7,230 reputation
1625
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years
seen 2 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
30
comment Why is there this asymmetry between the two foci of an orbital ellipse?
Well, I don't know, but the same thing happens if you take a planar cut, at an angle, through a cone. The curve you get is an ellipse, and the center of the cone is one focus of the ellipse.
Aug
29
comment What is the possibility of a railgun assisted orbital launch?
@Phill: That exponential formula only applies for rockets that have to hoist the fuel they will use further up.
Aug
29
comment What is the possibility of a railgun assisted orbital launch?
I have to wonder, what is the effect of air friction? It's being shot in the thickest air at what, Mach 25? Seems you need to add a nose cone and some extra speed, just to have enough speed left when you get out of lower atmosphere.
Aug
27
comment How much thrust would be needed to turn a hobbyist weather balloon into a deep space probe?
+ Yeah. It's a classic mistake. Getting into space takes a small fraction of the energy of getting into orbit, let alone escaping.
Aug
20
comment How fast would someone have to run to run over water?
Well, if you could run this fast...
Aug
18
comment How to compute the speed necessary for an airplane to fly?
@Rody: OK, you win :) I'm just a pilot.
Aug
18
comment How to compute the speed necessary for an airplane to fly?
@Rody: The relationship between the Bernoulli effect and downwash is very simple: you can't have one without the other. Regarding inverted flight, it's simply a matter of the angle of attack (which directs the downwash), and that affects the point at which the air approaches the rounded leading edge, which affects the difference in distance traveled by the air over one side of the wing versus the other. This has been thoroughly discussed.
Aug
17
comment How does a car turn without any skidding?
@RodyOldenhuis: Then it can turn in a circle about the center of the rear wheel. Then what I said earlier about there being some skidding at the rear wheel due to the width of the contact patch applies.
Aug
17
comment How does a car turn without any skidding?
@mcFreid: I think you're having trouble visualizing the contact patch as being just a point. For a real rubber tire, it is not a point, so there is something funny going on, but it is accomodated by the flexibility of the rubber.
Aug
17
comment How does a car turn without any skidding?
@mcFreid: In order to skid, there has to be a contact point with a sideways component of velocity. Where is it?
Aug
17
comment How does a car turn without any skidding?
@mcFreid: Actually, since a tire contacts the road in a patch, not a point, the side of the patch away from C does have to travel a larger distance. So it does skid a little bit that depends on how wide the tire is.
Aug
17
comment How does a car turn without any skidding?
@mcFreid: As long as we're simplifying, idealize the wheel to be zero width (a knife edge of super-hard material). It rolls forward and backward without slipping. The path on which it rolls does not have to be perfectly straight, does it? From instant to instant, it can turn a little bit without slipping, because it contacts the road at an infinitessimal point.
Aug
16
comment What would be an appropiate shape for a parachute?
@user1002327: It's the same as in any aircraft. For the given weight and wing area, there is a speed that's too slow, called the "stall speed", where the wing ceases flying and becomes a parachute. The speed that gives maximum time aloft is just above stall speed. You adjust the speed by trimming the weight more or less forward.
Aug
12
comment What differs string theory from philosophy or religion?
@Ron: I should clarify that the comment regarded a time before Christianity really got going, and the religions being talked about were whatever the various tribal peoples being conquered happened to have.
Aug
12
comment What differs string theory from philosophy or religion?
If can interject a slightly humorous aside, Gibbon, in "Decline and Fall of the Roman Empire" related that adherents of religions knew they were true, philosophers knew they were false, and magistrates knew they were useful.
Aug
12
comment What is the relationship between kinetic energy and momentum?
Look here.
Aug
8
comment Why are radians more natural than any other angle unit?
I seem to remember when it was considered to divide the circle into 400 "degrees", to make navigation a little less error-prone. As it is, pilots have to just "know" that 7 and 25 are opposite ends of a runway, and be really really careful not to mix up 13 and 31.
Aug
8
comment Why are radians more natural than any other angle unit?
Nice...........
Jul
26
comment Rotation, cats landing on their feet, and conservation of angular momentum
@Physikslover: No need to reason about it, try it. Sit on a bar stool. Hold a heavy weight in one hand, hanging at your side. Then swing it up to horizontally in front of you (call that 12 oclock). Then swing it horizontally to the 3:00 position. That will of course turn you somewhat to the left. Then drop the weight back down to your side, where it started from. Now you are just as you were when you started, except you remain oriented to the left of where you started.
Jul
26
comment Rotation, cats landing on their feet, and conservation of angular momentum
@Physikslover: Relative rotation does not require a swivel joint. Have you ever tried to swing a hula-hoop around your waist? It's the same motion. If you do that while standing on a frictionless platform, you will turn, and when you stop, you will be facing in a new direction. Alternatively, sit on the bar stool and swing your feet in a circle.