[strav]

Actually, the boy pulls on the rock (centripetal force) and the rock pulls on the boy (centrifugal force). The string is the medium through which these equilibrants do battle.

Thanks for replying yoda.

Ok. There's a hair which may need to be split depending on whether the string's mass can be ignored, but so far so good.

Are we agreed that centrifugal force does affect the boy but in any way affects the rock?

While we are hair splitting - are they both equilbrants or is one a resultant?