Finding the force on a spring (Fs)?

[MuffinMerc]

Homework Statement

I'm trying to find the force of a spring (Fs) from the mass of the weights, and the extension of the spring. The springs length without a weight attached was 5 cm. The lab we did had us put 5 different weights on the same spring, and graph the results.

My results from the lab:
0.05 kg, spring stretched 0.021 meters.
0.1 kg, spring stretched 0.055 meters.
0.2 kg, spring stretched 0.115 meters.
0.3 kg, spring stretched 0.18 meters.
0.4 kg, spring stretched 0.25 meters.

Now, I don't know how to figure out the Fs (force on the spring) on each of these 5 results.

Homework Equations

I'm asking for an equation that can help me. So far, Fs=-kx has proven useless at the moment.

The Attempt at a Solution

My lab partner used Fs=mass X gravity to find force spring. I'm not sure if this is correct, because on the graph (Fs vs extension (x) graph) the line is supposed to be linear and straight, but my graph with the plotted points looks nothing like that when the dots are connected.

Any help would be appreciated.

 

[PhanthomJay]

Looks like you have some measurement errors. If it stretched 0.115 m with .2 kg, then with .1 kg, it ought to stretch half as much, or about 0.055 m or so. Did you miss a decimal point?

 

[MuffinMerc]

Looks like you have some measurement errors. If it stretched 0.115 m with .2 kg, then with .1 kg, it ought to stretch half as much, or about 0.055 m or so. Did you miss a decimal point?

Oh yes, you're right! Typing error, I fixed that now.

Should make a little bit more sense now.