Hooke's Law

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Hooke's Law

I have designed the experiment to measure spring constants when the

springs are in series and in parallel. The theory is based on Hooke's

law which is:

F = kx

where F = Force, k = Constant and x = Extension [Ref. 1].

Unfortunately with the springs I have, I can only measure extension,

not compression for which Hooke's is also valid.

Prediction

Single Spring:

Hooke's law, where F = kx. I predict that I if I plot Force on the Y

axis and extension, x, on the X axis, it will be a straight line and

the gradient will be the spring constant.

Parallel Springs:

In the diagram above, T1 is the tension in spring 1, and T2 is the

tension is spring 2. So T1 + T2 has to equal the Force, F. I assume

the two springs are originally the same length and the extensions are

the same in both springs. So this means that T1 = k1x and T2 = k2x. So

by knowing this, you get the formula:

F = k1x + k2x = x (k1 +k2).

So overall, the spring constant for the two springs is k1 + k2. For

the graph, my prediction is the same as for a single spring as

mentioned earlier but with a different constant.

Springs In Series:

In this diagram, T1 is the tension in spring 1, and T2 is the tension

is spring 2. If I ignore the mass of the 2nd spring, the two tensions

have to be equal and both equal to the force. I have to find a final

expression in the form F = k (x1 + x2) because x1 + x2 is the total

extension. So from Hooke's law you can get x1 = F / k1 and x2 = F / k2.

Knowing this, gives me a new formula: F = k (F / k1 + F / k2). Here,

you can then take out the common factor, F and divide both sides by kF

which gives you a final formula: 1 / k = 1 / k1 + 1 / k2 .

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