One of the guys is one guy among a group of the guys. Adding an apostrophe forms the possessive plural guys':


  One of the guys' swords


The word guys' is possessive plural, and the meaning of the sentence is ambiguous, depending on whether one modifies swords or guys:


  One sword from a group of swords belonging to the guys.
  
  Or
  
  The swords belonging to one of the guys.


In one of the guy's swords, the word guy's is possessive singular, and the meaning is straightforward: One sword belonging to the guy.

What is the correct possessive form of "One of the guys"?
One topic which was covered in university, but which I never understood, is how a spinning top "magically" resists the force of gravity. The conservation of energy explanations make sense, but I don't believe that they provide as much insight as a mechanical explanation would.

The hyperphysics link Cedric provided looks similar to a diagram that I saw in my physics textbook. This diagram illustrates precession nicely, but doesn't explain why the top doesn't fall. Since the angular acceleration is always tangential, I would expect that the top should spiral outwards until it falls to the ground. However, the diagram seems to indicate that the top should be precessing in a circle, not a spiral. Another reason I am not satisfied with this explanation is that the calculation is apparently limited to situations where: "the spin angular velocity $\omega$ is much greater than the precession angular velocity $\omega_P$". The calculation gives no explanation of why this is not the case.
