8,432 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 8 months
seen 8 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
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 :)
Mar
10
comment If there are 4 dimensions, shouldn't objects appear and disappear in 3D space?
If you want to understand this stuff, I highly recommend Sam Lilley, "Discovering Relativity for yourself".
Mar
10
comment If there are 4 dimensions, shouldn't objects appear and disappear in 3D space?
1) Time is a physical dimension (actually imaginary time is). 2&3) Physical objects can only move up to 45 degrees out of parallel with the 3 space dimensions (that's the speed of light).
Mar
5
comment What is the top speed of the SR-72 aircraft? What affects would traveling at this speed have on the human body?
+ And the ISS folks step outside all the time.
Mar
2
comment Why does deflating baloon spurting through the air make circular motion?
Good answer. I would only add what every teenage rocket engineer knows - a rocket has to pass the "swing test" where you tie it to a string, at its center balance point, and swing it around you in a circle. It has a center of gravity (CG), and an aerodynamic center. The CG has to be forward of the aerodynamic center, or it will want to turn around and go backwards. If that happens under power, it will act just like your balloon :)
Feb
27
comment What happens during gravitational collapse to cause the formation of a star?
My understanding of the fusion reaction is that the caloric density is actually quite low, like a compost pile. It's just that there's so much of it.
Feb
16
comment Why does it take so long to get to the ISS?
@Dewi: The plane of any satellite's orbit is stationary, while the launch site is traveling east, so it is under the orbit twice a day, if the orbit is sufficiently inclined.
Feb
13
comment Can I tell where a leak is in a vertical water pipe based on the water pressure at the bottom?
@Skywalker answer is right. You can only get the height of the water. You can only get the height of the leak if you let the water drain down to it. So if you measure the pressure at the bottom, you need to wait until it stops falling. Actually, that will be an asymptote. It will slow down before it gets there. Actually, you might speed it up by letting some water out the bottom.
Feb
13
comment Why does NaCl (aq) conduct electricity but NaCl (s) does not?
and in solid, they are not even ionized.
Feb
13
comment Airfoils contradict the law of the lever?
@Floris answer is right. It's about energy, not force. The drag experienced by a wing is simply lost energy. A lever is a system that does not lose energy.
Feb
8
comment Application of Bernoulli's theorem
If it helps, I think the easiest way to understand Bernoulli is the simplest: to make a fluid accelerate (change speed), you need a difference in pressure. It's just $F = ma$ for fluid.
Feb
7
comment Why does the airflow in the mid-stratosphere of the northern hemisphere rotate FASTER than the earth?
@tpg2114: I appreciate what you're saying. I looked at the simulation, and the entire southern hemisphere has a broad easterly flow, and the equator is all westerly. This makes me doubt the simulation.
Feb
7
comment Why does the airflow in the mid-stratosphere of the northern hemisphere rotate FASTER than the earth?
If air moves toward the east at all, it is moving faster than the earth, if the reference is the earth's surface. But I agree, it is surprising. There's a lot about that simulation I don't understand. It seems to disagree with what I thought was basic circulation of air on the earth.
Feb
4
comment The stability of falling through a planet
As @docscience said, it looks like harmonic motion, because the gravitational force on you would be proportional to $r$. Basically the shell above you cancels out, leaving only what's below you. The mass of that goes as $r^3$, but the denominator goes as $r^2$, leaving the force proportional to $r$.
Feb
4
comment The stability of falling through a planet
Don't forget coriolis force. Unless you are at one of the poles, you are traveling toward the East at a high rate of speed, but at the center of the Earth you would not be, so on the way down, there would be a lot of rubbing. The gravity at the center of the Earth is actually zero. What you feel at the ocean bottom is not higher gravity, it is lower. What you feel is because you are holding up all the water above you.
Feb
2
comment Can a nuclear reactor be used as a space-based weapon?
@Sofia: You're right, of course. That's no fun at all. I was just reacting to the Hollywood-style depiction of things blowing up :)
Feb
2
comment Can a nuclear reactor be used as a space-based weapon?
Nuclear reactors are slow-motion things. To make a nuclear explosion requires very careful design so that neutrons and other radiation that is generated is caught in just the right way to as to amplify the rate of the reaction.
Feb
2
comment Why are radians more natural than any other angle unit?
@supercat: I remember a debate some time back that would change the convention from 360 degrees to 400. That would have made it easier on aviators, who have to mentally calculate things like: "Given your current heading is $\alpha$, what heading would you turn to to make a 180 degree turn?" It's not the kind of thing where you want to make a mistake. Fortunately, if they have the presence of mind, they can just read it off their gyro-compass card.
Jan
28
comment Does Newton's 3rd Law apply to friction?
Newton's 3rd law says you can't push on something without its pushing back. Friction or not, it doesn't matter.