Stephen A. Lawrence wrote: > > > Harry Veeder wrote: >> I would like to reconsider the tubular lifter experiment which I mentioned >> last week. >> >> The upper positive wire produces a positive ion cloud beneath so they repel >> each other. If I have understood the EHD account correctly, the force of >> repulsion is predicted to be greater than the force of attraction between >> the upper positive wire and the lower negative tube. As a result there is a >> net force upwards and the lifter rises. The tendency of the lower negative >> tube to be pulled upwards does not contribute to the net upwards force. >> >> Now, when the lifter is stationary the tube will be elevated by its >> attraction to the positive wire and ions. However, as seen on the video even >> as the lifter accelerates the tube remains elevated. While this is >> happening, the structural design of this particular lifter makes it >> logically impossible for the upper wire to be credited with lifting all the >> components. Based on that premise a force analysis will end in circular >> reasoning. Therefore the lower tube must be credited with all or at least >> some of the lifting force. This is inconsistent with EHD theory. > > This _sounds_ remarkably like some of the weird things you can do with > the Bernoulli effect. Have you ever tried to blow a ping pong ball out > of a funnel, by blowing in through the point of the funnel? If you > start blowing with the funnel "upright", with the ball just held in by > gravity, and you have enough lung power, you can actually turn it upside > down and as long as you keep blowing, the ping pong ball will "stick" > until you stop blowing. (Experiment last tried in Junior High School, > so don't press me on the details!)
The coanda effect? > A breeze from the wire to the tube, passing around the tube, could very > well exert a pull on the tube, rather than a push, as you might have > expected. (It all depends on the direction the air flow takes once it > "breaks away" from the surface -- if it goes part way around the tube > and breaks away while heading down, conservation of momentum says the > force on the tube is up, not down. But Bernoulli must enter the game to > explain how that could possibly work.) In theory this phenomena eliminates the logical problem, but in reality is the air moving fast enough over the tube to actually lift the tube? How would you test this? > It is often very difficult to "see" which item is being "pushed on" when > thrust is exerted on gas. A ram jet is another wonderful example > (though unrelated to the Bernoulli effect, AFAIK) -- the air comes in > the front, accelerates, and goes out the back, so the engine develops > thrust -- but unlike a turbofan there's nothing /obvious/ for the air to > "push against". At first glance it seems like it can't possibly work. Harry
