Would this work?

[Ringo]

Imagine I'm sitting in a sailboat, and have a battery operated fan. I point the fan at the sails - will the boat move forward? What if the fan has an external power source?

Is that like pulling yourself up with your own shoelaces?

[Sephus]

[ QUOTE ]

Imagine I'm sitting in a sailboat, and have a battery operated fan. I point the fan at the sails - will the boat move forward? What if the fan has an external power source?

Is that like pulling yourself up with your own shoelaces?

[/ QUOTE ]

it wouldn't work. the fan would push you backward more than forward. if you turned the fan around and pointed it behind you (like a fanboat) i think it would help you a bit.

[billygrippo]

the fan would make an equal amount of force in the opposite direction.

[hitch1978]

[ QUOTE ]

Is that like pulling yourself up with your own shoelaces?

[/ QUOTE ]

Yes.

[mbillie1]

lol perpetualmotionaments

[eviljeff]

http://archiveserver.twoplustwo.com/ubbthreads.php/ubb/showflat/Number/3919727/page/0/fpart/1

[DanielM]

Actually, it would work. There is force being generated on both sides of the fan, but on one side the sail is catching it, on the other side only minor air turbulence is there to resist the force.

[billygrippo]

[ QUOTE ]
Actually, it would work.

[/ QUOTE ]

incorrect

[stormstarter28]

Question: how are you getting internet access if you're stranded on a sailboat?

[Sephus]

[ QUOTE ]
Actually, it would work. There is force being generated on both sides of the fan, but on one side the sail is catching it, on the other side only minor air turbulence is there to resist the force.

[/ QUOTE ]

the fan is pushing the air forward. you're pushing the fan forward. the boat is pushing the bottoms of your feet forward. you're pushing the boat backward just as hard as the fan is pushing forward on the air. that's how you stay on the boat (see: newton's 3rd law of motion).

so in order to have a net forward force, the air has to push on the sail harder than the fan is pushing on the air. you're never going to get 100% of that kinetic energy from the fan to the air back into the sail.

the boat is going backwards.

[kevin017]

i read through that whole airplane thread, huge waste of time IMO. the answer was clearly that the plane can't possibly take off given the conditions, and it took 15 pages of posts before OP finally clarified that the plane only takes off if you bend the conditions.

[ChrisV]

Sephus has won this thread.

[AquaSwing]

[ QUOTE ]
Question: how are you getting internet access if you're stranded on a sailboat?

[/ QUOTE ]
At least he didn't ask OOT.

Stick the fan in the water like a propeller. Then you're set for home!

[billygrippo]

[ QUOTE ]


Stick the fan in the water like a propeller. Then you're set for home!

[/ QUOTE ]

INCORRECT!1

[DanielM]

[ QUOTE ]
[ QUOTE ]
Actually, it would work. There is force being generated on both sides of the fan, but on one side the sail is catching it, on the other side only minor air turbulence is there to resist the force.

[/ QUOTE ]

the fan is pushing the air forward. you're pushing the fan forward. the boat is pushing the bottoms of your feet forward. you're pushing the boat backward just as hard as the fan is pushing forward on the air. that's how you stay on the boat (see: newton's 3rd law of motion).

so in order to have a net forward force, the air has to push on the sail harder than the fan is pushing on the air. you're never going to get 100% of that kinetic energy from the fan to the air back into the sail.

the boat is going backwards.

[/ QUOTE ]

You're overthinking this. A car on blocks (the wheels aren't touching the road) with speedometer at 10 mph is using about the same amount of energy as one driving on the road with the speedometer at 10 mph. The car on blocks isn't moving forward because there is no friction between the road and wheels to turn that energy into usable mechanical force.

It's not just about how much force there is, it's also a question if the force is being captured efficently. The sail is doing a much better job of capturing the force, so you move forward.

The question being posed isn't about basic physics, it's about engineering.

[kerowo]

[ QUOTE ]
[ QUOTE ]
the boat is going backwards.

[/ QUOTE ]

You're overthinking this. A car on blocks (the wheels aren't touching the road) with speedometer at 10 mph is using about the same amount of energy as one driving on the road with the speedometer at 10 mph. The car on blocks isn't moving forward because there is no friction between the road and wheels to turn that energy into usable mechanical force.

It's not just about how much force there is, it's also a question if the force is being captured efficently. The sail is doing a much better job of capturing the force, so you move forward.

The question being posed isn't about basic physics, it's about engineering.

[/ QUOTE ]

The sail isn't going to be 100% efficient, so all it's going to do is slow down your backwards motion.

[Sephus]

it sort of looks like you think the fan is blowing in both directions.

it's not a question of sail vs. "air turbulence," it's a question of sail vs. fan blades.

[hitch1978]

[ QUOTE ]

You're overthinking this. A car on blocks (the wheels aren't touching the road) with speedometer at 10 mph is using about the same amount of energy as one driving on the road with the speedometer at 10 mph. The car on blocks isn't moving forward because there is no friction between the road and wheels to turn that energy into usable mechanical force.

It's not just about how much force there is, it's also a question if the force is being captured efficently. The sail is doing a much better job of capturing the force, so you move forward.

The question being posed isn't about basic physics, it's about engineering.

[/ QUOTE ]

So the car is using the same energy without the road friction as with it? Nice.