basic opposing springs question

[JonnyRotten]

Hi folks,

I'm sure this is a simple question but here goes. I have a plate with 2 coil springs, 1 pushing from each side of the plate. Each with a force of 5Lbs. So the plate is at equilibrium. For argumments sake, lets say each spring is identical with a spring rate of 1Lb/in. If i then add an external force of 1Lb to the plate then what happens to the force and displacement? Would it move 0.5" in the direction of the external load? Which means it decreases the load from 1 spring to 4.5Lbs and increases the load in the other spring to 5.5Lbs? So have I effectively doubled the spring rate?

Thanks

Jonny

 

[dgallup]

Looks right to me.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[israelkk]

The double rate is trivial because you use two springs in parallel. The nice idea here is that the two parallel springs don't start from zero load but from the 5 lb preload. However, the springs are always preloaded and relaxtion and creep should be considered

 

[JonnyRotten]

israelkk, can you explain why the double rate is trivial please?

Thanks

 

[israelkk]

Because they do not see the same force. When one is pressed the other is released. When they are working in series they see the same force. The only change here from classic parallel spring arrangement is that one spring has a "negative rate" and the other "positive rate".

 

[JonnyRotten]

Yeah I understand that - but ultimately I have doubled the spring rate. If i had a single spring with a rate of 1Lb/in, for every extra 1Lb added then it would compress 1". But with the 2 spring arrangement that I have described above then it only compresses 1/2" for every extra 1Lb added.

 

[israelkk]

That's what I said, you have two springs in parallel therefore, the rate is doubled. This is why I said it is trivial.