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Post by bodrius on Nov 17, 2009 20:16:02 GMT -4
First of all I want to say that I don't believe the moon landings to be fake, but there is something I can't figure out, surely because of my limited knowledge in physics... I know that because there is vacuum on the moon the flag keeps moving more time than what it would on Earth, because there is no air friction. But if there is no friction what makes it stop then? Gravity?  |
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Post by Jason Thompson on Nov 17, 2009 20:23:06 GMT -4
Essentially, yes. There is a constant force downwards. The flag under gravity ultimately will find the position of least gravitational potential, which is hanging vertically.
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Post by AtomicDog on Nov 17, 2009 20:45:04 GMT -4
Even without air, the flag does have internal friction against the pole.
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vq
Earth
What time is it again?
Posts: 129
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Post by vq on Nov 17, 2009 21:31:51 GMT -4
A "waving" flag is constantly bending the individual nylon fibers in the cloth. Bending something this way converts some of the kinetic energy (motion) into heat, which means the flag starts to move more slowly.
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Post by echnaton on Nov 17, 2009 23:27:04 GMT -4
Some portion of the flags motion will be transferred into the pole then into the ground. There are many ways to dissipate the energy. Internal friction of the cloth is probably the greatest.
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Post by randombloke on Nov 18, 2009 8:17:20 GMT -4
No air is not the same as no friction, it just means no air resistance. Other damping effects on motion include: Internal friction between the nylon fibres; mechanical stresses within individual nylon fibres; friction between the flag and the pole; mechanical damping of vibrations within the pole due to internal stresses; and (completely insignificant relative to the others of course, but still present) loss of fibre elasticity due to radiation damage, mostly UV.
I probably missed a couple too.
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Sabine
Mercury
A closed mouth gathers no foot
Posts: 12
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Post by Sabine on Nov 18, 2009 12:48:25 GMT -4
Wasn't there a wire running along the top edge to hold the fabric out in a nice rectangle? I always assumed that after being bumped, that wire was simply returning to it's previous shape and position. Like branch of a tree when you pull it down and then let it snap back up again.
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Post by laurel on Nov 18, 2009 14:09:08 GMT -4
Wasn't there a wire running along the top edge to hold the fabric out in a nice rectangle? I always assumed that after being bumped, that wire was simply returning to it's previous shape and position. Like branch of a tree when you pull it down and then let it snap back up again. That's right. If you look closely at a photograph like this one from Apollo 17, you can clearly see the thin rod at the top of the flag that is making it stand out horizontally. www.hq.nasa.gov/alsj/a17/AS17-134-20382HR.jpg |
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Post by echnaton on Nov 18, 2009 14:39:12 GMT -4
Wasn't there a wire running along the top edge to hold the fabric out in a nice rectangle? I always assumed that after being bumped, that wire was simply returning to it's previous shape and position. Like branch of a tree when you pull it down and then let it snap back up again. It was an extendable rod. On A-11 the rod would not fully extend, making the flag look more like it was waving. www.nasm.si.edu/imagedetail.cfm?imageID=2192 |
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Post by randombloke on Nov 18, 2009 17:13:49 GMT -4
And on the others, they deliberately didn't extend the rod because they liked the illusion of apparent motion that it produced.
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Post by laurel on Nov 18, 2009 17:30:11 GMT -4
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Post by bodrius on Nov 18, 2009 19:51:12 GMT -4
Thanks everybody for your answers...  |
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