The Physics Hypertextbook

How many capacitors have you seen rated for over 100 MV (megavolts)? I think a dielectric that can survive a field with that much tension is called unobtanium. Lightning is causing dielectric breakdown of the air (a great insulator already) over thousands of meters. https://hypertextbook.com/facts/1998/MathieuLo.shtml

> How much liquid contaminated waste can we put into the ocean? A lot. The Wikipedia article [1] quotes a flow rate of 400 tons per day. Let's suppose that that flow rate was maintained for 30 years, a typical reactor lifetime (which is far longer than anyone is claiming a flow of contaminated waste from Fukushima). That comes to 400 * 365 * 30 = 438,000 tons of contaminated water, or 4.4 x 10^8 kg. According to the Physics Factbook, the mass of water in Earth's oceans is about 1.3 x 10^21 kg. So 30 years' worth of contaminated water from Fukushima amounts to about 0.3 parts per trillion of contaminated water in Earth's oceans. That's not even comparable to naturally occurring trace radioactive elements. [1] https://en.wikipedia.org/wiki/Fukushima_disaster_cleanup#Radioactive_c… [2] http://hypertextbook.com/facts/1998/AvijeetDut.shtml

I'm not sure why you'd think it's a stupid question (what is a stupid question?) -- but according to the Internetz[1,2], I think the answer is no. The difference of pressure between an soda-can and air (at ground level) would appear to be between to and three atmospheres worth (or like sea-level and a depth of 20-30m/~60-90', if the rule-of-thumb I've learned is about correct; see also: Why is parachuting into water OK, while diving and then flying a bad idea?). It would appear the interior and exterior and an air-plane typically differ at about half an atmosphere (5m/15' water). [1] http://hypertextbook.com/facts/2000/SeemaMeraj.shtml [2] http://en.wikipedia.org/wiki/Cabin_pressurization

"Einstein's greatest role in the invention of the atomic bomb was signing a letter to President Franklin Roosevelt urging that the bomb be built." http://hypertextbook.com/eworld/einstein.shtml where he cites the work made by Fermi el al. The first artificial nuclear reactor was built in 1942 (http://en.wikipedia.org/wiki/Chicago_Pile-1) Einstein's relativity theory and the equivalence of mass and energy is commonly cited has having laid the ground for the exploitation of the energy from nuclear decay, but I have the feeling that research in the nuclear energy field would have continued and yield some interesting results even without knowing that E=MC^2 beforehand.

I saw that page and went 'really'?? http://www.scribd.com/doc/15911579/Derivation-of-Fundamental-Particle-… From that article, the ratio Rp to Re is about 83. But the more I look, the more answers I find. Scienceworld has 0.80+ fm for the proton, is silent on the electron. Comparing the following two (Physics Factbook), they could be about equal. "The electron is a point-like particle-that is, a particle with no measurable dimensions, at least within the limitations of present-day instrumentation. " http://hypertextbook.com/facts/2000/DannyDonohue.shtml http://hypertextbook.com/facts/1999/YelenaMeskina.shtml Doesn't nullify the point that atoms are empty space - but comparing radii is risky business.

Below is a table of elements used, ordered by boiling point. Beryllium has the lowest boiling point at 2742K. Zirconium has the highest melting point at 2125K. This means the furnace temperature was greater than 2125K. TIG temperature can easily reach 3000C (close enough to 3000K) [1], more than the boiling point of beryllium. The temperature of the metal slug would rise until it reaches thermal equilibrium through heat loss, the energy loss likely being due to the vapourisation of the element with the lowest boiling point: beryllium. That smoke was probably beryllium vapour. I'm no expert, but I would assume the beryllium vapour would not have made it out of the apparatus. By luck, it would have condensed either before reaching the HEPA filter or on its way through the HEPA filter, even though the HEPA filter was not designed to stop a vapour. Nile Red also had the sense to use a fume cupboard. Despite this, the inside of the apparatus could well have been coated with friable condensed beryllium, which would probably not have been flushed by the argon. If doing this, I'd take additional precautions against condensing beryllium vapour containing the equipment (I don't know what they might be). Maybe it's a case of controlling arc temperature to keep it below the boiling point of beryllium? Maybe a small amount of impurity with a lower boiling point can be added to the mix, so it boils off first and avoids the beryllium boiling? This might also prevent loss of…

