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Springs in series and parallel - HSN forum

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Springs in series and parallel


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#1 dfx

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Posted 30 October 2005 - 07:39 PM

For two springs in series with the same spring constant, k, the effective total spring constant = k/2, and for parallel = 2k.

Then if F = kx

Then this implies that you need a force F to extend by an extension x.

For series springs:

 F =\displaystyle \frac {kx}{2} \Rightarrow 2F = kx

So this would imply that for an extension x, you need a force 2F.

And for parallel springs:

 F =2kx \Rightarrow \displaystyle \frac{F}{2} = kx

So this would imply that for an extension x you need a force F/2

This is totally contradictory to my experimental results and logic. For a spring in series, you need half the force F to achieve an extension x - logically since the force on the lower spring also pulls down on the upper spring etc. For parallel springs you need twice the force 2F to achieve an extension x - logically since the force is evenly distributed over 2 springs, so twice the force needed.

Why is this contradictory? Is my mathematical reasoning flawed?





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