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# Wired Equator

67 replies to this topic

### #1 rookie1ja

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Posted 30 March 2007 - 03:56 PM

Wired Equator - Back to the Cool Math Games
The circumference of the Earth is approximately 40,000 km. If we made a circle of wire around the globe, that is only 10 meters (0.01 km) longer than the circumference of the globe, could a flea, a mouse, or even a man creep under it?

This old topic is locked since it was answered many times. You can check solution in the Spoiler below.
Pls visit New Puzzles section to see always fresh brain teasers.

Spoiler for Solution

Spoiler for old wording

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### #2 natterbox

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Posted 28 April 2007 - 06:08 PM

it sounds like you are saying that the wire is oly 10 meters long
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### #3 Veracity

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Posted 18 May 2007 - 07:10 PM

Wired Equator - Back to the Logic Puzzles
The circumference of the globe is approximately 40 000 km. If we made a circle of wire around the globe, that is only 10 metres longer than the circumference of earth, could a flea, a rabbit or even a man creep under it?

Wired Equator - solution
It is easy to subtract 2 equations (original perimeter = 2xPIxR, length of wire = 2xPIxR + 2xPIx(new R)) and find out that the result is 10m/(2xPI), which is about 1.6 m. So a smaller man can go under it and a bigger man ducks.

I’m confused. Are you saying that adding 10 Meters of wire to a perfectly measured 40,000 km of wire that fit snuggly around the planet would give you enough freed up space to elevate the wire 1.6 meters off the ground?? The way the question is worded is " If we made a circle of wire around the globe, that is only 10 meters longer than the circumference of earth" Does that mean you are then using 40,010 meters of wire??? I would think that 10 meters of wire compared to 40,000 would gain you such a microscopic amount it would be almost impossible to measure..

Sorry for the ignorance..
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### #4 rookie1ja

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Posted 18 May 2007 - 09:43 PM

Unbelievable as it may seem, but it is so. Radius of circle made of 40,000 km and 10 meters long wire is just about 1.6 meters longer than the radius of circle made of 40,000 km long wire.

But feel free to prove the opposite.
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### #5 Garrek99

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Posted 19 May 2007 - 02:03 AM

Yeah, this is because the ratio of the input to the output in terms of circumference and radius is 2Pi.
So if you feed it (change in distance) 10m of circumference you will get (change in distance) 1.6m radius. The rest of the puzzle is just there to confuse peops.
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### #6 Veracity

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Posted 19 May 2007 - 02:18 PM

Yeah, this is because the ratio of the input to the output in terms of circumference and radius is 2Pi.
So if you feed it (change in distance) 10m of circumference you will get (change in distance) 1.6m radius. The rest of the puzzle is just there to confuse peops.

Yeah! What HE said!...lol
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### #7 napolinario

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Posted 21 May 2007 - 07:41 PM

No it does not mean having a wire of 40,010 meters but 40,000.01 km. But still, the 0.01km change leaves room for children to walk around.
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### #8 Veracity

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Posted 22 May 2007 - 01:31 PM

No it does not mean having a wire of 40,010 meters but 40,000.01 km. But still, the 0.01km change leaves room for children to walk around.

Well, I suppose the only way I am going to understand how that is possible is to learn Algebra this afternoon, and well, Needless to say, that’s not going to happen.. I am just trying to picture it on perhaps a smaller scale. If you have a basketball, and it is exactly 25 inches in diameter, and you have a piece of string 25.1 inches long.... AHHHH WAIT...lol I DO THIS EVERYTIME. I figure it out when talking about how I can't figure it out. lol

It's the shear scale of the planet that makes such a small amount NOT SO SMALL <--- Moron Math

I would think that placing the string around the basketball would free it up a small amount, but a few feet off the ground IS a small amount with the size of this planet. I SEE,,,, Thanks!
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### #9 schmiggen

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Posted 08 June 2007 - 05:08 PM

There are actually a few other solutions that should be irrefutable based on the wording of the question (although they still feel like cheating). None of them even require the wire to be longer than the circumference.

First, the problem assumes, though it doesn't say so explicitly, that the earth is spherical. Earth is more like a sphere that has been squished in several ways -- I'm not an expert on this, but it may not even be a perfect or near-perfect ellipsoid. So it has several varying circumferences, depending on where you measure it, and I'm not sure the term circumference even actually applies. But assuming you measured the distance around the earth where it was largest, you could easily wrap the wire around at some other circumference-like spot even without making it 10 meters longer and have lots of extra creeping-under room.

But, assuming a different earth that is actually spherical, there is nothing that says your wire has to go around the globe _at_its_great_circle_, or above its circumference. In fact, you could use a wire shorter than the circumference of the earth, and have plenty of room to travel under it, if it were only wrapped around the earth at some other circle than the earth's great circle.

Finally, assuming that the earth is essentially spherical and that the wire does in fact go around over its circumference, the wire can be pulled as tight as one can imagine pulling it (without breaking the wire or slicing into the earth, of course) and there will be SOME point at which any living thing should be easily able to creep under it. Examples are mountain valleys and bodies of water. If you bend the wire so that it follows the ground along these places, then it would have to be much longer than otherwise, so there is some ambiguity about what the circumference of the earth actually means. Earth is not a smooth surface by any standards.

But still, those feel like cheating answers somehow.
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### #10 sphinxteroonicat

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Posted 13 June 2007 - 01:39 PM

Well, the way I make it is
C= 40000000M therefore (Cx3.142857143/2=r) the Radius is 62857142.86 M
C= 40000000 + 10 is C = 40000010M therefore the radius is 62857158.57 M
62857142.86 - 62857158.57 is 15.71428571M.

Your answer of 1.6 M would be correct if the wire were only 1 M longer.

Or have I missed it completely?
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