It's exceedingly slow. Neurons fire at not 4 gigahertz, 400 megahertz, 40 megahertz, 4 megahertz, 400 kilohertz, 40 kilohertz, 4 kilohertz, or 0.4 kilohertz (400 hertz.) They fire at < 1 hertz to about 200 hertz. [1] That is literally 8 orders of magnitude slower than processers. 8 orders of magnitude is the size of difference between a grain of sand and 1.2 short tons. In the time that your neuron moves 1 grain of sand, a computer can move 1.2 short tons worth of sand 1 grain at a time (talking about just cache here) - because it's switching at 4 GHz instead of 10 hertz. That is enough to make a lot of back and forth trips. Now, you have to make a lot of these back and forth trips because the brain is extremely parallel. But the difference between these extremely slow biochemical firing speeds and gigahertz light speed enables this. The speed of propagation in the brain is about 100 meters/second [2]. The speed of propagation between two fiber optic end-points is about 299 792 458 meters/second. That gives you 7 orders of magnitude to play with. Or, in other words, it can let you take seven orders of magnitude more trips across a data center (or go that much farther) before you miss a real-time deadline for when you need to address a neuron by. In the future it's pretty clear that computers are not going to think as fast as the human brain when doing similar calculations using a similar topology, but, for example, 10,000 times faster than real-time. This…

"Hey, 98.6, it's good to have you back again... " One of the best-known numbers in biology came about due to a similar confusion over significant figures: > The first systematic measurements of human body temperature were performed by the German physician Carl Wunderlich. In 1861 he measured the temperatures of one million healthy individuals (a sample size that seems too large to be believed). The average value was reported as 37 degrees celsius. When converted this value becomes 98.6 degreed fahrenheit. So what's the problem? Wunderlich's value has only two significant figures while the converted value has three. The last digit (the "point six" at the end) should be regarded with great suspicion. Wunderlich's converted value should really be stated as "ninety eight point something" if one is being honest. Actually, if one is being honest and respecting the usual rules, it should be stated as 99°F; that is, rounded to two significant figures. (And, of course, we're not that simple: Core body temperature rises and falls naturally due to a number of factors even when we're completely healthy, so any single number as "the" healthy body temperature is, strictly, incorrect.) http://hypertextbook.com/facts/LenaWong.shtml

I used to have high hopes for fusion power until I came to learn two things: 1. Neutrons rapidly destroy any kind of containment. He-3 is seen as some kind of holy grail here. Unfortunately it's incredibly rare. The best source is probably the Moon (which, with no atmosphere, has had billions of years of solar winds to collect non-trivial amounts of He-3); and 2. To sustain a fission reaction any current research reactor I can recall reading about uses probably radioactive isotopes (most likely tritium ie H-3) or at least somewhat uncommon isotopes (ie deuterium, H-2). Fun fact: per cubic foot compost generates more power than an equivalent volume of material from the Sun's core [1]. What makes stars such great energy producers isn't fusion per se, it's their sheer size and fuel supply. Fusion goes hand-in-hand with the Utopian concept of "free energy" because obviously water (and thus hydrogen) is abundant. But no energy will truly be "free" although it may be cheap enough to have the almost the same impact as being free. There are four component costs in energy: 1. The cost of building a device that produces energy; 2. The cost of maintaining that device; 3. The R&D required to bringing that device to market. Obviously, over time, this cost diminishes to zero; and 4. The cost of extracting, storing and transporting whatever fuel is required. So for hydrogen, assuming a fusion reactor doesn't use sea water, you must first extract hydrogen. This is actually…

When you think about it it's astounding how much energy this technology consumes versus a human brain which runs at ~20W [1]. [1] https://hypertextbook.com/facts/2001/JacquelineLing.shtml

Gasoline has 45 MJ/kg for comparison so it is a ten times that of TNT. Source: https://hypertextbook.com/facts/2003/ArthurGolnik.shtml

https://hypertextbook.com/facts/2003/ShaniChristopher.shtml Spontaneous ignition temperature for gasoline vapour listed as 280C, well below "red hot".

