8,422 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 8 months
seen 6 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.


Mar
26
comment Is Magnus effect a corollary of Bernoulli principle?
It's not energy conservation along a streamline. It's momentum conservation along a streamline. It's $F=ma$, which is momentum conservation.
Mar
26
comment Why does a propeller suck in air from the front?
I bet your question comes from the standard wrong explanation of how wings work, the explanation that fails to account for downwash. Let me direct you to my favorite site for explaining how wings work.
Mar
21
comment How can a petrol car require less fuel at 55mph than a lower speed at the same rpm?
Just drive the car in first gear for an hour, it doesn't need much gas, but it doesn't go many miles either, so the miles per gallon is low
Mar
19
comment Is Physics being formally documented somewhere?
Actually, if there were a centralized database of physics knowledge of "immutable concepts", it would be a great resource for me and others who like to show where some such concepts are wrong :)
Mar
18
comment How much power can support an object to float in the air near the surface of the earth?
Go with @akhmeteli answer.
Mar
18
comment How much power can support an object to float in the air near the surface of the earth?
How near the surface? If the surface is really flat, like a polished granite table, and if the weight rests on a plenum of wide area, with a 1-micron gap around the edge, then it will take very little energy. The only energy it would need is to keep up some pressure to replace the bit of air that escapes.
Mar
17
comment How does Hendo hoverboards achieve the self-propelling motion? What is the MFA?
You're confused - about the difference between electrostatic repulsion and magnetic repulsion. They are not at all the same thing. The voltage necessary to produce this amount of electrostatic repulsion would be far more than any reasonable amount of insulator could resist, and the rider's hair would be standing on end, not to mention lightning.
Mar
16
comment How pressure effects on the time that a toy hovercraft hovers?
From what little I've thought about this, and the discussions below, I'm guessing the bottom surface of the puck could be dished somewhat. It's not necessary, or maybe even desirable, for the air layer to be the same thickness throughout. The thickness that matters is where the air escapes to the outside, at the rim. (Real hovercraft have a "skirt" around the edge.)
Mar
15
comment How pressure effects on the time that a toy hovercraft hovers?
OK, the OP made it clearer what the situation is. It looks to me like the main pressure drop is in that thin film from center to edge. I would suppose it is mainly viscous, but the velocity would have to decrease with radius (assuming a flat bottom surface), so I'm back to square 1 :)
Mar
15
comment How pressure effects on the time that a toy hovercraft hovers?
That's for viscous laminar flow in a tube. Flow through an orifice with a pressure drop is different. There, if you double the velocity, you double the momentum change per parcel of air, but you also double the number of parcels. (Density change does not enter, as long as the Mach number is low.)
Mar
15
comment How pressure effects on the time that a toy hovercraft hovers?
Pressure proportional to flow rate? Usually pressure goes as flow-rate squared (at low velocity). Like in an airplane - double the speed, quadruple the lift.
Mar
15
comment How pressure effects on the time that a toy hovercraft hovers?
A hovercraft with a balloon? It's unclear what you are talking about.
Mar
14
comment In a dust cloud around a star, what causes bodies to form?
Do you suppose the clumping charge could come from Van de Graaff action?
Mar
14
comment In a dust cloud around a star, what causes bodies to form?
@CoilKid: I wonder if clouds that are otherwise neutral become charged just by flowing past each other, the same way charges build up in a thundercloud or a volcano cloud (Van de Graaf generator), and if that could provide the charge necessary to form clumps.
Mar
14
comment In a dust cloud around a star, what causes bodies to form?
Is it possible that the formation of polar molecules like water naturally want to clump, even though they are overall neutral? I'm thinking of "dirty snowballs" (like I have out my window :)
Mar
14
comment In a dust cloud around a star, what causes bodies to form?
I hadn't thought of Van der Waals force. That's interesting.
Mar
14
comment A cup of water in ZERO gravity
@user3932000: No, there's really no such thing as zero gravity, unless you go far out in the universe, far away from any galaxies, etc. Aboard the ISS, there's plenty of gravity. The whole structure and everything in it is falling toward the earth. It just happens to be going so fast horizontally that as fast as it falls, the surface of the earth bends away because it's curved, so the ISS never gets any closer to the ground. They call it "micro gravity", but all that means is everything is falling together at the same time.
Mar
14
comment In a dust cloud around a star, what causes bodies to form?
OK, that's a big help. I wonder if it extends to planetary dust clouds. I mean, we see things like comets. I wonder how they are formed. Rather than, say, disintegrated?
Mar
14
comment A cup of water in ZERO gravity
@user3932000: You don't have to be in space to be in a zero-gravity environment. In fact, a less confusing term is "free fall". It can be easily done in an aircraft.
Mar
14
comment A cup of water in ZERO gravity
It's easy to create a zero-gravity environment. Just toss the cup of water in the air. Then while it's in the air, just grab the cup away from the water. My son once asked me how things can float in space. I just demonstrated with car keys. I tossed them up and followed them with my hand. They "floated" above my hand :)