Springs experiment, with a graph of length against mass

[jack edison]

Homework Statement

Say if I had a system with 3 springs on the left, 1 spring in the middle, and another 3 springs on the right. I add masses to the central spring and calculate the extension. After all my measurements, I plot a graph of spring against mass. If I then repeat the experiment again, but with removing the central spring, how would the graph change?

Homework Equations

The Attempt at a Solution

I think the graph initially is a straight line to begin with, before curving off. Without the central spirng, the graph becomes a straight line

 

[CWatters]

I think the graph initially is a straight line to begin with, before curving off. Without the central spirng, the graph becomes a straight line

So initially 7 springs then 6 springs.

Why would one be "curving off" and the other straight? Why a difference between 6 and 7 and not between say 8 and 9 or 3 and 4?

Got a drawing?

 

[jack edison]

the springs are attached to a ruler, with another ruler directly beneath it. The 'extension' is the distance between the top of the 2 rulers.

 

[CWatters]

Are the rulers rigid?

If they are then the load on the bottom one should be transmitted uniformly to all the springs. So I'd expect a straight line for both provided the springs aren't overloaded (eg they stay within their linear range).

If the rulers bend then the middle spring will be stretched more than the outer springs.