6,281 reputation
1322
bio website en.wikipedia.org/wiki/…
location United States
age 69
visits member for 2 years, 7 months
seen yesterday

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.


May
11
comment Find drag force on link of rotating chain
I was not able to view the video, and I assumed the chain was fastened in the center and was being swung around. I just noticed you said a closed chain. Is the chain in the shape of a circle, spinning like the rim of a wheel? If so, I need to change my answer.
May
8
comment What's the reason for the seasons?
Your diagram is slightly wrong. The white ellipse with the arrow on it, representing the rotation of the Earth, should be tilted to the right by 23 degrees so it is perpendicular to the north-south axis. And there is a big temperature difference between day and night - we just don't call it seasons.
May
7
comment Why is exhaling more forceful than inhaling?
That's what I was going to say, for the same reason the flow around a fan is not symmetric fore and aft. Going into the fan it is simply being drawn from all directions, but coming out of the fan it has momentum in one direction, so forms a jet.
Apr
30
comment Is this really how a capacitor works? Why doesn't it behave like a resistor?
@jak: Yes. Conductors are always full of charge, just like water in a pipe. We only say the capacitor is "charged" when enough of the carriers have been moved to one plate, and the lack of them has been moved to the other, making them want to get back, and that "wanting" is the voltage.
Apr
30
comment Is this really how a capacitor works? Why doesn't it behave like a resistor?
@jak: You can always fall back on a hydraulic analogy. Think of a capacitor inserted in a wire as a springy diaphram inserted in a water pipe. In your case, you have two of them, that's all.
Apr
30
comment Is this really how a capacitor works? Why doesn't it behave like a resistor?
@jak: That's right. The air doesn't stop the potential from being felt across the gap, and if the plates were really really large, current could flow for quite a long while before it slowed down and stopped.
Apr
30
comment Is this really how a capacitor works? Why doesn't it behave like a resistor?
@jak: That's the same as asking how does current flow into a single capacitor, or even how does current flow in a conductor. It flows in a conductor because there is a potential gradient that pulls the charge carriers. In a capacitor, the potential gradient is transmitted across the gap. An open switch is just a capacitor with very small capacitance.
Apr
30
comment Looking for a way to simplify a physics formula
@Luboš: You're right of course. I only remember, 30 years ago when I taught C.S. at Boston College to undergraduates, who were supposedly the "best and the brightest", and I put $C = (F-32)5/9$ on the board, the fright that arose in the hall. Well, since their parents were paying my salary, I decided the most useful thing to do is address students at the level they are at. So I did some remedial teaching. It wasn't just math either. It was also basic English grammar.
Apr
30
comment Looking for a way to simplify a physics formula
@Luboš: Let's be helpful. She asked an honest question.
Apr
30
comment Looking for a way to simplify a physics formula
Did you try algebra? You can do anything you want, as long as you do it to both sides (except divide by zero). First divide both sides by $1/2$. Then divide both sides by $t^2$. That leaves $a$ all by itself, and what it equals is on the other side.
Apr
26
comment Forces on an airfoil
There's a nice video here showing with bits of yarn what happens when a wing stalls. The pilot reduces power and pulls the nose up to maintain altitude. When the critical angle of attack is reached, the yarn no longer lies flat against the top of the wing.
Apr
26
comment Forces on an airfoil
You can't really distinguish between angle of attack and Bernoulli. The angle of attack causes air to be deflected into a downwash, and that can't happen without a pressure differential, and Bernoulli is just a way of explaining how that pressure differential arises. If the angle of attack is high enough, the flow detaches from the top of the wing & Bernoulli no longer works, so much less downdraft, and that's known as stalling the wing. The critical angle of attack is typically around 19 degrees.
Apr
23
comment Why does the higher pressure of air underneath an aeroplane wing keep it flying?
Check out Stick and Rudder, by Langewiesche. It's a delightful book about aviation, and has been recommended for generations.
Apr
23
comment Why are color values stored as Red, Green, Blue?
@50ndr33: Yes it does, because the red sensor responds to a broad distribution of wavelengths, heaviest in the red. Green, same way. Check this out.
Apr
22
comment Why does the higher pressure of air underneath an aeroplane wing keep it flying?
Have you ever put your hand out of the window of a moving automobile, and angled it upward? The air pushes it up, by making more pressure underneath and more on top. Also because you are deflecting the air downward with your hand. A wing works the same way.
Apr
17
comment Why does a bullet bounce off water?
When I studied fluid dynamics (which I've mostly forgotten) there was something called Reynolds Number, relating inertial to viscous forces.
Apr
17
comment Why does a bullet bounce off water?
@annav: Interesting. As a mechanical engineer & sometime pilot, I was looking at it as a matter of planing - a moving wedge thrusting material downward, but cohesion also has to matter in a fluid (as in dambusters' rotating cylinder). Thanks.
Apr
17
comment Why does a bullet bounce off water?
@annav: Is surface tension a necessary condition for a surface to exist on a liquid?
Apr
4
comment Why is the time taken for something to fall proprtional to acceleration due to gravity?
@Clive: Hey, I'm always on the edge of being in trouble. It's more fun that way. You too.
Apr
4
comment Why is the time taken for something to fall proprtional to acceleration due to gravity?
@Clive: You're right of course, and so is everyone else. When I was 16 (I wasn't always old) I considered myself pretty smart :) So I hope OP would not be derailed by a little challenge.