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[Phys-L] hands-on activity: Dirac String Trick

Here is something students can do at home. It takes only
a few minutes, but changes how you think about the universe.

Consider a situation where rotating something by 720° is
in some sense the same as no rotation at all. You might
think that a 360° rotation would work just as well – but
this is not true!

The experiment can be done using cardboard, string, and
a little bit of tape. A discussion, with a diagram and
some references, can be found here: