Increase in length directly proportional to the origin length

[Check_1831]

Hi all,

When an object is heated , why is the amount of change in its length directly proportional to the original length ? I have read that the increase in length it is directly proportional to the initial length in most of the articles. But I wanted to know how this proportionality arrived at ??

 

[jbriggs444]

If one meter stick expands by 1 mm when heated by some amount then two hot meter sticks laid end to end will longer by a total of 2 mm.

And each half of a hot meter stick will have expanded by 1/2 mm.