16-03-2010, 17:25
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#1
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User
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Help with a question
I don't understand this question, can anyone help?
the picture is below
A word of warning, the philosopher, Ludwig Wittgenstein urged us never to believe a picture.
Activity 2
Consider the following situation.
An elastic band is wrapped around the world (around the equator say) so that it lies quite taut on the ground.
It is then somehow lifted everywhere above the ground to a height of 1 metre.
A: The question is: by how much has the elastic stretched?
B: The question is: did the colour add anything; did showing a picture of part of the whole earth have an effect?
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16-03-2010, 17:34
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#2
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cf.mega poster
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Re: Help with a question
A. What's the difference in circumference between that of the Earth, and that of the Earth if it's diameter was 2m wider.
B. No. Obviously not as you didn't understand the question.
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16-03-2010, 17:55
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#4
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BOFH :D
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Re: Help with a question
But what was asked was not wittgenstein's puzzle. the string in the OP's question was raised uniformly by 1m, not lengthened by 1m
therefore..
Where r is the radius of the earth the circumference becomes 2*pi*r (we shall call this a)
In the question, b becomes 2*pi*(r+1m) therefore the amount the string has stretched becomes b-a or (2*pi*(r+1))-(2*pi*r)
Just a small point but a pertinent one, the problem is with the wording of the initial question.
Of course, the validity of the results is dependent on the earth being a uniform spheroid, which it is not.
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16-03-2010, 17:59
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#5
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Re: Help with a question
@ Damien. Wouldn't the diameter be increased by 2 meters making the difference 6.28 meters?
As this could only be a hypothetical problem I assume that we are to treat the earth as a perfect sphere.
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Last edited by joglynne; 16-03-2010 at 18:03.
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16-03-2010, 18:00
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#6
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cf.geek
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Re: Help with a question
but the diameter is from 1 side to the other, it is the circumference that has increased
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SimianCage
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16-03-2010, 18:06
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#7
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BOFH :D
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Re: Help with a question
The radius, and with it the diameter is increased by the first question in post 1, 'the string is raised by 1m' therefore radius increases by 1, diameter increases by 2. The circumference is therefore increased as a matter of course.
let us for a moment assume a radius of 10m, the circumference is 2*pi*10 which, assuming pi to have the value 3.1415 becomes 62.830m circumference
add 1m to the radius and it becomes 2*pi*11 which is 69.113m a difference of 6.283m
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16-03-2010, 18:22
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#8
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Re: Help with a question
What I find mind boggling is that taking pi to the same decimal point of 3.14 I get the same difference in circumference (6.28 meters) whether the diameter of the sphere is Lord Nikon's 20 meters (+ 2) or my earth diameter of 12756200 meters (+ 2).
My brain hurts and I shall retreat to a darkened room. 
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16-03-2010, 20:33
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#9
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Re: Help with a question
What if they elastic twanged back all at the same time? 
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16-03-2010, 20:41
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#10
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Re: Help with a question
The earth would emit a loud Owie!! 
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