What does it mean when we say a variable changes linearly?

linear-algebra algebra-precalculus simulation

I know that probably my question is a bit silly/simple but I will be thankful if anyone could help me. I have attached a screenshot in which a variable is defined for an object somehow that it linearly decreases from 500 micrometers at the top of the object to 50 micrometers at the bottom of the object. I was wondering what does it mean by linearly decreases? I know that it means that the variable decreases slowly from top to bottom of the object but can anyone explain the linear decrease in more detail?

Any response or feedback would be highly appreciated.


Two variables $v_1$ and $v_2$ having a 'linear' relationship in this context probably means that the function relating them is affine (has a straight-line graph $v_2=m\,v_1+c$ for some nonzero $m$); in other words, there is some constant $c$ such that $v_2-c$ is directly proportional to $v_1.$

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