V V V
W --- cos [phi] and W --- sin [phi] is W --- sec. lb., (3)
g g g
acting along OO´, and so is unaltered.
But the change of the resultant momentum F of the medium as well as of
the body from the vector OF to O´F´ requires an impulse couple,
tending to increase the angle FOO´, of magnitude, in sec. foot-pounds