
Helix / Spring Volume
Hello, I need some help learning how to calculate the volume of a Spring. The only resource i can find is on wikipedia, but i am having trouble understanding it.
Please see : Spring (mathematics)  Wikipedia, the free encyclopedia
http://upload.wikimedia.org/math/4/6...e1db052d75.png
This is the forumula they give.
where
R is the distance from the center of the tube to the center of the helix,
r is the radius of the tube,
P is the speed of the movement along the z axis.
Ok, the helix will be 400 wide, so R = 200 units.
The radius of the tube will be 30, so r = 30 units.
Now this is where im stuck, they ask for P for the speed it moves upwards / downwards. How should i get this? For example if i want my spring to have 2 complete revolutions and have a total height of 500 units, how should i know what P is?
I also need to know n, which is not explained very well what n is on the page.
Many thanks if you can help me understand.

Your helix has radius 200 and the tubing as radius 30. Correct?. This conflicts with R which says they're both 200.
In this event R+r=230. That's what I'll use.
Assume you're wrapping a tube of radius 30 around a helix of radius 200,
This forms a helix. A helix can be represented by $\displaystyle x=acos(t), \;\ y=asin(t), \;\ z=ct$
a in this case is R+r=230. The radius of the helix + radius of tubing.
Since you want two revolutions when z=500 units, you have $\displaystyle c=\frac{500}{4\pi}=\frac{125}{\pi}$
You have the helix: $\displaystyle (230cos(t))i+(230sin(t))j+(\frac{125}{\pi}t)k$
It's length in making two revs in a distance of 500 units is given by
$\displaystyle 2\pi\sqrt{230^{2}+(\frac{125}{\pi})^{2}}\approx{14 66.6}$
Now, this is a cylinder of radius 30 with height 1466.6
$\displaystyle {\pi}900(1466.6)=4,146,713.8 \;\ $
Check my calculations out.

Wow thanks for taking the time to explain that to me more clearly.
Hopefully your message will help others aswell if they find this through a search engine.