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Janus last won the day on July 21

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  1. Soap helps remove oils and other substances which water alone doesn't mix with. Using water alone will leave these oils and the bacteria clinging to them behind. Soap acts as a go-between which allows the water to grab on to and remove the oils.
  2. Implications of movie physics

    Drag force varies by the square of the velocity. It also depends of the drag coefficient for the bullet, which, at high speeds, will also vary with speed ( in a very non-linear way for example, with the bullet I'm considering the Cd stays constant from 0- mach 0.4, falls between M 0.4 and M 0.9, rises steeply to a maximum from M 0.9 to M 1.1, and then slowly declines past M 1.1) Using the numbers for a 9mm, 19.44g, very low drag bullet, traveling at mach 1.1, I get a deceleration of ~10 m/sec. It would be decelerating at the same rate at which it was falling.
  3. gray hair

    It seems to be the result of two factors; The reduction of pigment production, and the natural Hydrogen peroxide in your hair follicles which builds up over time and acts as a bleaching agent.
  4. According to one study, ape have less grey matter in their spinal cord. This leads to fewer neural connections to the muscles. Basically, a single nerve impulse triggers more muscle fibers than it does for humans. This gives ape more brute strength. The greater amount of grey matter and larger number of neural connections human have means each nerve impulse controls a smaller group of muscles. While this reduces the strength potential for humans, it increases their fine motor skills. Apes are strong, but are poor at doing delicate tasks, while humans are not as stronger but are capable of doing all sorts of delicate tasks. It's a trade off between fine muscle control vs. pure strength. You just can't "have it all". Even in your post about breeding faster and stronger humans. The truth of the matter is that you would likely be forced to choose one over the other. People genetically disposed to be great weight lifters aren't going to be particularly fast on the race track, and a great marathon runner isn't going to excel at the clean and jerk. You probably would even have to qualify what you mean by "fast"; a good sprinter isn't going to fare well as a long distance runner and vice versa. For one thing, muscle fibers come four types that are categorized by their "twitch speed" and fatigue factor. Type I is a slow twitch fiber. It doesn't contract as fast but has good endurance as it also doesn't fatigue quickly Type IIA is a fast twitch fiber. contracts quickly, but fatigues rapidly also. Type IIB is a combo, doesn't twitch as fast as IIA, but doesn't fatigue as quickly either. Type IIC fastest response, but fatigues the easiest also. What separates these types of fibers is where they get their energy. Type I gets it aerobically (by using the oxygen we breathe) Types IIA and IIC get it anaerobically (using stored energy sources which deplete rapidly) Type IIB uses a mixture of both. A good sprinter might have an abundance of Type IIA, while the long distance runner might have an abundance of Type I.
  5. Why doesn't jupiter explode?

