# Is There a Formula for Cross Sectional Area? ?



## wll (Oct 4, 2014)

Is there a formula for a cross section of rubber tubing ?

wll


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## Emitto (Sep 11, 2013)

You can do it this way

A=π(R2﹣r2)

R: outer radius and r:inner radius


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## Chuck Daehler (Mar 17, 2015)

The greek/math symbol pi in the formula is a number, sufficed to be for this purpose, 3.1416. And r means "radius". There are two radii, one for the inner circle and for the outer one. You would need a magnifier for slingshot elastic, of say 5x or more, and preferably a mounted one to free both hands, and a very good caliper mic, preferably a digital one or one with an exceedingly good vernier to ascertain the correct measurements. Many times these measurements are given by the seller of the tubing...or a wall thickness number that you can use with arithmetic to figure the numbers.

As any tubing stretches, the measurements change infinitely...the thinner it gets with stretch and thicker it gets with retraction...just thought I'd add this obvious point.


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## wll (Oct 4, 2014)

This is way past my math skills !

wll


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## Viper010 (Apr 21, 2012)

Let me make a little effort to try and simplify...

3.1416*outer diameter - 3.1416*inner diameter = wall cross section surface

That can't really be beyond your math skills can it?

If you still don't get it, please post inner and outer tube measurements and I will do the equation for you right here.


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## Imperial (Feb 9, 2011)

Viper010 said:


> Let me make a little effort to try and simplify...
> 
> 3.1416*outer diameter - 3.1416*inner diameter = wall cross section surface
> 
> ...


we americans dont do math


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## wll (Oct 4, 2014)

Viper010 said:


> Let me make a little effort to try and simplify...
> 
> 3.1416*outer diameter - 3.1416*inner diameter = wall cross section surface
> 
> ...


I got that of course but lets say you want to compare 1842 to 1745. I know I will need to turn metric into inch ...no big deal. but I don't think my end #'s are correct.

If you could just do 1842 and from there I'm sure I will get it.

Thank you very much

wll


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## Toolshed (Aug 4, 2015)

Learning about this stuff now. say 1842, does that mean the r1 = .18mm and r2 = .42mm ?? I haven't learned the nomenclature for tubing yet.


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## Toolshed (Aug 4, 2015)

NM....Just one decimal place. Got it


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