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I'm trying to determine the viscous dampening coefficient of a spring $c$. Read about it on Wikipedia here.

The two equations which I have are: $f=-cv$ and $ma+cv = -kx$

I know the spring constant $k=5$, the mass is $50\text{ }\mathrm{g}$ and the initial amplitude of the spring is $10\text{ }\mathrm{cm}$.

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Dear @MathsStudent: Fortunately, I answered your question already: physics.stackexchange.com/questions/8495/… Greets –  Robert Filter Apr 17 '11 at 10:14
    
Thanks Robert, but you didn't really. I can't use your equation (angular frequency = etc) as I don't know the angular frequency. It seems that the dampening coefficient is impossible to figure out, as not enough variables are ever known! –  MathsStudent Apr 17 '11 at 10:23
    
This is the third nearly identical questiion from You on "springs"!The problem is that You did not understand the answers to both of Your earlier questions. One thing I'd recommend, is: change Your "nome de guerre". Vote to close –  Georg Apr 17 '11 at 10:36
    
@MathsStudent: I think we have a problem of misunderstanding here. I think I pretty much answered your question. Please be specific in what you don't understand and what you mean by determining (measuring, calculating). In addition it might be useful to know at which point of your study you are and what intention you have with these spring questions. Greets –  Robert Filter Apr 17 '11 at 10:40
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@MathsStudent: Ok, you really mean calculation not measurement. Given $m$ and $k$ and the initial amplitude, your question cannot be answered. Remember, this is a constant you put in your model, you cannot derive it from it. Greets –  Robert Filter Apr 17 '11 at 11:31

2 Answers 2

up vote 3 down vote accepted

with the given $m$ and $k$ you indeed cannot calculate the damping coefficient $c$.

Remember that you just have a model where you put some constants in and you can only derive other constants which somehow depend on them.

The question concerning an actual measurement was answered in Investigating the dampening of a spring.

Greets

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Okay, so what do I need to calculate c? As is obvious, I don't understand the maths behind the problem. If possible, can you just make up the data required and do an example calculation to find 'c' for me? –  MathsStudent Apr 18 '11 at 11:04
    
@MathsStudent: As I said, in a mathematical model you just define $c$. Calculation is only possible if you have a relation between different variables of a model such that the one you are looking for is already determined by the others. Greets –  Robert Filter Apr 18 '11 at 17:33

fs=-kx this is Hooke's law if you look up Hooke's law you should find what the spring coefficient is as it is part of the Hooke theory

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