You've got the right answer here, but don't realize that it contradicts the kids statement. Given my bike statement, and your rollers, and if we use a perfect coupling to the roller and tires when I hit my front brake..... I would be ROTATED over the bars. Rear brake would result in driving the front tire down through the earth. Think about this JB - in real life, you hit the brakes, and your arms stiffen up due to the momentum of your body being coupled to the bike. There would be a small rotational element too, but insignificant to inertia. If anything, in the roller scenario, I'd feel a kick in the butt and a pull on my hands as the bike lifted me up and over. So do you have a video of your device GDWFTTW in a wind tunnel? You could shut us all up here and now if you do...
Your device is not powered by the wind. It is powered by the treadmill. The wind it develops is a result of that power input, and it is enough to overcome the rolling resistance of the wheels. Again, go find a wind tunnel. Or even simpler, go out on a windy day, find an empty stretch of road, get your device and a balloon (not helium filled) and release them together. If the device can outpace the balloon, then you can shut us up. ETA: let's help you out here. Since there will be some inertial resistance to your device getting up to speed, and the balloon won't, when you release the balloon, run alongside with your vehicle to match the speed of the balloon. Then release the car and see if it keeps up with the balloon. the balloon will be going slower than the wind, but your car won't be able to keep up with it........
Yes, and on the other end of that equation is the prop -- and the wind can "couple into the vehicle whatever is needed (within the limits of the diameter and L/D ratio of the prop). It truly is the same as the age old "when you pull on a rope tied to a tree -- who's keeping the rope tight? ... you or the tree?" Nope -- if you put the motor directly on the wheels, you no longer have to deal with the aero limits of the prop. If you put the motor on the prop, you no longer have to deal with the friction limits of the wheels. If you let the wind blow relative to the rolling surface, you must deal with both. Wayne, you are ignoring the answer to the sailboat question: "What powers a sailboat -- wind or water?" Surely we don't have a disagreement on this one do we? If so, let's chat about it. JB
Hi haroki. It's powered by the differential movement between two mediums. If I put it in the wind tunnel, it's the electric motor moving the air and creating that differential. If I put it on the treadmill, it's the motor moving the rolling surface creating that differential If I put it on the street, it's the power of the sun moving the air and creating that differential. JB
Let's see it then!! Or better yet, instead of the street, which will induce too much rolling resistance, go to an indoor basketball court and use a fan, or fans. You up for a challenge?
Yes I am. Here is our entry into the MythBusters Video challenge. http://www.youtube.com/watch?v=4GOlSi-2p3g JB
You didn't see the problem with the remote steered vehicle at the beginning? The flag, which was used to show that the vehicle was going faster than the wind, was directly behind the prop. Hence, by placing it in the correct place, it was "seeing" prop wash. This in no way shows that it was moving faster than the ambient wind. Again, if they would have released a balloon next to the vehicle as it was traveling, or had the flag out of the prop wash, it could be considered a valid test. What happened to you JB? You're starting to sound like the "run your car on water" guys..... Prepare to be busted........
You'll have to explain the "problem" with the remote steering. Nope -- from the side it was filmed you just couldn't see that there is a long stick holding the streamer out to the *side* (other side from the camera). The streamer is no where near the camera. Find the enitire video of the outdoor cart on Youtube and you can see the side mounted streamer several times. We certainly agree on this point -- that's the way to prove the point to the average person. To someone knowledgable in physics, the treadmill is the most accurate and controllable way. And since the flag *was* out of the prop wash, therefore valid. LOL -- I'm the same skeptic I ever was ... I also know the real deal when I see it. There's no violation of any laws going on here. I would love to see them pick it up, but as with any TV show they have a million yahoos slinging ideas -- the chances of using one of mine aren't very high. JB
1-Yes I know that. It was a trick question to see if you could explain why the streamer, at times, was blowing towards the front of cart, and why the video was cut part way in, right when the streamer was like that. Look, I understand that a breeze passing through the prop will cause it to spin, which will in turn power the drive wheels, and if the gearing is correct, the cart will briefly be able to go faster than the wind when the wind dips briefly in velocity,since the spinning prop will store a lot of kinetic energy, giving the illusion that it can go DWFTTW, steady state, with a little creative video editing. The wind is your power source. There MUST be wind blowing through the prop in order to supply power to the drive wheels. As the cart nears wind velocity, there will be no more power source, since the net flow through the prop is zero. This is what is seen in that video. That is why the streamer can be seen, at times, to be blowing towards the front of the cart. The cart is VERY efficient at going down wind, but it cannot go faster than the wind - STEADY STATE - it can only do this for brief periods when the breeze slackens and kinetic energy is powering the cart. 2- I find this an interesting statement, since you didn't recognize the curve ball I threw you with my bike/rollers vs chevy/treadmill comparison. They are not the same experiment. Of course you are correct that you will be slammed into your seatbelts when you slam on the brakes whie on the treadmill - you will be spit off the back. And once again, the treadmill is not the correct way to demonstrate DWFTTW. The thrust the prop develops is a result of the power input from the wheels. You set it on the treadmill, and once the prop spins fast enough to develop more thrust than is lost due to rolling resistance and power transmission losses, of course it can advance. I gave you the real way to prove DWFTTW - namely, put the cart in a windtunnel, where the windspeed can be both measured and controlled to maintain steady state, and put the cart on rollers, measuring the distance/speed that the wheels would be covering in the real world. This eliminates the variances in wind speed that are a natural occurence in nature. This would be proof. ----- But since you claim to understand the physics, explain exactly HOW the physics work that enable this. Videos don't cut it.
After thinking about it some more, the roller experiment is all wrong. The difference between the cart and the wind will remain constant, so the wheel speed/traveled can be geared up to meet whatever criteria you choose. You would need a wind tunnel still, but you'd need to let it roll, which means you'd need a very long wind tunnel. So that's out. What the cart depends on is NOT the difference between the wind speed and the ground, except at a standstill. What it depends on is a difference in windspeed between it and the cart. Once the cart reaches the wind velocity minus rolling resistance, there is no more power source to be tapped. So that makes it a free energy device.........