Hi David, Richard et. al. None of us is picky, we are discussing things.
1. David, you wrote >Flight would work quite well without viscosity. The lift generated by >aircraft wings is due to a pressure difference above and below the wing, >and this is created by the shape of the wing. Whilst viscosity is a >consideration in the real world, lift effects can certainly be modelled in >a non-viscous fluid. (I did a course in Fluid Dynamics with the Open >University a couple of years ago.) > >A more interesting version occurs when a rotating cylinder is placed >perpendicularly in a fluid flow. This generates lift too, at right angles >to the direction of flow and the axis of the cylinder. This theory was >used some time ago on German rotor ships, and I suspect is also the theory >behind a "new" aeroplane shown on Tomorrow's World last week. The pressure difference is al right but how could you apply it to the wing if everything smoothly slides? It is even easier to explain with the rotating cylinder. If there is no viscosity it does not matter whether the cylinder rotates or not. It is not able to accelerate air particles on one side and deccelrate on the other because it is not able to catch them. The flow remains ideally symmetric so the lift force cannot appear. So no viscosity, no lift. BTW, flow around rotating cylinder may be transformed mathematically to flow around any other shape. 2. It is hard to say what is going to happen to GMT. Certainly international community is no longer using even the name. I do, because I am a bit traditionalist, like I think most of the list members. 3. Richard you mentioned that UT1 does not take into account polar movements, This is the citation from your paper on http://www.rnw.nl/realradio/information/html/universaltime.html " There are actually a couple of variants of UT. UT as determined by actual astronomical observations at a particular observatory is known as UT0 ("UT-zero"). It is affected by the motion of the earth's rotation pole with respect to the crust of the earth. If UT0 is corrected for this effect, we get UT1 which is a measure of the true angular orientation of the earth in space. " Whatever the interpretation (my secondary language is C++, not English) the paper is very good and you deserve any kind of malt you like (for now be happy with virtual one). Slawek At 07:37 AM 3/1/99 -0500, David Higgon wrote: >Slawomir and all, > >I don't want to be too picky, but since you are interested in side >threads... > >Flight would work quite well without viscosity. The lift generated by >aircraft wings is due to a pressure difference above and below the wing, >and this is created by the shape of the wing. Whilst viscosity is a >consideration in the real world, lift effects can certainly be modelled in >a non-viscous fluid. (I did a course in Fluid Dynamics with the Open >University a couple of years ago.) > >A more interesting version occurs when a rotating cylinder is placed >perpendicularly in a fluid flow. This generates lift too, at right angles >to the direction of flow and the axis of the cylinder. This theory was >used some time ago on German rotor ships, and I suspect is also the theory >behind a "new" aeroplane shown on Tomorrow's World last week. > > >Going back to GMT, UTC and Internet Time, maybe the latter will come into >use, albeit in the far future... >If the Earth is slowing in its rotation, there will come a time when a day >last 25 of our present hours. GMT (I think, in its old sense) would still >divide the day into 24 hours, and this is obviously well past the point >where the introduction of some leap seconds is going to bring UTC back in >line with GMT! People would be unwilling to use UTC as this would mean >breakfast would be an hour later each day, and scheduling appointments in >the future would require a knowledge of the date to determine where the >time was. Similarly the scientific community could not use GMT as its >"seconds" would be 4% too long. The solution would seem to be UTC for the >scientists who need to measure seconds, and some sort of civil time for >general use. To avoid confusion, the name "seconds" should probably not be >used - why not "beats" - and while we're at it, why not embrace >decimalisation and have ... Internet Time! > >I for one won't be touching Internet Time with a barge pole, and thankfully >I'll be long gone before there's enough of a difference between GMT and UTC >to warrant its introduction ;-) > >David Higgon >Young stick in the mud! > Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
