String Held Up in Tension

Saw this image online today, and was pretty fascinated by it.

I decided to do a quick free body diagram to get a better sense of how exactly tension was distributed across the string.

I color-coded the left-side against the right-side so that you can see the forces balanced by being from the same “spring.” As with any freebody diagram, taking any specific section of the string and summing up the forces coming into it from either direction gives us a sense of the net forces on it.

We see here that sections 1,3,5,7,9 are equivalent and 2,4,6,8 are equivalent.  The odd-numbered sections are in tension with force F, while the shorter even-numbered sections are in tension with force 2F.

This of course is a simplified view of the system because it does not take into account any moments of rotation generated by the masses hanging on the string.