SPRING CONSTANT- simple harmonic motion

[linyen416]

I'm investigating damped oscillations using a mass held between two springs.
In the experiment, I measured the spring constant using a method which now doesn't make sense.

I measured it by hanging masses from ONE vertical spring and graphing the force exerted by spring (mass times 9.8) against the elongation of spring

I think that's wrong. I think I should have used a pulley or something like this:
the glider is held between two springs. Record its equilibrium
position.
2. Attach a piece of audio tape to the glider and lay it across the “air
pulley” with a small mass suspended on the end of the tape.
3. Measure the displacement of the glider from equilibrium for 4
different hanging masses.
4. Graph the weight of the hanging mass (y axis) vs. the measured
displacement.

But I don't even understand how this method works. What does it mean by attaching a piece of tape to the glider and laying it across the 'air pulley'?

My second and main concern is that because I cannot redo the experiment, I have to somehow use the k values that I've measured using the masses hanging on the single spring. How can I fix the k values to get one that will equal the k value resulting from two springs, one on each side of the mass?

URGENT!
any input appreciated!

 

[Doc Al]

I measured it by hanging masses from ONE vertical spring and graphing the force exerted by spring (mass times 9.8) against the elongation of spring

That's a perfectly fine way to measure the spring constant. I assume you measured the spring constant of each spring?

My second and main concern is that because I cannot redo the experiment, I have to somehow use the k values that I've measured using the masses hanging on the single spring. How can I fix the k values to get one that will equal the k value resulting from two springs, one on each side of the mass?

How do you find the effective spring constant of the two springs together? Hint: With a spring attached to each end, is the effective spring constant greater or less than each individual spring constant?

To figure that out, imagine the mass between both springs in equilibrium. Pull it a distance X to one side. What net force (due to both springs) acts on the mass? Set that net force equal to KX, where K is the effective spring constant.

 

[linyen416]

I think I know what you're saying Doc. If you put two springs in seires then the effective spring constant is k times two

But my situation is where the mass is held BETWEEN the two springs.

 

[linyen416]

So I think one way to get the effective spring constant is to use a pulley somehow.

 

[linyen416]

unless there's an equation that relates the individual spring constants to the effective spring constant when the mass is held between two identical springs

 

[Doc Al]

I think I know what you're saying Doc. If you put two springs in seires then the effective spring constant is k times two

You have it backwards.

But my situation is where the mass is held BETWEEN the two springs.

I know.

So I think one way to get the effective spring constant is to use a pulley somehow.

Huh? No need to complicate things by adding a pulley to the mix.

The way to get the effective spring constant is to do what I said in my last post. (You'll have to apply Hooke's law.)

unless there's an equation that relates the individual spring constants to the effective spring constant when the mass is held between two identical springs

Of course there is. But rather than look for such an equation in a book (you might get lucky!), just figure it out for yourself by doing what I suggested.