BikerBabe 0 #26 December 10, 2003 Sorry...it does. at least to me. I forgot you had posted it when I posted! Never meddle in the affairs of dragons, for you are crunchy and taste good with ketchup! Quote Share this post Link to post Share on other sites
kallend 2,146 #27 December 11, 2003 QuoteQuotebut Newton says that every action has an equal and opposite reaction. SO what do you call the equal but opposite force to the centripetal force?The centripetal force to keep you spinning is provided by the lift of your improperly oriented canopy. The equal and opposite force is on the air molecules passing over the lower surface of the wing. (Bernoulli's Principle) I did not make myself clear enough. The lines are in tension and exert a force on the skydiver to provide a centripetal acceleration. What do you call the inertial reaction to that? You could put a force balance in the lines and measure that force so it can hardly be fictitious.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
pilotdave 0 #28 December 11, 2003 ficticious is just the wrong word. pseudo is more like it. said it yourself. (yes, i realize you understand this better than any of us anyway Dave Quote Share this post Link to post Share on other sites
kallend 2,146 #29 December 11, 2003 Quoteficticious is just the wrong word. pseudo is more like it. said it yourself. (yes, i realize you understand this better than any of us anyway Dave It has always irritated (just a little) that despite the fact that all known intelligent life in the universe lives in a rotating reference frame, some physicists insist on dismissing forces easily measurable in that frame as non-existent. I might add that my old (very old now) physics prof, Sir Brian Pippard FRS, who was nominated for but never won a Nobel (although one of his students, Brian Josephson, did), was quite content to talk about centrifugal force and Coriolis force. He said there were certain words that we discourage children from using, but they were OK for adults, and these included "centifugal" and "coriolis".... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
brewman 0 #30 December 11, 2003 centrifugal force is not a "true force", but an "inertial force" (some people say "false") that manifests itself inside an accelerated frame of reference. See http://www-istp.gsfc.nasa.gov/stargaze/Sframes2.htm for a good explanation. Quote Share this post Link to post Share on other sites
kallend 2,146 #31 December 11, 2003 Quote But the point is, when you cut away from a spinning mal, you don't go flying outwards do to the centrifugal force. You fly off tangential to the circle due to the lack of centripetal force. Dave That depends on your point of view. If an observer is on the axis of rotation and rotating with the system, then the object cut way does indeed fly outwards (and backwards, Coriolis effect) from the point of view of that observer. It's all a matter of how you make the observation. A good physicist or engineer will handle a problem in the most convenient way, which might well be in the rotating frame. Example: the problem of predicting the impact point of long range artillery. Very inconvenient to convert to a non rotating frame, do the calculation with "real" forces (air resistance is a nightmare this way since the atmosphere is still rotating but your new reference frame isn't), and convert back to the Earth. Much easier to do it all referenced to the Earth and throw in the Coriolis "force" which is easily computed.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
champu 1 #32 December 11, 2003 QuoteIt has always irritated (just a little) that despite the fact that all known intelligent life in the universe lives in a rotating reference frame, some physicists insist on dismissing forces easily measurable in that frame as non-existent.If you want to carry the problem into a rotating reference frame, that's fine. In such a frame you will get a pretty simple static setup with two objects pulling in opposite directions on each other. However in this situation, I don't feel we gain anything by setting it up like this. The description of what is happening to the jumper/parachute before the spin is started, and after a cutaway takes place becomes hopelessly mired when trying to use a rotating frame of reference. I could create a frame of reference that was travelling east at 1+cos(10t) and there'd be all kinds of forces acting on the spinning jumper, it doesn't mean it's necessarily useful to discuss them. From a stationary point of reference, the description of the system before, during, and after the spin is incredibly simple. Quote Share this post Link to post Share on other sites
