Omega Centauri

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visits member for 3 years, 9 months
seen Nov 21 '11 at 22:43

Nov
12
awarded  Yearling
Nov
12
awarded  Yearling
Oct
7
awarded  Nice Answer
Sep
21
awarded  Nice Answer
Nov
12
awarded  Yearling
Oct
25
answered If you stop water from expanding, will its temperature stop rising?
Oct
18
answered why making a surface “super” smooth increases the coefficient of friction?
Oct
11
comment Remnant of a supernova
Should we really call a supersonic shockwave a sound? Or should sound be reserved for wave amplitudes that are still in the linear regime?
Oct
7
comment domestic electric AC wiring - Live and Neutral correct or not?
In normal operation the "neutral" should be within a few volts of ground. But, for safty sake, don't count on it. In an abnormal situation, say a short in the transformer, or somewhere else in the system, it could potentially become live. Thats why the standard is becoming the three prong plug, (live/neutral/ground), the later can be connected to say a tools outer casing, to insure that a short cannot electrify the casing. Using the neutral for such a purpose is not guaranteed.
Oct
5
answered How does a change in temperature affect relative humidity
Sep
28
comment What is changing in latest light bulb technologies?
Here in the US the phaseout is being slowly staged (but politiv=cally demogouged just the same). Initially only 100watt bulbs are banned (fro sale), then the wattage limit for old tech incandescents is decreased in stages. There is a sort of "high efficiency" incandescent that can still be sold, I think the filament has a special coating the decreases its IR emmisivity, they are about 30% more efficient than the old bulbs. The new kids on the block are the LED bulbs, which are coming down in price and up in quality.
Sep
15
comment Pressure at a given altitude?
The formula is only good in the troposphere. The troposphere is a convective layer, so the temperature is approximately governed by the adiabatic lapse rate. Above that, the temperature is higher, bacause of radiative effects (mainly absorption of solar UV). Note the power law formula has a finite hight atmosphere, at which point both pressure and temperature reach 0K. Obviously that would violate thermodynamics. The constant lapse rate is only (approximately) true in the convective part of the atmosphere.
Sep
14
comment Why is the energy density of gasoline so high?
The energy density of hydrocarbons does vary. IIRC diesel fuel has higher energy density than gasoline (higher molecular weight equals more carbon versus hydrogen), ethanol has less.
Sep
13
comment Why is the energy density of gasoline so high?
Some note of caution. Gasoline, by itself (unlike some chemicals that can undergo exothermic decomposition like explosives) doesn't actually contain energy. It is only on chemical combination with Oxygen, that energy is released (converted) to heat. Per atom, IIRC Calcium and Florine have the strongest bond. Also some atoms (as opposed to their more normal bi-atomic molecules, such as atomic Hydrogen and Notrogen give off a large amount of energy when they combine into the molecular form). Of course these are generally not stable.
Aug
31
answered Heat in the car during sunny day
Aug
31
comment What happens when a lightning rod is not earthed?
I wouldn't say it doesn't work at all. At least in the context, that pre-bolt, is affects the voltage distribution, and hence affects where the lightening strikes, and where the current flows afterwards. But you are correct, that the current (assuming the bolt strikes the conductor), must then flow from the conductor to ground. It is likely to take one or more pathways to do that, and the results may be unfortunate.
Aug
29
comment Can pockets of air exist underwater?
@Peter. And if they are old, I wouldn't expect the same relative concentrations of gases. It might be gas, but it might not be good to breathe. I could imagine a cave, where the air is renewed only at low tide, perhaps only a rare very low low tide. I wonder what sort of composition that air would have. Near the surf zone, is bubbles/foam are advected to your "bubble" they could also contribute.
Aug
23
comment Why is radiative forcing from CO2 logarithimic and not a decreasing exponential?
Full computer simulation is what I meant, by using a radiation transport code (on a model of the atmosphere). The lineshape arguments like most back of the envelope arguments, are useful for building intuition, not so much for final results.
Aug
22
comment Why is radiative forcing from CO2 logarithimic and not a decreasing exponential?
I believe that covers the basic physics, its the line shapes that lead at first order to a log dependence of forcing. Of course the planetary scientists and climatologists, run more sophisticated radiation transport models, and have curves for forcing versus concentration (which does depend upon other atmospheric components as well). These curves can be fit to forcing versus log of concentration, and are roughly linear in the earth climate relevant zone. I believe the forcing is known to roughly 10%.
Aug
22
comment Explain the direction of waves on sea shore
Waves do transmit energy downwind. So waves going away from shore that are generated by wind, don't have any fetch to generate waves heights. So the amplitude of these waves should start at zero at the shoreline, and increase as you get further from shore. Also nore for incoming waves, the are diffracted as they reach shallower water -they wave velocity if lower as the water gets shallower, so this means obliquely incoming waves appear to be mostly coming in perpendicular to the shore.