brews the rotating identical spheres makes a good action reaction pair example we'll begin with the general radial equation as it applies to sphere a applied centripetal force induced centrifugal force m were r is the radius since the string joining the spheres is not changing in length then m will be equal to zero and so the centrifugal force outwards on sphere a will be equal to the centripetal force inwards on sphere a which is given by tension t hence t mv r which equals both the centrifugal force and the centripetal force every force acting on sphere a will have an equal and opposite force acting on sphere b hence the centripetal force t acting on sphere b could be considered as a reactive centrifugal force from the perspective of sphere a this example is ok but because it is circular it masks the general picture if you were to choose an elliptical example that would eliminate some of the equalities and also eliminate any confusion that might ensue from those equalities that's why i favour a more complicated example such as a keplerian orbit