I have to write a lab report on coil springs and what characterizes them. So, I decided to use several different coil springs. I hanged different weights on them. I proved Hooke's law. But, I think there is something missing. The teacher asked me to say what characterizes springs. I don't understand what has an influence on the ''k'' constant. I know it is related to the stiffness of the spring, but what in the spring makes it stiffer and less likely to stretch? I tried looking up on Google, no result. All I could find was Young's modulus, but it seems too complicated for someone in grade 11.