Ineverted proportionality is when oone varible changes by an increase the other one decreases. We can see it on the graphs how it decrease.

we can see the same with it 

we can see as the thickness increaces the force decreaces 

What is proportionality

1)Proportionality is when you have two results are nearly the same and when one dubles the second dubles also

to fine proporsi you need to look if ot gose throw 0.0 or if you divied X equaly you get the same result