Physics brainteaser

[Turok]

Remember the POAT (plane on a treadmill) thread from a year or so ago? Got another one:

Can a device be built that can travel downwind, faster than the wind, powered only by the wind, steady state?

JB

 

[151]

Sure, battery powered vehicle with a retractable wind powered generator to charge the batteries.

 

[omegapoint]

I believe one of the criteria was powered only by the wind.

 

[Wayne Gibbous]

It can't go faster than the wind, if its travel direction is exactly down wind (parallel to the wind velocity vector).

If it is allowed to travel at a down wind angle, then yes. The wind will travel around the curvature of the sail at a faster rate (Bernoulli's) and essentially "pull" the vessel faster than the downwind velocity.

 

[trendlover]

A sailboat. Ice skates.

 

[Turok]

I have built, and can demonstrate on demand a vehicle which can travel directly downwind, faster than the wind, powered only by the wind, steady state.

http://www.youtube.com/watch?v=Vjt6G8D4x0k

 

[Wayne Gibbous]

Quote from Turok:

I have built, and can demonstrate on demand a vehicle which can travel directly downwind, faster than the wind, powered only by the wind, steady state.

http://www.youtube.com/watch?v=Vjt6G8D4x0k

Nope. I don't buy it.

You are imparting energy, through the wheels and into the prop, from the treadmill. That's not wind power. The fact that it goes faster than the treadmill is not important. You have created an energy transfer from the treadmill motor, not the wind.

Actually blow wind at it, then show it going exactly up wind (or exactly down wind) faster than the wind, with no treadmill. Then patent it!

Maybe I'm just a born skeptic?

 

[Arnie]

Your experiment would imply that your little gizmo produces more energy that is uses. But we already that isn't possible. I think what you have done is turn x revolutions of the wheel into x revolutions of the prop. Similar to the leverage of a pully or lever.

 

[Turok]

Quote from Wayne Gibbous:

Maybe I'm just a born skeptic?

Just know that I consider that to be a very good thing.

Nope. I don't buy it.

You are imparting energy, through the wheels and into the prop, from the treadmill. That's not wind power.

Based on the equivalency of inertial frames of reference,(a longstanding principle of physics since Galileo) we know that the cart on a moving roadway in still air is exactly the same as a cart on a still roadway with a tailwind.

Motion is relative -- there is no "wind" unless measured against something -- usually the ground. If you step onto a long people mover at the airport you will feel a 4mph wind in your face even if you are standing still. Is there wind? How can there be -- it's a enclosed room and still air? Yet you feel it.

How would one answer the question "Is a sailboat wind powered, or water powered?"

Answer: It's both and neither, but certainly not one or the other -- the truth is a sailboat is powered by the relative motion *between the water and the wind*. As long as one or the other is moving, the boat will "see" wind and function normally.

Same with the cart -- is it wind powered or is it 'ground' powered? -- the truth is the cart is powered by the relative motion *between the rolling surface and the wind*. As long as one or the other is moving, the cart will "see" wind and funtion normally.

JB

PS: Nothing to patent -- even this design has been demonstrated several times since the '50s.

 

[Turok]

Quote from Arnie:

Your experiment would imply that your little gizmo produces more energy that is uses.

It doesn't imply that, and we don't imply that. The device is powered by the relative motion between air and rolling surface. Shut off the 'wind' and the device stops.

But we already that isn't possible.

Yes we do.


JB