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  1. Why can't we fly?

  2. It contradicts with our known laws of physics, but which one?

  3. Is it possible that once we know gravity better we would be able to fly using some sort of anti-gravity machines like in movies?

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closed as off-topic by John Rennie, Qmechanic Nov 28 '14 at 10:45

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    $\begingroup$ How do you define an anti-gravity machine? $\endgroup$ – Berrick Caleb Fillmore Nov 28 '14 at 1:53
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    $\begingroup$ do air planes count...? $\endgroup$ – Carlos - the Mongoose - Danger Nov 28 '14 at 1:56
  • $\begingroup$ Did you hear about anti-gravitons? $\endgroup$ – Sofia Nov 28 '14 at 2:10
  • $\begingroup$ I mean flying without our present technology but make use of hypothetical anti-graviton. you see UFOs do that? $\endgroup$ – user17755 Nov 28 '14 at 2:13
  • $\begingroup$ How do you know UFO's don't use conventional propulsion technology to fly? $\endgroup$ – Kyle Kanos Nov 28 '14 at 3:01
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There's a lot of reasons why we can't fly like superman/Rocky the Squirrel/birds. We should note the flying involves movement through the air controlled by the flyer which can carry on indefinitely. If you're looking for something else, you should know about squirrel suits and jet-packs.

Lift

is the number one reason why we can't use our arms to fly. The air is too thin, our arms are too small (in surface area to mass ratio), those arms are shaped wrong, and gravity is too strong.

There are a lot of factors which go into making things fly. Wikipedia has a good summary of what goes into in their article on lift. Determining if something will fly can be very difficult, so expect advanced math.

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The real problem with a workable anti-gravity device (assuming it could be made) is how to power it. It will most likely need an electrical power supply. For example, a Boeing 747 needs about 100MW of power to get into the air, and it's thrust to weight ratio is about 1:6 which means that your anti-grav installed on a 747 would need a half gigawatt power supply to just lift off the ground. That would probably weight more than the entire aircraft. Going nuclear, with all the shielding, would be even worse. This is even before we think about accelerating beyond 1G

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