheck the option boxes for the “Optional Offers” for various McAfee junkware.

b. Some browsers disable flash from running on pages by default as a security feature. You may need to do a quick google search for “enable flash in [my browser]”.

1. There are four tabs at the top. Pick the one labeled “Moment of inertia.” At the bottom left, check the box for the ruler. At the top left, move the slider (a blue arrow) under “Applied Torque” to about 2.

2. Put the ladybug at edge of the wheel. Use the ruler to find r for the ladybug. Click the “go” button and let it run for 5 seconds, then hit “stop.”

The graph on the bottom left will give you the angular acceleration α. You may have to adjust the scale using the up-and-down arrows to make the line appear. Since α is constant it will be a horizontal graph line. There should also be a legend which gives α exactly.

Reset everything, place the ladybug closer to the center and repeat. Repeat twice more for two more ladybug positions.

For each trial, use τ and α to find the total moment of inertial of the system I. This will be the I of the wheel plus I for the ladybug.

Make a graph with the total I calculated above on the y-axis and r2 on the x-axis, where r is the radius of the ladybug. What is the shape of this graph? Can you use it find the mass of the ladybug? Can you use it to find the I of the wheel? Compare your I for the wheel to what you can calculate using the numbers shown at the left side of the screen, below the wheel. Assume the wheel is a disk.

3. On the left there are sliders that let you control the shape of the wheel. Change the inner radius so it is just barely smaller than the outer radius, effectively making a hoop.

Repeat the above experiment.

4. Repeat, but with the inner radius equal to half the outer radius. Find the formula for a disk with a hole in the middle and use this for comparison.

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