6,947 reputation
1424
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 2 years, 10 months
seen 3 hours ago

BS Mechanical Engr.
PhD CS(AI)
CS Prof (4yr)
Numerous consulting jobs.
15 yr at http://www.pharsight.com
Published book on CS & several articles
4 kids, 2 grand
Pilot(student)

P.S. The picture is a Beta-prime distribution. It shows the program speedup factors you can get if you see a problem twice in 2, 3, 4, and 5 samples.


8h
comment Airplane on a treadmill
@MarkBiwojno: John is right. What matters to an airplane is air, not ground. A Cessna 172 requires air to be traveling past the wing at about 55 nautical miles per hour. The wing deflects the air downward, creating more lift than the plane weighs, so it takes off. The ground can be going forward, backward, sideways, whatever. What matters is the motion of air over the wing. The propeller creates thrust against air, to accelerate the aircraft. The wheels, skids, floats, are only there to hold it up when it's not supported by the air.
2d
comment From where comes the raindrop
The cloud and the raindrop are carried by the mass of air, except that the raindrops fall because they are bigger and heavier than cloud droplets. They just do what the air tells them to do.
2d
comment Erosion effect from Coriolis force in a South-to-North water channel?
I agree with your instinct that those sides would experience wear, and of course the flow rate would matter. I would expect the effect to be least at the equator, and greatest near the poles.
Jul
22
comment Is a falling, perfect sheet of fluid possible to create?
This would be a good experiment to try in micro-gravity. I think the only significant force would be surface tension, which you could minimize by a) making it large, or b) making it soapy :), or c) putting a solid ring around it.
Jul
18
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
You could just have a stationary scaffold around the entire black hole, and stand on that.
Jul
17
comment Add weight in front or behind the moving wheel?
@user55493: I see kids do it all the time. They go up-hill on their skateboards in a series of S-turns. Each curve of the S-turn, they are pushing sideways. It doesn't matter how many wheels they do it on, or whether their weight is forward or back. What matters is the sideways push.
Jul
14
comment Does the Higgs boson give mass to ALL other particles?
Is it possible that the mass of nucleons is mostly the energy (over $c^2$) of the binding of their components, and not really anything to do with the Higgs field?
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: It's a great question you asked. In my pilot training, I was taught to be very aware of "wake turbulence" - those invisible vortices coming off heavy-plane wingtips.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: I just googled "vortex merging" and a ton of high-quality stuff turned up!
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Now I'm the one who's skeptical :) Any vortex has to have a central region of low pressure, so that the pressure gradient provides the radial acceleration keeping it circular, so when the vortices come close together, the pressure gradients have to superimpose, affecting the paths of particles. But the trouble is, if that were the only effect, then counterrotating vortices would also merge. Hmmm...
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS: Well, as I said, when they come close together there will be counter-rotation between them. This will divert flow from each vortex to the other. If you're after a mathematical description of this process, maybe you should research it or better yet, construct it. For the other case, counter-rotating vortices, they don't merge because the physics are obvious, as Floris pointed out.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Then check Floris' answer. It's a simple matter of conservation of vorticity (i.e. angular momentum), and kinetic energy.
Jul
14
comment Why do co-rotating vortices coalesce, but not counter-rotating ones?
@BrysonS. Forget subsumption. They simply merge, because each little parcel of air follows a path.
Jul
11
comment Computing the force generated by a sail on a boat
@T.Kiley: I'm afraid you need to know how the sail functions as an airfoil - namely what is its chord, its angle of attack, and its coefficients of lift and drag as a function of those.
Jul
11
comment How effective is speeding?
It's more important to minimize time spent going slow than to go fast.
Jul
9
comment Problem understanding basic sail mechanics
+1 @T.Kiley: Don't confuse yourself with the Bernoulli kerfuffle. Just consider the centerboard of the boat as if it were a skate. Consider the sail as if it were a knife blade, and the air were jello. Then satisfy yourself that no matter how fast the boat is sailing downwind, there is a sail angle that can give it forward thrust. A simple physical analogy is a wet watermellon seed squeezed between thumb and forefinger. Here's a similar question.
Jul
3
comment Do airlocks in space decompress violently as they do in movies?
For the airlock, it depends how suddenly the air is released. People consist of lots of muscle, fat, bones, etc. plus liquid plasma in fairly strong tubes, plus air in lungs. If they don't try to hold their breath, there's not much to decompress.
Jul
3
comment How should I throttle my rocket to reach highest altitude?
Here is a *very worthwhile read: *
Jul
2
comment Paper airplane physics
@J...: The OP had some basic misconceptions that needed to be corrected. When that is done, the equations just fall out. I was trying to correct the misconceptions.
Jun
30
comment What does a wing do that an engine can't?
There are misconceptions in some of the answers here. Lift/Drag ratio is beside the point. Angle of the engine axis is beside the point. Gliders vs. rockets are beside the point. Falling plates are beside the point. The answers that are on point are the ones that talk about momentum vs. energy of the downwash.