8,024 reputation
1728
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 6 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.


3h
comment Roughness of the Surface and the time that a toy hovercraft hovers?
When you say "hovercraft" you mean something that floats on a cushion of air within millimeters of the floor or whatever it is hovering on, right? Then it all depends on the seal around the edges. The more air that gets out, the more power it takes to refill the air cushion, so the shorter the battery life.
3h
comment Will 3-D printing on the nanoscale ever be possible?
Replicate an iPad in a few days? Of course it's theoretically possible - a small matter of engineering and a billion or so $. Harness some designer-RNA, and maybe a world-wide attack from martians to give us some incentive. Of course, there are quicker ways to make iPads.
8h
comment Does a force being applied in an ideal case to an object of infinite mass where there is no friction always result in an acceleration?
$F=ma$ so $m=F/a$. You can talk about infinities and zero-divide if you like. Seems a little silly.
2d
comment Since Earth spins, would an aircraft travelling opposite to direction of Earth spin take less time?
When I hear "why or why not" my homework-detector goes off. Regardless, if you can fly above the atmosphere and fly west toward that point, you will get to it sooner because it is moving east. Of course, if it's on the equator, you could simply get above the atmosphere and wait 12 hours, and it will come to you (though that means you are traveling west with respect to the earth at about 1000 mph). Anyway, if you're flying in air, which is basically attached to the earth, the spin of the earth makes no difference. It's just a matter of wind.
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
19
revised Coriolis force on bullet vs airplane
added 655 characters in body
Mar
18
revised Coriolis force on bullet vs airplane
deleted 372 characters in body
Mar
18
answered Coriolis force on bullet vs airplane
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?