Why does the spring constant go down after a specific mass?

[boii]

I have been conducting a lab to find the force of a spring by calculating the oscillatory motion of the period. Each time i added a mass, i gained a higher spring constant, but on the 250g i ended up losing spring constant. I was wondering if anyone know why, or if i have done something wrong? The thumbnail i posted will have a better description of what i am trying to say.

 

[hilbert2]

That's just because in practice, real-life springs behave nonlinearly (don't perfectly obey Hooke's law). In other words, the spring potential energy is not just $V=\frac{1}{2}k(x-x_0)^2$ but also contains higher order terms in $(x-x_0)$. Hooke's law works well only for small displacements.

 

[boii]

That's just because in practice, real-life springs behave nonlinearly (don't perfectly obey Hooke's law). In other words, the spring potential energy is not just $V=\frac{1}{2}k(x-x_0)^2$ but also contains higher order terms in $(x-x_0)$. Hooke's law works well only for small displacements.

So for this instance on my lab report, should i record down because it doesn't perfectly obey hooke's law?

 

[hilbert2]

Yes, that's what I would write in the report if I were you.