Ballistic Theory, Progress report...Suitable for 5yo Kids
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From: Eric Gisse on 11 Nov 2005 17:56 Paul B. Andersen wrote: [snip] > I think E = mc^2 follows from Maxwell's equations, > EM-radiation has momentum. That seemed highly reasonable to me. Though I was hoping for Henri to do it instead of you. > > Paul
From: bz on 11 Nov 2005 20:09 HW@..(Henri Wilson) wrote in news:tt6an15l08vsrcr572n5rahv3oeels5742(a)4ax.com: > Paul I understand perfectly what you are saying. > I still find it hard to believe, particularly when the plane is > decelerating. > >>A modern fighter is like that. It can't go straight ahead >>without continuous corrections. > > The article claims certain advantages in this...presumably less > drag...OK... They are designed that way in order to increase their manoverability, not to decrease drag. >>A man is fast enough to back with a trailer - if he >>drives slowly. But try to back at 100 km/h (60 mph)! >>It can't be done. But a computer could. > > Yes Paul. I understand that. > I still find it hard to believe that the plane is unstable in all > situations. Perhaps it only becomes unstable above a certain speed. That > I can accept. > Facts do not depend upon your acceptance. The aircraft in question are inherently unstable at ALL speeds where they have enough lift to fly. -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: Eric Gisse on 11 Nov 2005 20:36 Henri Wilson wrote: > On Fri, 11 Nov 2005 14:36:18 +0100, "Paul B. Andersen" > <paul.b.andersen(a)hiadeletethis.no> wrote: > > >Eric Gisse wrote: > >> Henri Wilson wrote: > >> > >>>On 8 Nov 2005 19:19:07 -0800, "Eric Gisse" <jowr.pi(a)gmail.com> wrote: > >>> > >>> > >>>>Jerry wrote: > >>>> > >>>>>Henri Wilson wrote: > >>>>> > >>>>>>On 8 Nov 2005 14:13:58 -0800, "Eric Gisse" <jowr.pi(a)gmail.com> wrote: > >>>>> > >>>>>>>So, E=mc^2 was not known before 1905. You cannot prove otherwise. > >>>>>> > >>>>>>It was obvious. > >>>>>>Just integrate mv.dv from 0 to c. > > > >What a stupid proposition. > >This integral gives the kinetic energy of a mass > >m going at the speed c, according to Newton. > > > >This has obviously nothing whatsoever to do > >with the energy content of a mass m at rest. > > It might have. ....correct form. Incorrect form because it is the wrong answer. You are repeating the same idiocy Schoenfeld displayed here: http://groups.google.com/group/alt.sci.physics/msg/96fc6ffc533b82ea Just because it is similar does not mean it is the same. At least he had the benefit of having obtained the correct answer. [snip]
From: Black Knight on 11 Nov 2005 23:48 "Henri Wilson" <HW@..> wrote in message news:dq6an1t2ua653vhr2unrjjr1e3dvgj5krj(a)4ax.com... > On Fri, 11 Nov 2005 14:36:18 +0100, "Paul B. Andersen" > <paul.b.andersen(a)hiadeletethis.no> wrote: > >>Eric Gisse wrote: >>> Henri Wilson wrote: >>> >>>>On 8 Nov 2005 19:19:07 -0800, "Eric Gisse" <jowr.pi(a)gmail.com> wrote: >>>> >>>> >>>>>Jerry wrote: >>>>> >>>>>>Henri Wilson wrote: >>>>>> >>>>>>>On 8 Nov 2005 14:13:58 -0800, "Eric Gisse" <jowr.pi(a)gmail.com> wrote: >>>>>> >>>>>>>>So, E=mc^2 was not known before 1905. You cannot prove otherwise. >>>>>>> >>>>>>>It was obvious. >>>>>>>Just integrate mv.dv from 0 to c. >> >>What a stupid proposition. >>This integral gives the kinetic energy of a mass >>m going at the speed c, according to Newton. >> >>This has obviously nothing whatsoever to do >>with the energy content of a mass m at rest. > > It might have. ....correct form. > >> >>>>>>Are you out to prove that well over two centuries in development >>>>>>of mathematics must be thrown out the window, the same as >>>>>>virtually all of physics? Shall we call your new system of >>>>>>mathematics wcalculus? >>>>> >>>>>int(mv,dv) = mv^2/2 >>>>> >>>>>Henri has shown many times he consideres being off by a factor of 1/2 >>>>>"close enough" to the real answer. >>>>> >>>>>I'm kinda getting tired of dealing with his idiocy, actually. >>>>>Mathematical subtilties like "being correct" are completely lost upon >>>>>him. >>>> >>>>can't you see where the other 1/2 comes from? >>> >>> >>> It is not my problem if you can't even work an integral. It is not my >>> job to invent explanations for *your* failures. >> >>The 1/2 is a bit beside the point anyway. >>The important point is that the E in E = mc^2 is not kinetic energy. >> >>Henry Wilson has no clue how to derive this equation. >> >>However, it may have been done before 1905, because >>it is possible to derive it using only Newtonian mechanics >>and Maxwell's equations. >> >>The following thought experiment was devised by Einstein, >>and is commonly referred to as "Einstein's box". >> >>I will describe it in my own words. >> >>Given a box with mass M and length L. >> From one side of the box, an EM radiation pulse >>with energy E is emitted. According to Maxwell, >>the momentum of the pulse is p = E/c. >>The time for the pulse to traverse the box is t = L/c. >>Conservation of momentum say that the box will move >>with the speed given by Mv = E/c, v = E/Mc while the pulse >>is on its way. When the pulse hits the other wall, the box >>is stopped. >>So the box has moved a distance d = vt = (E/c^2)L/M. >>But the mass-centre of the box must remain stationary. >>That means that a mass m must have moved along with the pulse >>so that m*L = M*d = (E/c^2)L >>Thus m = E/c^2 >> >>I think E = mc^2 follows from Maxwell's equations, >>EM-radiation has momentum. >> >>Paul > > Geese will still want to argue. > > > HW. Message rating several casks. Androcles.