    Hydrogen fusion, the process by which the Sun generates requires special conditions, as pointed out by chenbeier.( which is why we are having such a hard time developing fusion power plants. Even our hydrogen bombs need a fission bomb as a trigger). It is estimated that you would need something between 70 and 80 times the mass of Jupiter to maintain fusion at the core. Comets hit the outer atmosphere of the planet where the gases are even more rarefied. While these comets could provide the energy needed to ignite chemical combustion, Jupiter's atmosphere isn't combustible. For that you need something the burn (in this case the hydrogen), and something for it to chemically react with (like oxygen). Jupiter's atmosphere has plenty of the first, but is too deficient in the second to support such combustion.
  6. By what you would visually see, then yes, you would see events occurring faster at Andromeda. Though you couldn't actually travel at the speed of light, just close to it. The equation for this relationship is fo = fs sqrt((1+v/c)/(1-v/c)) Where fo is the observed frequency, fs is the source frequency, and c is the speed of light. Note that if you make v=c then you end up with fo = fs sqrt(2)/0) And the division by 0 is undefined. ( but since travel at the speed of light is not allowed, this never arises.) However, just because you are seeing events unfold more quickly at Andromeda, does not mean that you would conclude that they were unfolding faster. Once you account for the effect caused by the decreasing distance between you and Andromeda, you would conclude that events were actually unfolding slower at Andromeda. For example, if you were traveling at 0.99c, you would see events at Andromeda as happening 14 times faster, but would conclude that they were happening 7 times slower. The 7 times slower would be due to time dilation, while the 14 times faster you see is due to Relativistic Doppler effect, which is a combination of time dilation and the effect caused by the decreasing distance. Even this is only a part of the whole picture. In order to understand what happens over the whole trip from Earth to Andromeda according to both Earth and ship would involve delving more deeply into Special Relativity.
  7. Technically, I would be hesitant to call a radioisotope thermoelectric generator a reactor. As you noted, it depends on heat of decay rather than a fission reaction. The main concerns for choosing an isotope in this case is its half-life and, in the case of spacecraft, it's power to density ratio. This, in turn, can depend on the mode of decay. Alpha decay is more energetic than beta decay. Thus Plutonium-238 is a good choice for a space probe, while Strontium-90 would work in cases where you aren't as concerned with the mass. (The former Soviet Union used Sr-90 RTGs to power some remote lighthouses and navigation beacons)
  8. With a typical nuclear power plant, the fuel has been enriched to 3.5% - 5% To make a reactor as small as the ones they use in submarines, they have to enrich the fuel to as high as 90%, which is weapons grade. So you can make relatively small reactors as long as you are willing to produce and deal with such high grade fuel. You still have to have enough fuel to maintain the reaction while keeping it spread out enough to allow you to control the reaction with control rods. So even with high grade fuel, there would be a minimum size for a reactor.
  9. How do devices read electromagnetic signals?

    A simple diagram of an ADC would look like this: The eight output lines each output a 1 or 0, Together they can output binary numbers from 00000000 (0) to 11111111(255). The input is compared to a reference voltage and converted to an output value depending where the input is compared to the reference. There would also be a "clock" input. This is a signal that tell the ADC how often it should sample the input and change the output values.
  10. Truth About Corners

  11. Swallowing spider silk dangerous?

    And even if it weren't digested, it would just pass through your digestive system and be eliminated as waste.
  12. Why does this ball go faster than c?

    if the ether the M&M experiment was trying to measure the Earth's drift with respect to existed, then, yes there would have been a slight offset in the perpendicular light. (with the 11 m path length, and a "drift velocity of 30 km/sec, it would have only amounted to a bit over 1 mm.) This would not however have effected the time it took for the perpendicular light to travel it path, and it was the timing or phase difference the experiment was designed to measure. However, the M&M experiment, and those following it, failed to detect said ether. No ether, no drift. Thus "moving" or "stationary" the beam travels at a 90 degree angle to the apparatus. If I'm playing catch with someone across the width of a railway car traveling at 60 mph relative to the tracks, I don't have to "lead" him with my toss. I toss the ball directly at him. Light in a vacuum behaves the same way, as long as the target has no velocity relative to me, I just aim my light at the object.
  13. Simple question?

    So for example, starting at the surface of the Earth, a graph of escape velocity would look like this:
  14. Which is exactly what people have been doing here; Entertaining your idea, but then ultimately rejecting it.
  15. The Moons Atomosphere

    When there is a wind the pressure is greater on one side (windward ), than it is on the other. Air pressure is just the sum of collisions of air molecules. With a wind, the particles are hitting with more force on the windward side. This also causes a wind shadow effect which lowers the air pressure a bit on the leeward side. Gravity does not "hold you in place", it pulls down on you. It is the friction between the object and the surface it is resting on that keeps it in place. If you to remove the friction, an object on a level surface would start sliding around at the slightest touch, regardless of how strong the gravity was. Gravity only fights efforts to raise the object against its pull. Gravity on the moon is determined by the same considerations as gravity everywhere: the mass of the objects involved and the distance between them. For a body like the Earth, your effective weight at different points of the surface are mainly effect by the fact that it's surface is not a perfect sphere, which alters the distance from the center, and the slight centrifugal effect caused by it rotation. But both of these only result in small variations. For the moon, these same variations would apply. But being both a smaller body, and spinning 1/27 as fast as the Earth, the centrifugal effect will be much smaller, and you would get a smaller variation between pole and equator.