How Do You Calculate the Spring Constant (N/m) from a Given Load?

[jameslat]

Hey all,
I'm working with springs and I curious as to how I find out the N/m of any given spring.
like if the maximum work load of a spring is 20 pounds how could I figure out the N/m of it (or the 'k', the spring constant, or what information about the spring do I all need to determine the constant in N/m if it is not given by the company?

Also can I establish a ratio? (random example) Like if a a 20 pound spring has 2 N/m would a 100 pound spring have 10 N/m ?

Or if I'm completely going in the wrong direction with this, please help direct me in the right one.

Any input would be most excellent!
Thanks!
-James

 

[jameslat]

Also a quick note, would it be easier if I knew that it was 20 lbs/in ?

thanks again!

 

[Naty1]

Knowing the maximum working load of a spring will not in general be helpful in determining the spring constant, k. The maximum working load is likely related to the safe weight that can be utilized without either deforming or damaging the spring in some way...as in breaking it.

http://en.wikipedia.org/wiki/Spring_constant

explains that the spring consant k assumes stress is proportional to strain; that is, the deformation is linear, which is appropximately true when the spring is not permanently deformed...So this means that if a given load extends the spring some distance, twice that load will extend the spring twice that distance...k is a constant

From that description you should be able to figure out the k for any spring:

Hang a weight on a spring and measure the extended (increased) length of the spring...keeping your units consistent, of course...divide the force (weight) by the length difference...that's k...

 

[jameslat]

Isn't the k measured in N/m though?
So if a 20 pound/in spring would have 2.257 N/m.
would this be the same as the k?
k=2.257?