> for gold to be used, resistance to corrosion must be important. from google, copy pasta: "Gold plating is the deposit of a thin layer of gold metal on a substrate, typically in the 0.25 – 5 micron range (0.00001”-0.0002”)." Not a lot of gold is used in plating the business ends of an RCA cable or TRS connector. Al, yes, more copy pasta: "Aluminum has a very high affinity to oxygen. When a new aluminum surface is exposed in the presence of air or any other oxidizing agent, it quickly develops a thin, hard film of aluminum oxide (or hydrated oxide in non-stagnant water). This aluminum oxidation is precisely what makes aluminum so corrosion-resistant." But I doubt the thin, hard film of aluminum oxide conducts as well as gold. Nope.[1] [1] https://hypertextbook.com/facts/2006/EuniceHuang.shtml

Obviously by "density" we mean weight divided by volume. Here is a collection of four textbooks that all agree on the 1.4 figure. https://hypertextbook.com/facts/1999/MayKo.shtml

Microwave ovens, the other source of 2.4GHz. There's probably a reason they used 2450MHz as the test frequency, a magnetron from an oven is cheaper and easier to obtain. https://hypertextbook.com/facts/1998/HowardCheung.shtml

Earth rotates at 1670 kilometers/hour, the Moon travels at 3,683 kilometers per hour, tidally locked to Earth so the telescope travels at that speed. However, the Moon has a lot further to travel so a more meaningful measure is change in angle over time. For the purpose of a "long exposure" the Moon would have a lot less smear. Earth: 7.2921159 × 10−5 radians/second (sidereal, not including solar orbit, at equator) Moon: 0.2.66169 × 10−5 radians/second (on average for its eliptical orbit) https://hypertextbook.com/facts/2002/JasonAtkins.shtml https://www.quora.com/What-is-the-angular-velocity-of-the-moon-in-its-…

On https://hypertextbook.com/facts/2003/IradaMuslumova.shtml, the highest estimate there is 5W, and that’s an outlier on that page. That may be because of the difference between output power and input power needed to produce it. One citation there says the mechanical efficiency of the heart is about 20%.

120 MJ/kg for H2 vs 46 MJ/kg for gasoline. Both are explosive, so I think (I'm no authority on this) we can compare those values directly, without taking into account the storage pressure. Source: https://hypertextbook.com/facts/2005/MichelleFung.shtml https://hypertextbook.com/facts/2003/ArthurGolnik.shtml

Had to look this up because I was curious. This site quotes from the World Almanac, which states 32% of the US had a cell phone in 1999. https://hypertextbook.com/facts/2002/BogusiaGrzywac.shtml From my personal anecdotal experience, that would be correct. I had a cell phone, but had gotten my first in 1998. All of my friends who were professionals did too. My friends who were artists, or more marginal economically, did not. Cell phones were a common sight, but it was also clear that many didn't have them. I remember feeling slightly special when I could pull mine out in 1999. Even Seinfeld had jokes about cell phone etiquette. Which was a clear sign they didn't expect their audience to be entirely comfortable with them. A breakdown by city would be interesting. Wouldn't be surprised if usage was 50%+ in larger cities.

245J/5s == 49W This website [1] shows several sources. The range of estimated power outputs is between 1W and 5W. https://hypertextbook.com/facts/2003/IradaMuslumova.shtml OP hypothesis seems to be correct.

