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Pastimes : The New Qualcomm - write what you like thread. -- Ignore unavailable to you. Want to Upgrade?

To: Maurice Winn who wrote (3093)	7/12/2001 10:36:14 AM
From: Uncle Frank	Read Replies (1) \| Respond to of 12231

Another cherished belief shattered. Which Way Will my Bathtub Drain? Question: Does my bathtub drain differently depending on whether I live in the northern or southern hemisphere? Answer: No. There is a real effect, but it is far too small to be relevant when you pull the plug in your bathtub. Because the earth rotates, a fluid that flows along the earth's surface feels a "Coriolis" acceleration perpendicular to its velocity. In the northern hemisphere, Coriolis acceleration makes low pressure storm systems spin counterclockwise; however, in the southern hemisphere, they spin clockwise because the direction of the Coriolis acceleration is reversed. This large-scale meteorological effect leads to the speculation that the small-scale bathtub vortex that you see when you pull the plug from the drain spins one way in the northern hemisphere and the other way in the southern hemisphere. But this effect is VERY weak for bathtub-scale fluid motions. The order of magnitude of the Coriolis acceleration can be estimated from size of the "Rossby number" (1) (see below). The effect of the Coriolis acceleration on your bathtub vortex is SMALL. To detect its effect on your bathtub, you would have to get out and wait until the motion in the water is far less than one rotation per day. This would require removing thermal currents, vibration, and any other sources of noise. Under such conditions, never occurring in the typical home, you WOULD see an effect. To see what trouble it takes to actually see the effect, see the reference below. Experiments have been done in both the northern and southern hemispheres to verify that under carefully controlled conditions, bathtubs drain in opposite directions due to the Coriolis acceleration from the Earth's rotation (2). Coriolis accelerations are significant when the Rossby number is SMALL. So, suppose we assume a Rossby number of 0.1 and a bathtub-vortex length scale of 0.1 meter. The Rossby number is defined as Rossby number = U/(2Lw) where U is the velocity of a fluid element, L is the scale of the fluid motion, and w is the earth's rotational velocity ( = 1 rotation/day). In conventional units, the earth's rotation rate is about 10^(-4)/second, so solving the above equation for the fluid velocity, we get that Coriolis acceleration in your bathtub is significant for fluid velocities of less than 210^(-6) meters/second. This is a very small fluid velocity. How small is it? Well, we can take the analysis a step further and calculate another, more famous dimensionless parameter, the Reynolds number. The Reynolds number is = LUdensity/viscosity Assuming that physicists bathe in hot water the viscosity will be about 0.005 poise and the density will be about 1.0, so the Reynolds Number is about 410^(-2). Now, life at low Reynolds numbers is different from life at high Reynolds numbers. In particular, at low Reynolds numbers, fluid physics is dominated by friction and diffusion, rather than by inertia: the time it would take for a particle of fluid to move a significant distance due to an acceleration is greater than the time it takes for the particle to break up due to diffusion. The same effect has been accused of responsibility for the direction water circulates when you flush a toilet. This is surely nonsense. In this case, the water rotates in the direction which the pipe points which carries the water from the tank to the bowl. References: (1) J. Pedlosky, "Geophysical Fluid Dynamics" sec 1.2 (2) Trefethen, L.M. et al, Nature 207 1084-5 (1965).

To: Maurice Winn who wrote (3093)	7/12/2001 10:39:29 PM
From: Drew Williams	Read Replies (2) \| Respond to of 12231

Back in the dark ages (1993-95) when I was forced to use a Macintosh at the office, I also used the then current version of Netscape's web browser, aka Navigator. I don't know whether Microsoft even made a version of Internet Explorer for the Mac at that time. Anyway, on my Windows 3.11 PC at home, I installed Netscape so what I saw there would be as similar as possible as at the office. Somwhere along the line I built a new PC and installed Windows 95, which had Internet Explorer, which I have used ever since, upgrading whenever Microsoft suggested it. I now use version 5.5 on Windows 98 SE. In my humble opinion as someone who has spent a lot of time working with PC's for twenty years (I managed a Radio Shack Computer Center for six years in the eighties) and until recently tried out all sorts of software on a regular basis, I never was able to see any reason why I should choose Netscape Navigator over Microsoft's Internet Explorer or the other way around. For me, they were functional equivalents with no significant value proposition either way. I understand the discussion about Microsoft's alleged monopolistic practices and how they harmed Netscape, but I have a lot of trouble getting too excited about it. I think the natural place for a browser is as part of the operating system. I think the same way about the RealPlayerPlus and RealJukebox icons on my taskbar. Perhaps I would feel differently had I invested in Netscape or Real Networks. For the record, I have never directly invested in any of the companies I mentioned above, although the mutual funds in my IRA and 401k have certainly owned Microsoft. In fact, right now the only equity I own is Qualcomm. (So I'm smiling today!)