8,422 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 8 months
seen 1 hour 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.


Jan
26
comment Am i trying to fly by pulling myself up by my hair?
You might try a lever arrangement, so the downwash is not hitting the scale.
Jan
26
comment Can a car steer on a frictionless surface?
@EmilioPisanty: I don't think the front wheels on a car (on the frictionless surface) can change the car's pointing direction, because those wheels are not free to precess at right angles to the direction in which they are turned, because the car cannot bank (as a motorcycle can). You would need to have a gyroscope mounted in the vehicle, and it would need to be free to take on a bank angle. The amount it would need to bank would depend on its angular momentum.
Jan
20
comment Alternative air transportation and magneto-aerodynamics
There have been "flying saucer" aeronautical projects, of varying degrees of success.
Jan
20
comment Helicopter, Tricopter, Quadccopter - what's really happening here? Are there generalized advantages on a small scale?
For efficiency, the longer and thinner the blades, the better. Smaller rotors are less efficient, thus less flying duration. If you have an odd number of lifting rotors, you have net torque, so you need a tail rotor. Planes with lifting rotors can hover, but planes with wings have to fly in circles if they want to stay in one place. Put all those considerations together.
Jan
14
comment Problem regarding Archimedes Principle
It's a spring-mass-dashpot system (ignoring the dashpot). You can figure out the amount of mass, and you can figure out the spring constant (dForce/dY). Then look up the equation.
Jan
9
comment Turning an Airplane. What actually causes the circular motion in a banked (roll) turn?
@David: Your instinct is right. The tail acts as a weather-vane, which is the same as saying if the fuselage gets sideways to the relative wind, the tail (vertical stabilizer) feels that wind, creating a torque to turn the craft's nose into the wind. (Losing that tail is a good way to crash, because then nothing can stop the plane from going sideways.)
Jan
6
comment Different sized pneumatic Pistons
@TwoShorts_: I don't know what else to say. At the same pressure, force is proportional to area.
Jan
6
comment Turning an Airplane. What actually causes the circular motion in a banked (roll) turn?
@David: Neither. When you ride a bicycle in a circle, what causes the turn? It is the fact that you are leaning. That creates a sideways force. If there is a sideways force, there is no way you can go in a straight line - you have to turn. Banking an airplane and leaning a bicycle are the same thing. All the tail does is keep you pointing in the direction of travel.
Jan
6
comment Different sized pneumatic Pistons
Well then you can answer it yourself. Just suppose one piston has a surface area of 1 square centimeter, and the other is the size of a football field, and the air pressure on each one is the same per square centimeter. Suppose each one is actually a suction cup. Which would be harder to lift?
Jan
6
comment Different sized pneumatic Pistons
You mean with different area? Force is pressure times area.
Dec
30
comment Is there a way to convert CFM (rate of air moved) to kilograms of lift generated?
Force is momentum per unit time, so it's not just the mass of air moved, it is mass times the change in velocity.
Dec
16
comment If an airplane is flying sideways, is it in free fall?
@Vivek: There's a maneuver called a knife edge where the wings are at 90 degrees to the ground. What the rudder does is put the fuselage sideways to the wind, generating the lift that holds the aircraft against gravity. Generally any such use of the rudder is called a slip or skid.
Dec
16
comment If an airplane is flying sideways, is it in free fall?
@Vivek: Yes, but would you call it free-fall? The pilot could be pulling 4G or more in that horizontal direction.
Dec
15
comment Can the weight of a bird be measured, considering air friction?
@Santhi: It comes out as extra air pressure on the bottom of the box. The wings get lift by pushing air downward, which hits the bottom of the box, which pushes the air back up so it stays in the box. That means the bottom of the box is feeling more pressure.
Dec
11
comment Does juggling faster less work then juggling slower?
Before you hoist a ball to a height, it falls into your hand from the same height, so in principle it takes zero work for any height. So it all depends on how efficient your muscles and joints are.
Dec
10
comment Where can I get fluidics components?
Excellent question, though some may think it is off-topic for physics. If I were you, I would start thinking about 3-d printers.
Dec
8
comment How to approximate lag of roll of a bird (or RC airplane)?
@Yeti: You're probably only able to estimate an approximate value. There's guesswork no matter how you do it.
Dec
3
comment Gravitational field intensity inside a hollow sphere
I like Qmechanic's answer, but my own intuition is this: suppose the shell consists of a lot of small "moons" covering the shell. You could be close to one and feeling its gravity, and the ones "across" the way have gravity that falls off at $d^2$, but the number of them increases with $d^2$, so they are just as powerful as the one you are next to.
Dec
3
comment Calculating the force required to lift a weight with a screw
He's ignoring friction, so it's just an energy balance. The energy put into lifting the weight is what? 2000 lb * 1 inch = 2000 inch-lbs. That handle must be pushed 1260 inches to get the same energy, and 1260 inches * 1.6 lb ~ 2000 inch-lbs. What's this dimensional analysis you're talking about?
Dec
2
comment Why is a thought experiment a valid way to prove anything?
@Albalma: Next to Feynman's lectures, this is my favorite book on relativity. The author was teaching relativity in a continuing-ed class where people were math-phobic, so he does a great job of making it accessible.