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Center of Mass

Part I. You are provided with a cardboard version of the polygon shown. Locate the center of mass of the polygon experimentally. Write a brief description of what you did.

Part II Drag the program P110CenterOfMass1.ip to MyDocuments and open it. It contains two objects, a small ball, and the polygon, on which a point is indicated with a small dot ("Initial Point" on sketch). These are thrown in the air near the earth.

1. Run the simulation and sketch the paths of the circle and the point on the polygon. How would you describe the two paths? Which path looks simpler?

2. Now drag the point on the polygon to the second location indicated above and run the simulation. Sketch the paths of the circle and the point on the polygon. How have the paths changed from before? Which is simpler?

3. Can you find a location for the point that provides similar paths for the ball and the polygon? If so, mark it on the drawing of the polygon above. How does it compare with the center-of-mass location that you found experimentally?

Part III Drag the program P110CenterOfMass2.ip to MyDocuments and open it. It shows a green circle, a red square, and a blue arc that are thrown with different speeds. There are also two markers on the screen.

1. Run the simulation and sketch the trajectories of the three objects.

2. Show the Center Of Mass of the system: Under the View menu pick Show System Center of Mass. It will not appear until the simulation is run.Run the simulation and sketch the path of the center-of-mass.

3. Now drag the circle so that it is just to the right of the other marker, and run the simulation. Now there should be a collision. Sketch the trajectories of the objects and of the system center of mass. Describe in words the motion of each object.

4. Write a statement that describes the usefulness of the center of mass.