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J.C.MacSwell

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Everything posted by J.C.MacSwell

  1. Ah...the age old question...if I say something in the forest and my wife is not around to hear it...am I still wrong?
  2. Sooo...how did you do?
  3. Right. Also the spring is assumed massless, but fixed at one end or attached to a massive object (can be assumed infinite) that can absorb (in case of an idealized damper) or can reverse (in this case of an idealized spring) any momentum in the remainder of the system. It is always good to look at it and ask if the assumptions are reasonable for the purpose. If, say, the bullet takes any significant time to imbed, the results will be off.
  4. Thanks Doc I had read about him recently and the fact that he had more Neanderthal DNA than modern Europeans, after reading a thread in the Bio section IIRC. (might have been in speculations) Here is his Wiki page: https://en.wikipedia.org/wiki/%C3%96tzi
  5. LA, why will you not get enough sleep? I would suggest you pace your time so that you can take very short mini-breaks and get up, pace or stretch. Just make sure you are aware of whether your opponents clock is ticking or your own. You can also stand behind your chair to analyse and shift your weight back and forth...a bit of movement can help, especially if you are overtired.
  6. You are looking at radiation that has redshifted out of your visible spectrum due to universal expansion since it was sent, and toward some that is delayed to the point it will never arrive. So you are unable to observe anything in those areas of the sky.
  7. The best tournament I ever had followed a couple of nights of watching 2 very highly ranked players play speed chess (5 minutes each blitz). If there was something interesting they might quickly analyze a position from the game (they could place every piece immediately in position, even if it was 20 + moves back) but for the most part play 20 + games back to back while I watched. Somehow this allowed me to play above my level during the tournament. I assumed it was mostly pattern recognition of both openings and stronger middle game play than what I typically played. I don't believe I would have done as well if I had spent the same nights playing speed chess as I did from watching better players, given that I was equally focused. P.S. I had no beer during the tournament...if LA was wondering
  8. Frictionless is the key. It can't avoid the sides...the darn Moon makes sure of that.
  9. You might use over half, well into which time you will have been struggling, but you won't get a whole lot further before your demise. http://www.geography.hunter.cuny.edu/tbw/wc.notes/1.atmosphere/oxygen_and_human_requirements.htm
  10. What is the dew point of the air in the house vs the air outside?
  11. Assume an ideal spring. You can assume energy is conserved without dissipation from the point after the collision where the masses are then at the same velocity. You have to assume the collision was instantaneous or you will not have enough information. From the spring constant and amplitude you can for that energy. Knowing the total mass you can solve for what the velocity was at that point, just after the instantaneous collision. From that velocity and the masses you can solve for the initial velocity of the bullet, and you can also solve for the initial kinetic energy and how much energy was lost in the inelastic collision. You can also solve it by making other assumptions about the collision being not instantaneous, but it gets more complicated because the spring will displace during the duration of the collision.
  12. “Okay you guys, pair up in threes!” -Yogi Berra
  13. Just another excremental advancement in science...
  14. Thanks strange. So at anything but very close to c, they drop below a detectable level.
  15. If neutrinos (or gravitons) have a very small mass, and thereby travel "almost" at c, should there not be some pretty slow ones running around these parts, having travelled some distance while the Universe expanded?
  16. "Most facts about coincidences cited on the internet are factually incorrect, or incorrectly attributed" -Mahatma Ghandi
  17. Just announced today Feb 22, 2017 (some earlier) and "just" 39 light years away https://www.theweathernetwork.com/ca/videos/gallery/largest-gathering-of-earthlike-planets-ever-discovered-see-it/sharevideo/5333090668001 https://www.theweathernetwork.com/news/articles/nasa-announcement-exoplanets-atmospheres/79602/ http://www.sciencealert.com/nasa-just-released-travel-posters-for-our-new-sister-solar-system-and-they-re-cool-as-hell As seen from Earth all 7 of the planets in this solar system (3 believed to be in the "zone", rocky and expected to contain water/possible oceans) pass in front of their red dwarf star. (Trappist-1)
  18. That was with regard to the speed of sound. This is known for most common materials.
  19. Compare a star reacting and accelerating in response to some force applied to one side vs one simply "moving" with constant velocity Not entirely. There are differences in the bulk modulus, shear modulus, and Young's modulus of a material and they all are related to the speed of sound (or speeds of sound, as there maybe more than one type of wave propagation). But if you can imagine a pressure wave moving along a rod, there would be a different response in a bulk than at less constrained surface (the rod can expand or contract more readily) ...the lesser the width, the more that effect would be present
  20. Nothing has an infinite modulus of elasticity, and in theory nothing can. I would expect it would take very little force to shorten a light year long stick several centimetres, even using the stiffest known materials, though it might take some time. If I had to guess, I think we could shorten a 1 inch diameter, light year long stick of any known material by several miles (assuming it was constrained not to buckle), just by lightly pushing with our own strength on each end (assuming we were supported to keep pushing as it moved) before feeling any effects from the other end (many many years later) WRT the speed of gravity, recalling from previous threads on orbits, despite the lag from the distance the gravitational "force" is directed for the most part at the current positions, not the positions the bodies were in the lag time earlier.
  21. Of course...not sure why I typed that...how did the game end up?
  22. How does it look after N-c2 check instead of R-g1 stalemate?
  23. Yes. As the scale is not part of the system, the system is not isolated. Isolated, there can be no net force on the system at any point in time. So the answer would be no without interaction with the scale or some other outside force. The wheels can exert a force on the remainder of the system, only to the degree that the remainder of the system exerts an equal but opposite force on the wheels, so the momentum balance does not change without some external interference.
  24. An isolated rotating unbalanced wheel must wobble, but as per Strange the centre of mass (and energy) will not. So there is no need to look at a cycle of events where you shift an isolated systems mass/energy at one point, change something, reverse it, and ratchet yourself in any new direction...you simply can't to it at any point in the cycle.
  25. You cannot change the velocity of the centre of gravity of an isolated system. You cannot even get it to wobble, even temporarily or slightly. Not even in a thought experiment except with wrong assumptions or bad math. So if you come up with some contraption that appears like it might...you look for your error.
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