Ask questions, find resources, browse the virtual shelves.

## Will the free end of the pole exceed the speed of light?

Yes, the math shows it does, and this does not violate any physical laws.
116
14%
No, the pole end cannot exceed the speed of light.
666
79%
Where's the barn? I heard this paradox involves a barn.
59
7%

RJN
Baffled Boffin
Posts: 1670
Joined: Sat Jul 24, 2004 1:58 pm
Location: Michigan Tech

Guess the Result of the Experiment of the Day (GRED): The Twirling Pole Paradox

You hold a really long pole -- for example one light year long. You are out in space. You hold one end of this pole firmly to your stomach with the pole pointing out, and then you spin around in a circle. Therefore the free end of the pole makes a complete circle, with you at the center of the circle. Say it takes you 10 seconds to do this. Does the speed of the free end go faster than the speed of light?

Please do NOT post any answers or comments with spoilers here. Answers and comments with spoilers are encouraged in GRED Answer post here: http://asterisk.apod.com/vie ... 30&t=19643 . Please check back there later -- what I believe to be the correct answer will be posted there a few days after this initial post.

Comments or questions here -- without spoilers -- are OK. In particular, questions about the experimental setup are OK.

Nancy Lou
Asternaut
Posts: 1
Joined: Thu Jun 03, 2010 7:54 pm

### Re: GRED: Twirling pole paradox

I'm a professional musician and educator. I LOVE these questions that I find on APOD. Sometimes, I even may have the answer correct!
Thank you for helping to keep my old brain sharp!

Jay Mack

### Re: GRED: Twirling pole paradox

The poser does not specify the speed of light in relation to what. Speed is relative.

Beta
Ensign
Posts: 35
Joined: Thu May 27, 2010 3:39 pm

### Re: GRED: Twirling pole paradox

Jay Mack wrote:The poser does not specify the speed of light in relation to what. Speed is relative.
Actually, the speed of light is the one speed that isn't relative.

Nurse Mike

### Re: GRED: Twirling pole paradox

Can we assume the pole is a "standard" pole, or does it have infinite rigidity?

Einstien

### Re: GRED: Twirling pole paradox

The question doesn't seem to make sense.
If it is given that it took 10 seconds to spin around, the pole must have moved in a 1-lt-yr arc. (That's C = pi*D = pi*2-lt-yr) That's pretty fast!
If this is given, then the pole spun around and did not break and made the arc. Given.

Answer a) asks if it doesn't violate any laws....wha?! Of course it does, so this must be wrong.
Answer b) states that the pole can't go faster than the speed of light...which it can't...but, IT JUST DID in the given part of the problem!..so this must be wrong.
Answer c) is correct by the process of elimination.

RJN
Baffled Boffin
Posts: 1670
Joined: Sat Jul 24, 2004 1:58 pm
Location: Michigan Tech

### Re: GRED: Twirling pole paradox

Nurse Mike wrote:Can we assume the pole is a "standard" pole, or does it have infinite rigidity?
Assume the pole is made of a very sturdy solid material.

jman
Ensign
Posts: 73
Joined: Thu Apr 08, 2010 2:31 pm
Location: Calgary, Alberta

### Re: GRED: Twirling pole paradox

It's a Festivus Pole. Very high strength-to-weight ratio