So simple:
Will this sail-based moving system work? Why?
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2$\begingroup$ You do not have a lot of information to explain your picture. I will say, however, that a sail does not work (usually) by having air push on it. Sails generally act as an airfoil so that air moves around it. $\endgroup$– SeanCommented Nov 25, 2014 at 12:52
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$\begingroup$ Assume you have made it. what will happen ? move ? stop? what? $\endgroup$– AHBCommented Nov 25, 2014 at 13:01
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$\begingroup$ @Sean great point about the aerofoil nature of the sail... all sorts of interesting possibilities for making a vehicle like that work with fan in different place.... $\endgroup$– tomCommented Nov 25, 2014 at 13:03
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$\begingroup$ This is a beginner question. I don't see anything worthy of a down vote. Most beginners want to know about the basic principle instead of how sails really work. If the fan starts air moving and the sails stops the air, the cart would not move. When the sail stops air, a force is created in one direction. When the fan starts air moving, a force just as big is created in the other direction. The two forces cancel. $\endgroup$– mmesser314Commented Nov 25, 2014 at 14:14
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1$\begingroup$ possible duplicate of Blowing your own sail? $\endgroup$– JimCommented Nov 25, 2014 at 14:21
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1 Answer
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It does work - poorly. The sail has to be large enough, and it takes a very strong fan. You would be be better off turning the fan and using it to propel your boat directly as they do on swamp boats in Louisiana.
Proof: Mythbusters video.
The boat will actually move forwards if you have a strong enough fan and a big enough sail.
Imagine that instead of a sail you put your fan at one end of a pipe. With a straight pipe, you point the pipe off the back of the boat so that the fan blows air through the pipe and out the back (fan in the pipe at the fron of the boat.) This will push your boat forwards.
Now put a 90 degree bend in the pipe. The fan sticks off to the side of the boat, but the boat still moves forwards because the air leaving the end of the pipe moves away from the back of the boat.
Now make a 180 degree bend in the pipe. The boat will still move, as long as the inlet and outlet are far enough apart that the outlet isn't sucked back in the inlet.
The U-shaped pipe is like the sail. It reverses the direction of airflow, and if the flow from the fan and from the sail don't interfere with each other too much, the boat will move.
