Re: Doc: NR 4.1.2: Reorganize vertical dimensions. (issue2316042)

[Trevor Daniels]

markpolesky wrote Saturday, October 02, 2010 5:09 PM

> Okay, here we go...
>
>   Hooke's law:  F=-kx
>
>   "x" is the displacement of the end of the spring
>   from its equilibrium position (in SI units: "m");
>
>   "F" is the restoring force exerted by the material
>   (in SI units: N or kg·m/s^2); and
>
>   "k" is the force constant (or spring constant) (in
>   SI units: N/m or kg/s^2).
>
> So, according to Joe, stretchability is equal to 1/k.  So, if we 
> use "s"
> for stretchability, then
>
>    F=-x/s

That's not really needed.  Here's the point:

For each spring  y = -sF, so dy = -sdF  (1)

When the contents of a page are being stretched the
same force is applied to every spring, so the ratio
of the increase in length of any two springs is equal
to the ratio of their stretchabilities.

So if you need to stretch the contents of a page by
an amount y, y = sum(dy's) = -dF sum(s's)

sum(s's) is known, a constant, so that gives dF, and
then all the separate dy's can be calculated from (1).

Units are irrelevant, as it's only the ratios of the
s's that are important.

Trevor