From: Black Knight on 11 Nov 2005 23:48
"Henri Wilson" <HW@..> wrote in message news:tt6an15l08vsrcr572n5rahv3oeels5742(a)4ax.com... > On Fri, 11 Nov 2005 10:49:02 +0100, "Paul B. Andersen" > <paul.b.andersen(a)deletethishia.no> wrote: > >>Henri Wilson wrote: >>> On Wed, 09 Nov 2005 23:50:03 +0100, "Paul B. Andersen" >>> <paul.b.andersen(a)deletethishia.no> wrote: > >>> >>>>It is a long time since fighters were stable. >>>>They cannot be flown without a computer. >>>>Not even close. >>>>With traditional control, a man would simply not be fast enough >>>>to keep control of the plane. >>> >>> >>> Yes that is pretty obvious. >> >>Is it? >>I am not convinced you have grasped the point. > > I do. > One might compare this with the way a rocket is kept vertical during > lift-off. > >>A traditional aircraft - say like a small Cessna - is stable. >>That means that if the pilot leaves the aircraft to itself, >>it will keep going straight ahead (provided that trim tabs etc. >>are set properly). That means that if the plane by some reason >>veers a little around one of its axes, it will automatically >>correct itself. A non R/C model aircraft flies itself. >>It can do that because it is inherently stable. Real aircrafts >>are traditionally built after the same principles. >>But modern fighters are inherently unstable. That means that >>if it veers a little around one of its axes, forces will be >>induced which make it veer more in the same direction, >>unless it is corrected - fast! >> >>It could be compared to driving with a trailer. >>While driving forward the trailer will automatically >>follow the car. It is a stable system. But backing is another >>story. If the trailer has a small angle to the car, >>this angle will increase unless the driver corrects it. >>It is impossible to back along a given curve without >>continuous corrections on the steering wheel. It is >>an unstable system. > > Paul I understand perfectly what you are saying. > I still find it hard to believe, particularly when the plane is > decelerating. > >>A modern fighter is like that. It can't go straight ahead >>without continuous corrections. > > The article claims certain advantages in this...presumably less > drag...OK... > >>A man is fast enough to back with a trailer - if he >>drives slowly. But try to back at 100 km/h (60 mph)! >>It can't be done. But a computer could. > > Yes Paul. I understand that. > I still find it hard to believe that the plane is unstable in all > situations. > Perhaps it only becomes unstable above a certain speed. That I can accept. > >>>>And it probably isn't possible even if he were. >>>>The control panels don't move as you would expect them to. >>>>For example, the right and left elevator may move in opposite >>>>direction. And the ailerons may move in the same direction. >>>>And then there are those two extra control panels underneath >>>>the plane. >>>> >>>> >>>>>I think such a servo control system would only apply during fast >>>>>maveuvering. >>>> >>>>It's much more than a servo control. >>>>The pilot tells the plane what he want it to do, and the computer >>>>figure out how to do it. For example, if you pull the stick hard, >>>>it means up as fast as possible. The plane will then pull up as >>>>fast as it can without structural damage. (The pilot may pass out, >>>>but the plane will stay in one piece.) >>> >>> >>> The pilot still has to think fast enough to make the plane do what he >>> wants. >> >>Obviously. :-) >> >>> The electronics just carries out his instructions. >> >>No, it does much more than that. Even with no input from >>the pilot, it must continuously correct for the plane's >>tendency to veer off course. It is so bad that if it didn't, >>the plane would after a short time go into spin. > > Yes, just as a vertical rocket will veer off course and crash if the > nozzles > aren't adjusted quickly enough. > . > >>>>>...but any remote electronic system must work on the principle of >>>>>sensing and >>>>>reducing an error. One of the big problems is to find a decent >>>>>compromise >>>>>between reaction time, senstivity and damping. One must prevent the >>>>>thing from >>>>>building up an oscillation. >>>> >>>>It's very different from traditional servo loops. >>> >>> >>> Well its a bit like electronic power steering of a car(which hasn't been >>> introduced yet) but the basic problems remain. >> >>"A bit like" maybe, but just a very small bit. :-) >>It is a multi variable control system. >>That means that a number of inputs (rotations around >>and accelerations along the different axes) affects >>a number of outputs (the angle of the different control >>panels). It can not be divided into a number of >>one input - one output control loops. >>It's a beast of a control system. >> >>Which (- to a Norwegian's malicious pleasure -) was >>demonstrated by the Swedish JAS fighter. It crashed >>twice because the control system didn't work properly. >> >>http://www.nearlygood.com/video/crashlanding.html >>The pilot survived - and crashed a second time >>at an air show! He ejected, and survived again. >>He is probably getting used to it! :-) > > As I said, I hope I never have to fly in one. > >> >>Paul > > > HW. Message rating several casks. Androcles. |