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course Phy 201
Gold BallHow can we tell that there’s not a gold ball of diameter 1000 meters, just under the ground below the physics lab?
Look up the density of gold, then figure out how much gravitational force that ball would exert on a 1 kg mass in the lab.
The density of gold is 13g/cm^3, and the grav force that that ball would exert is 1.7*10^-3N.
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Assuming that the density of the 1000-meter diameter sphere just below the ground is 2500 kg / m^3 (which is what it would be if the ball is typical earth-crust material), how much force does it exert on that 1-kg mass in the lab?
I found this force to be 2.25*10^-4N, I found this in my lab notes.
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You need to calculate the force that would be felt at a point near the outer radius of the ball. You should base this is the accurate value of the density of gold.
You will also want to figure out the force that would be felt by the 1 kg mass if the gold sphere was replaced with a rock sphere.
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What’s the difference in these forces?
The differences in these forces is 1.7*10^3N.
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Could we detect the difference in the lab? If so, how?
No I do not think that we could feel this difference in the lab because it is a small increment.
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1.7 * 10^3 N is a very respectable bench-press (over 300 lb). That would be detectable.
What means do we have available to detect forces? What are the smallest forces we could expect to detect using these means?
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