Let's say I have a spring with length of $80$m.
The spring is connected horizontally between two masses (on a table, without friction).
Lets say the string got narrower to $76$m.
Does it mean that $\Delta X$ of the two bodys is $2$m? or each one of the masses has $\Delta X=4$m?
It is a debate between a friend and me, he says its $4$m, I say its $2$m ( Think of an accordion, move it symmetrically to the inside, each one of the two sides moves equally half the $\Delta X$ ).
Any answers to our debate will be welcomed.