Post by Steve HayesPost by LionelEdwardsFarting is different to blowing, in that the potential
energy has already been created chemically, so Newton's
law doesn't apply. After discussing it with the
duck nephews, I think we agree that any moving air can
power a sailboat, so blowing into a sail might have some
merit. Probably slightly more use than pissing into
the wind?
But if you blew into a sail, you would have to be doing so from
somewhere outside the boat. If you were standing in the boat the
energy received by the sail would be counteracted by the energy
transmitted to the boat by your feet.
I think the answer is that yes, you could make the sailboat move forward
by blowing air onto the sail. Here's my reasoning:
A sailboat does not need to be travelling downwind in order to have the
sails propel it. Assume we are sitting on the gunnel, pointing a big fan
directly toward the other side of the boat. If the mainsail is sheeted
in at, say a 45 degree angle to the fore/aft axis of the boat, there
will be a deflection of the air toward the stern, in exactly the same
manner as if the prevailing wind were blowing in the same direction.
This would cause the boat to move forward, just as the wind would.
Any energy transmitted to your feet/bum will indeed be applied to the
boat, but at an angle that will only apply in a direction toward the
windward side of the boat. That energy will have a very small effect of
the boat's direction, for two reasons:
1. The mass of the air being pushed is very small compared to the weight
of the boat and the fan holder.
2. The keel of the boat will further decrease any windward movement,
just as the keel prevents the boat from moving straight downwind with
the geometry specified. The hull will also have the same effect as the keel.
The net result is that, IMO, the overall effect will not be much
different than if a wind was being provided externally to the boat.
--
Which odd number becomes even if you take away a letter?
(S)even.