kallend 2,146 #33 December 11, 2003 QuoteQuoteIt has always irritated (just a little) that despite the fact that all known intelligent life in the universe lives in a rotating reference frame, some physicists insist on dismissing forces easily measurable in that frame as non-existent.If you want to carry the problem into a rotating reference frame, that's fine. In such a frame you will get a pretty simple static setup with two objects pulling in opposite directions on each other. However in this situation, I don't feel we gain anything by setting it up like this. The description of what is happening to the jumper/parachute before the spin is started, and after a cutaway takes place becomes hopelessly mired when trying to use a rotating frame of reference. I could create a frame of reference that was travelling east at 1+cos(10t) and there'd be all kinds of forces acting on the spinning jumper, it doesn't mean it's necessarily useful to discuss them. From a stationary point of reference, the description of the system before, during, and after the spin is incredibly simple. Define stationary. Transformations between frames are pretty easy matrix operations. I contend that if you were living in a space station generating artificial "gravity" by spinning like in "2001 A Space Odyssey", that use of that rotating frame to describe the behavior of objects inside the station to the astronauts living there would be just as easy, and probably much easier, than the use of a non-rotating frame.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
Designer 0 #34 December 11, 2003 Glad somebody finally got it right! Quote Share this post Link to post Share on other sites
pilotdave 0 #35 December 11, 2003 Yeah but when the space shuttle disconnects from the spinning space station, which NASA exec screwed up? This is sounding like the aircraft flight dynamics course I took last year. Describing the motions of an aircraft in all different reference frames and converting it back and forth. Pseudo-inertial axes, aircraft axes, wind frame axes. I really shoulda taken some linear algebra... Dave Quote Share this post Link to post Share on other sites
kallend 2,146 #36 December 12, 2003 QuoteYeah but when the space shuttle disconnects from the spinning space station, which NASA exec screwed up? This is sounding like the aircraft flight dynamics course I took last year. Describing the motions of an aircraft in all different reference frames and converting it back and forth. Pseudo-inertial axes, aircraft axes, wind frame axes. I really shoulda taken some linear algebra... Dave I hate to bring up a dreadful movie, but in Armageddon, did anyone notice that the "gravity" vector in the shuttle was 90 degrees off from the direction it should have been when the shuttle was docked on the space station? Not that that was the only physics error in Armageddon.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
rehmwa 2 #37 December 12, 2003 Unless the interior was all built sideways. ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
kallend 2,146 #38 December 12, 2003 Quote Unless the interior was all built sideways. Maybe it was like a Tardis where the inside and outside are totally unrelated.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
NoShitThereIWas 0 #39 December 12, 2003 Ok so I have a question ... those rides you go on at an amusement park, where you stand up and your back is leaning against the pad. It spins and you feel the force in your tummy and everywhere else ... the centripetal force is accelerating you toward the middle or the axis and the centrifugal or pseudo force is what you feel in the opposite direction??? How can an equal and opposite force be a pseudo force?Roy Bacon: "Elvises, light your fires." Sting: "Be yourself no matter what they say." Quote Share this post Link to post Share on other sites
kallend 2,146 #40 December 12, 2003 QuoteOk so I have a question ... those rides you go on at an amusement park, where you stand up and your back is leaning against the pad. It spins and you feel the force in your tummy and everywhere else ... the centripetal force is accelerating you toward the middle or the axis and the centrifugal or pseudo force is what you feel in the opposite direction??? How can an equal and opposite force be a pseudo force? If you look at it in a non-rotating reference frame (a spectator watching the ride) the centripetal force is an unbalanced force applied by the frame of the rider that results in their acceleration. For the engineer making the ride, the steel frame is rotating, and in that frame the steel definitely has to support an outward directed force from the riders. The stress in the frame is measureable and quite real. It's all a matter of convenience. If I had to find the equation of motion of a pendulum bob swinging in the artificial gravity of a spinning space station, I would choose to do it in the rotating reference frame because that way is far easier than transforming the entire problem to a fixed frame and solving that. As my old physics prof said about "centrifugal" and "Coriolis", adults can use words that children shouldn't.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