Where did you get 400+ deaths per day in NYC? That sounds really high; I bet it’s well under half that. Here’s all I could find with cursory search: https://hypertextbook.com/facts/2005/TriciaMui.shtml

> But we can't even make a sustainable replacement for it that wouldn't require 4 kilograms of external batteries that you'd need to recharge multiple times a day. There's no magical solution. The heart develops several watts of mechanical power 24/7 [1], i.e. that's what is required even if the pump was perfectly efficient, and I doubt pumps are that efficient. [1] https://hypertextbook.com/facts/2003/IradaMuslumova.shtml

Absolutely. But I read the comment as complaining about efficiencies of automobile engines, not modern military jet engines. The combustion temperature of gasoline is 553K. https://hypertextbook.com/facts/2003/ShaniChristopher.shtml https://www.quora.com/How-much-heat-does-it-take-for-gasoline-to-ignit…

I wonder how much capacity it takes to power a parking lot full of street lights vs a parking lot full of Teslas. I imagine it's a wide gap - each Tesla draws about 1.4 kW[1], while each streetlight draws 80 watts[2]. [1] https://www.pluglesspower.com/learn/tesla-model-s-charging-home-public… [2] https://hypertextbook.com/facts/2004/MarinaAvetisyan.shtml

1) Energy density matters. You cite no data to back your claims up, in fact the opposite is true. Lithium batteries pack just as much energy per kg. Lithium is at 41.7 kJ per gram [0], Oil is at 45 kJ per gram [1] Battery tech has more room for improvement than the hard chemical/physical limits of oil. 2) Job creation is a farce. We don't more oil riggers any more than we need more lamplighters and switchboard operators. If you want to ensure everyone has a good quality of life - a basic income looks more promising.[2] [0]: https://en.wikipedia.org/wiki/Lithium-ion_battery [1]: https://hypertextbook.com/facts/2003/ArthurGolnik.shtml [2]: https://tcf.org/content/commentary/universal-basic-income-versus-jobs-…

“To carry out this plan, it will take a volume of 7 cubic miles of olivine rock placed on 2% of the world high-energy, tropical shelf-seas each year.” To put this in perspective, the global annual oil production is about 1 cubic mile [1], and concrete production is about half a cubic mile [2], [3] (4.4 BN tons at 2.4 t/m3 = 1.83 cubic km = 0.44 cubic miles) [1]https://en.m.wikipedia.org/wiki/Cubic_mile_of_oil [2]https://archpaper.com/2019/01/concrete-production-eight-percent-co2-em… [3]https://hypertextbook.com/facts/1999/KatrinaJones.shtml

Path (through the body) and frequency also matter. See generally: https://hypertextbook.com/facts/2000/JackHsu.shtml I recall a story, late 1990's to early oughts, of a solo researcher found dead in his lab of apparent heart failure whilst working with very low voltage- and amperage currents, but at critical frequencies. I cannot find an online reference presently.

3% energy growth is unsustainable in the long run; at that rate we are about 1000 years from using more energy per year than the sun emits in totality: 2015 energy usage 110PWh for the entire year[1] That works out to ~1.8e13 W average power. Total output for the sun is about 4e26 W[2] This works out to about 44 doublings, and 3% growth is a doubling every 24 years which means we need to surpass Kardashev II in 1000 years. 1: https://en.wikipedia.org/wiki/World_energy_consumption 2: https://hypertextbook.com/facts/1999/MatthewTsang.shtml

Right, but if the point of planting the trees is carbon amelioration, than carbon neutral would somewhat defeat the point. I've seen this argument before, and I think the real place it falls down is that there just isn't that much space. For mature growth forest, you have something like 40-ish big hardwood trees per acre [1]. Those are, to my understanding, the only ones that are really relevant because they make up most of the biomass. Other types of trees are just a rounding error. `1.2e12 / 40 acres -> square miles` (frink) is 4.7e7 square miles. That is more than the whole land area of Earth [2]. There is certainly not enough land that would support mature forests available to plant so many trees, unless I have made a serious calculation error. [1]: http://www.sbcounty.gov/calmast/sbc/html/healthy_forest.asp [2]: https://hypertextbook.com/facts/2001/DanielChen.shtml

>if you set up a solar panel that directly feeds a resistor, you have a dissipative system that's unlikely to get hotter than the sun. I guarantee you this can be done. Arc welding [1] goes to many thousands of degrees, up to 20,000C. A square mile of solar panels will most certainly give me enough energy to power an arc welder. In fact I will probably will get away with just 100kw of pwoer, so 500 panels give or take. [1] https://hypertextbook.com/facts/2003/EstherDorzin.shtml