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?

 

[PJC01]

Hello James,

Calculating the N/m of a spring, also known as the spring constant or stiffness constant, can be done by using Hooke's Law, which states that the force exerted by a spring is directly proportional to the displacement of the spring from its equilibrium position. In other words, the stiffer the spring, the more force it takes to stretch or compress it.

To calculate the spring constant, you will need to measure the displacement, or change in length, of the spring when a certain force is applied to it. This can be done using a force gauge or a scale. Once you have this information, you can use the formula k = F/x, where k is the spring constant, F is the force applied, and x is the displacement.

In your example, if the maximum work load of a spring is 20 pounds, and you know the displacement when this force is applied, you can use the formula to calculate the spring constant in N/m.

It's important to note that the units for the spring constant will depend on the units used for force and displacement. If the force is measured in pounds and displacement in inches, the spring constant will be in units of pounds per inch (lb/in). To convert this to N/m, you can use the conversion factor 1 lb = 4.448 N and 1 in = 0.0254 m. So the spring constant in N/m would be 4.448/0.0254 = 174.98 N/m.

To answer your question about establishing a ratio, it's important to understand that the spring constant is unique to each spring and is not directly proportional to the weight or force applied. So a 20 pound spring with a spring constant of 2 N/m does not necessarily mean that a 100 pound spring will have a spring constant of 10 N/m. The spring constant will depend on the specific characteristics of the spring, such as its material, dimensions, and design.

I hope this helps guide you in the right direction. If you have any further questions or need clarification, please don't hesitate to ask. Best of luck with your research!