> My question: is the force excerted by the elastic linearly or
quadratically
> proportional to the amount you stretch it?


I believe the force is described by F = -kd, where k is some constant
describing how springy it is (higher k = greater force = stronger
springiness) and d is how far it's being stretched. So, yes, it's linear,
and the difference between a stretchy or rigid bit of elastic is the
constant k.

I forget what law this is... it's someone's "spring law" or something like
that. Learned it in high school Physics but I forget the guy's name...

 - Slime
 [ http://www.slimeland.com/ ]

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On Mon, 20 Oct 2003 01:56:56 -0400, "Slime" <fak### [at] emailaddress> wrote:

>
>I forget what law this is... it's someone's "spring law" or something like
>that. Learned it in high school Physics but I forget the guy's name...

Hook's law I & II

Regards
        Stephen

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> >I forget what law this is... it's someone's "spring law" or something
like
> >that. Learned it in high school Physics but I forget the guy's name...
>
> Hook's law I & II

Yeah... that sounds familiar now you mention it...

OK, so the force exterted by the spring/elastic/whatever is simply some
multiple of the amount of distortion the thing undergoes? Cool - that's the
way I coded it! (Was initially inverse-square, like gravity... but I wasn't
sure that was physically correct...)

Thanks.
Andrew.

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On Sat, 25 Oct 2003 17:07:50 +0100, "Andrew Coppin" <orp### [at] btinternetcom>
wrote:

>Cool - that's the way I coded it!
Yes, it is linear up to the limit of elasticity IIRC


Regards
        Stephen

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> >Cool - that's the way I coded it!
> Yes, it is linear up to the limit of elasticity IIRC

...that being the point at which is snaps, yes? ;-)

Thanks.
Andrew.

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On Sat, 25 Oct 2003 22:37:25 +0100, "Andrew Coppin" <orp### [at] btinternetcom>
wrote:

>...that being the point at which is snaps, yes? ;-)

No, IIRC It is the point where the material either stops being elastic or stops
having a linear deformation. 
A picture(graph) is worth a thousand words.
http://has.ied.edu.hk/has/forum/phy/messages/23.htm

Regards
        Stephen

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> >...that being the point at which is snaps, yes? ;-)
>
> No, IIRC It is the point where the material either stops being elastic or
stops
> having a linear deformation.
> A picture(graph) is worth a thousand words.
> http://has.ied.edu.hk/has/forum/phy/messages/23.htm

Mmm... if only certain lecturers I met has such good handwriting ;-)

But seriously... that's more detail than I need for my simulation.
Interesting to know though. (I'm ever curiouse...)

Thanks.
Andrew.

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On Sun, 19 Oct 2003 21:55:45 +0100, "Andrew Coppin"
<orp### [at] btinternetcom> wrote:

>Any hints on how the real physics works would be appreciated.

Others already mentioned Hooke's Law, I will just add minor but
important details.

Hooke's Law relates stress, strain and Young's modulus of elasticity. 

Stress is absolute (not mathematically speaking, but physically
speaking). It is measured in N/m^2 can be basically considered to be
equivalent to pressure. Note that the denominator represents area,
i.e. a cross-section, so for uniform cross-sections (like a bar) it
can directly represent force. Stress is a tensor but for simple 1-D
problems can be treated as a numeric value.

Strain is a relative quantity (this is important) and shows how much
the object has "stretched". Technically, it is a tensor, like stress,
but the case of long, thin objects can be treated as one-dimensional
and thus purely algebraic. Strain is defined as (L - L_0)/L_0 or in
words, the change in length (positive if stretching, negative if
compressing) divided by the original length.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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