7,415 reputation
1628
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 1 month
seen 4 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.


Aug
23
comment Airplane on a treadmill
The simplest way to answer this is to imagine replacing the wheels with frictionless skates (after all, that's what wheels are trying to be). Then you see that the premise of the question is not possible. Except for the implied drag due to spinning up the wheels, There's no speed the ground can be moving backward that prevents the plane from moving forward.
Aug
18
comment Calculate flow rate of air through a pressurized hole
The answer is right. Intuitively, if you want to double the velocity of the escaping air, you need to quadruple the pressure. The reason is that pressure (force) is momentum (of the air) per unit time, and if the velocity doubles, you're doubling the momentum of each parcel of air, and you're doubling the number of parcels of air.
Aug
18
comment Would a three wheeled vehicle be faster than a four wheeled vehicle of the same weight?
@Ben: It certainly does. The car starts with a certain amount of potential energy. At the end its kinetic energy consists of kinetic energy due to forward motion plus rotational kinetic energy of the wheels. The more rotational energy there is in the wheels, the less there is in forward motion. You could look at it as - the necessity to spin up the wheels acts as a drag on the car. The only possible effect of 3 instead of 4 wheels is fewer wheels to have rotational kinetic energy.
Aug
15
comment Calculate flow rate of air through a pressurized hole
It has a strong dependency on the shape of the orifice. Check this out: Flow through an orifice
Aug
13
comment Why is the range for a particle thrown at 90 degree same as that of a particle thrown at 0 degree?
What is the angle measured against? The ground? What is the velocity of the projectile? How high above the ground is it when it is thrown? The question is still not clear.
Aug
12
comment Pressure at a bend in a pipe
A way to think about it is a water slide having curves. Obviously the water will rise up on the outside of each curve (as will the child enjoying the ride). Another thought: isn't this the way those infamous gas centrifuges work?
Aug
10
comment Water pump with a tap connected at its opening not pumping water when water is drawn from the pump before starting the pump
It sounds like the pump needs water in it to run, so it needs to be "primed". People turn on the tap, drain the upper tank, and when that's empty, drain the pump. It sounds to me like the T joint needs to be at a higher elevation, above the pump.
Aug
6
comment How is viscosity described on the molecular level?
I like your train analogies.
Aug
6
comment How is viscosity described on the molecular level?
Elasticity in a gas is not a matter of attraction and repulsion, it is a matter of continual thermodynamic collisions. For viscosity, all the answers are good.
Aug
5
comment What does centre of lift depend on?
@Jan: That part doesn't bother me - off the cuff, it's where there's the greatest curvature of flow. Anyway, as I said, I think it's a good question.
Aug
5
comment What does centre of lift depend on?
@Jan: The part of your question I'm not sure I can answer is - what produces the upwash? Could it be the lower pressure above the wing drawing the leading air up?
Aug
5
comment What does centre of lift depend on?
It's a good question. I like this source. The program he uses to calculate flow about an airfoil should give the answer.
Jul
31
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.
Jul
29
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.
Jul
29
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.