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My academic interests are in power plants of all types, shapes, and sizes, and how well they play with each other. My hobbyist interest are kind of all over the place. I like the maker movement, I'm most interested in the sensors and data, the "internet of things" kind of stuff. In physics, I'm probably the most curious about general relativity topics, but I'm all over the place. We once had a Nuclear Engineering proposal on Area 51, but it failed.


1d
comment Calculating the drag force provided by a laminar flow
Restrictions for high numbers? Not likely. Consider atmospheric reentry - projectiles will vaporize before the drag equation loses its validity. This is because the equation is valid for totally ballistic particle collisions. The drag coefficient will change, but that's always dependent on the specific flow pattern anyway. Even when the mean free path is larger than the projectile, it works. Just assume there is just a column of particles in front that bounce off in some constant angle, you get the v^2 form. That's different from the normal application, but it's also strangely the same...
1d
comment Calculating the drag force provided by a laminar flow
The drag model does have such restrictions. It will actually under-estimate the drag for low Reynolds numbers, particularly if it is much less than 1. If you're calculating some transit time for some very small thing, the drag model will give answers which are way off.
Jul
21
comment Could a vacuum airship be possible?
There's no law that says it must be a large monolithic sphere like a hot air balloon. Larger sizes have increasing problems in compression due to buckling. You would, instead, use a large number of tiny vacuum spheres. This would get you the closest to the theoretical limits you've referenced here. At those sizes, you might be able to use electrical charge to balance the crushing pressure, and then you'd surpass the theoretical limits. How to build it is a different story.
Jul
13
revised Size of black hole so large that I could pass event horizon without dying from tidal forces?
typo
Jul
13
answered Size of black hole so large that I could pass event horizon without dying from tidal forces?
Jul
11
answered Calculate pressure with the ideal gas law or $\rho gh$?
Jul
11
revised Grounding a capacitor
grammar
Jul
9
answered Grounding a capacitor
Jun
27
answered Why do two ends of a long conducting wire have the same electric potential?
Jun
13
comment Can lift contradict conservation of energy?
@Chris Yes, that is what I was claiming in very clear terms. Obviously I haven't ran the math, but I suspect that this effect alone can rule out the perpetual motion possibility.
Jun
12
awarded  Nice Answer
Jun
12
answered Can lift contradict conservation of energy?
Jun
1
awarded  Popular Question
May
26
comment How to find set point for PID controller for self balancing robot?
Perhaps hold it upside-down by the wheels and make note of the reading at this point. Then use some math to rotate 180 degrees. It sounds childishly simple but it might work for your issue.
May
25
answered Is Torricelli's law “wrong” for big holes? - Tank draining problem
May
5
comment Hydrogen-boron fusion
The electron cloud does have a role, just as you described, related to penetration depth. However, I would also like to add that the nucleus' own electrostatic repulsion has a large role in poor "efficiency". The straightforward ratio of scattering to fusion events aren't enough to make a profit of energy from the first collision. This is why the DPF attempts to create a hot plasma ball that enables many successive collisions. In accelerator-target designs, you can only hit 1 or 2 nuclei before you've lost most kinetic energy.
Apr
29
awarded  Notable Question
Apr
27
comment Is the planet Mesklin as described in Hal Clement's Mission of Gravity correct?
@EmilioPisanty You are, of course, strictly correct. But for that matter, when you start walking, you'll kick in dynamic components like the Coriolis force. Thus, we can't conclusively accept your narrative from a map of the field by itself (or without other assumptions, like walking "slowly"). For Mesklin itself, it would be like a cross-continent train ride raises your head less than 60 feet. For Saturn, it would be like 2 inches.
Apr
27
revised Is the planet Mesklin as described in Hal Clement's Mission of Gravity correct?
added 361 characters in body
Apr
24
comment Is the planet Mesklin as described in Hal Clement's Mission of Gravity correct?
@TimB Ugh, I just realized one of those nasty more complicated details. The field I drew is not conservative, which means you could make energy from it. It also means that the blue line isn't truly equipotential. However, for the rotating planet, the field is conservative by some geometry tricks. We would need to imagine curved lines for the gravity vector, and that the lines are perpendicular to the blue line as well. That's not quite what I drew, and I'm sorry about that.