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        riddles >> easy >> Revolving Coin
        
(Message started by: THUDandBLUNDER on Sep 13^th, 2003, 2:24am)

Title: Revolving Coin
Post by THUDandBLUNDER on Sep 13^th, 2003, 2:24am

Two touching identical coins lie on a flat table. Coin A is rolled completely around Coin B (without slipping)
and comes to rest in its original position.

Relative to the table, how many revolutions has Coin A made?

Title: Re: Revolving Coin
Post by TenaliRaman on Sep 13^th, 2003, 9:48pm

::[hide] wouldn't the answer be 1 or did i miss something?[/hide]::

Title: Re: Revolving Coin
Post by harpanet on Sep 14^th, 2003, 6:11am

::[hide]If coin B's edge was uncurled and laid out in a straight line then the answer would indeed be 1, but the edge performs its own 360^o revolution, thus adding another revolution to coin A.[/hide]::

Title: Re: Revolving Coin
Post by TenaliRaman on Sep 14^th, 2003, 11:46pm

umm wouldn't that be counted as rotations??

Title: Re: Revolving Coin
Post by THUDandBLUNDER on Sep 15^th, 2003, 2:32am

Quote:

umm wouldn't that be counted as rotations??

REVOLUTION (rµv”…-l›“sh…n) n.
1.a. Orbital motion about a point, especially as distinguished from axial rotation.
b. A turning or rotational motion about an axis.
c. A single complete cycle of such orbital or axial motion.

ROTATION (r½-t³“sh…n) n.
1.a. The act or process of turning around a center or an axis.
b. A single complete cycle of such motion.

[American Heritage Dictionary]

Title: Re: Revolving Coin
Post by TenaliRaman on Sep 15^th, 2003, 8:15am

ok my mistake!!

i misunderstood harpanet's statement totally especially this part ::[hide]but the edge performs its own 360^o revolution, thus adding another revolution to coin A[/hide]::

Anyways i am clear about it now.

[edit]Thanks T&B for the dictionary quotes!![/edit]

Title: Re: Revolving Coin
Post by THUDandBLUNDER on Sep 15^th, 2003, 8:41am

You are welcome, TenaliRaman.

Check out http://mathworld.wolfram.com/CoinParadox.html

Title: Re: Revolving Coin
Post by harpanet on Sep 15^th, 2003, 1:33pm

on 09/15/03 at 08:15:23, TenaliRaman wrote:

...i misunderstood harpanet's statement totally...

It's not the first time that my descriptions have left something to be desired :'( . Fortunately my coding is much more precise 8)

Title: Re: Revolving Coin
Post by TenaliRaman on Sep 15^th, 2003, 10:59pm

Thanks for the link T&B.

@harpanet -- i am sure abt your precise coding :)

Title: Re: Revolving Coin
Post by Sir Col on Sep 16^th, 2003, 8:37am

on 09/15/03 at 13:33:04, harpanet wrote:

Fortunately my coding is much more precise 8)

About that there is little doubt – Euler sends his regards! ;)