7,600 reputation
1628
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 2 months
seen 21 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.


Sep
2
comment Circular motion and time dilation
@AlanSE: The time dilation due to velocity alone is relative - each one sees the other as slower (special relativity). The time dilation due to acceleration is absolute - they both agree which one is slower (general relativity). That's how the twin paradox is resolved.
Sep
2
comment Circular motion and time dilation
@Aloewishs: Acceleration is what matters, not velocity. Clocks will run slower in a helicopter at 3km than in a supersonic jet at 30km, and slower yet than in a balloon at 60km altitude.
Aug
29
comment How to find the required inlet velocity/pressure to achieve 0.5 m/s in one part of the underground tunnel?
Sometimes people on this site are a little persnickety. Don't be concerned.
Aug
29
comment How to find the required inlet velocity/pressure to achieve 0.5 m/s in one part of the underground tunnel?
1 meter/second? Is it a simple case of mass conservation, because the velocity is slow enough to be considered incompressible.
Aug
27
comment Why there is a time gap between the news presenter and the field reporter?
@user22180: As I said, I can guess too. But guessing isn't knowing. Somebody knows the answer. I don't.
Aug
27
comment Why there is a time gap between the news presenter and the field reporter?
I was watching such a newscast, and the field reporter actually was listening to a cell phone, and the microphone picked it up. So on the TV the anchor asked Question XYZ? and you could hear the Question XYZ? come from the field reporter's cell phone about a second later. So the field reporter would hear the question sooner if he simply watched the channel! I can guess why, but I really don't know.
Aug
26
comment Flow past a parabolic lamina submerged in a tube. Please see the attached figure
Sorry, I still don't get it. If I turned a parabolic bullet on a lathe and inserted it into a section of PVC pipe, pointed the whole thing vertically, and then poured honey down it, would that be what you're describing?
Aug
26
comment Why do we fall down when the bicycle slows down?
Sure I watched it carefully, and the point of support is always moving, even at 2:0, though not necessarily by a lot. (If there were a groove that the front wheel had to stay in, it wouldn't stay up long.) You're right that she's not steering, but something is, and I assume angular momentum (precession) of the front wheel is at least partially responsible. (I guess I don't see how I'm contradicting myself. :)
Aug
26
comment Why do we fall down when the bicycle slows down?
I'm afraid I'm with Brandon, not so much on the "curved path" idea, but on what is equivalent, which is that the point of support is constantly shifting left or right (which you can see in the video), and at high speed it takes very little steering to do that. At low speed it takes a lot. The bike self-steers by various means (including gyroscopic precession, IMHO). (If the handlebar were clamped so it could not steer, the bike would immediately fall over.)
Aug
26
comment Why do we fall down when the bicycle slows down?
++ That's my take. You're always falling one way or the other, and you're compensating by always moving your point of support to counter your fall. Gyroscopic precession helps you do that, but isn't necessary. There are ski bikes that don't have wheels.
Aug
26
comment Flow past a parabolic lamina submerged in a tube. Please see the attached figure
Are the tube and the parabolic body round, or 2-dimensional? You say the "falling film", which seems to make it ambiguous. Is gravity involved? Is the velocity fast or slow (Reynold's number)>
Aug
25
comment Gravitational acceleration at half Earth's radius
Don't you mean $r/R$ where $R$ is the outer radius of the earth, and $r$ is the radius you are at?
Aug
25
comment How to calculate pressure loss due to water leakage from a hole in a pressurized unit
@Mitchell: If you can measure $V_{air}$ then you can get your expression. A way to do that is to have a closed cylinder of known volume full of air. Then pump a known volume of water into the bottom of it, which compresses the air down to a known volume. Another way is to use a glass tube as a level indicator on the side of the cylinder. Another way is to put the cylinder on a scale, so you can measure how much water went in. No matter how you do it, you need to experiment.
Aug
25
comment How to calculate pressure loss due to water leakage from a hole in a pressurized unit
@Mitchell: You calibrate it. Set it to a pressure $p_1$. Then either measure volume $V_1$ of the air pocket, or let out a certain amount of water $\delta V$ and measure the decrease in pressure $\delta p$. Assuming constant temperature, Boyle's law just says $p_1 V_1 = (p_1 + \delta p)(V_1 + \delta V)$. You can solve for $V_1$ if you want to.
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?