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  1. rumborak

    I am confused about the meaning, and value, of kinetic energy

    Thanks for the replies everybody! If I understand it correctly, kinetic energy is self-consistent provided you stay in the same frame, and that my example was flawed in the sense that I disregarded the "accelerator" which would have made the total energy stay constant when taken into account.
  2. rumborak

    I am confused about the meaning, and value, of kinetic energy

    This confusion has lingered in the back of my mind for years now, would be good for me to finally get a grasp on this. Say I have an object currently at rest, and I use energy X to accelerate it to speed v. According to the standard formula, it now has a kinetic energy 1/2mv^2. Now I use the...
  3. rumborak

    Why does egg float upwards in stirred bottle of water?

    For the second video I think it might also have something to do with the fact that the vessel bulges out in the middle. The centrifugal force will naturally make it go to the widest part of the vessel.
  4. rumborak

    Detailed simulation or SlowMo of elastic collision?

    Dagnabbit, I'm in no position to make an educated criticism of what you posted :) I easily understand the parts of what you posted, but I can't say whether the conclusion you draw is logically binding. At the very least it will give me something to do on an upcoming 3-hour flight of mine. I...
  5. rumborak

    Detailed simulation or SlowMo of elastic collision?

    That's all true. Somehow I still have a hard time imagining even a theoretical setup in which *any* object, entirely within Hooke's Law's bounds, would come out with zero ringing. Negligible amount, maybe. Entirely? Somehow I doubt that.
  6. rumborak

    Detailed simulation or SlowMo of elastic collision?

    That's interesting though, because the golf ball exhibits exactly that "ringing" I was talking about (it keeps deforming after it separated from the wall). Clearly this wasn't a purely elastic collision because part of the energy is now used in that ringing. Interesting question: usually energy...
  7. rumborak

    Detailed simulation or SlowMo of elastic collision?

    Actually, when I think about it, this reflection at the end of the rods is probably the classic "closed end" wave reflection where the phase reverses. Meaning, the compression turns into expansion and travels backwards through the rod, as you mention. I'm still a bit surprised that no energy...
  8. rumborak

    Detailed simulation or SlowMo of elastic collision?

    I was thinking about Newton's Cradle the other day, and I wondered how those collisions actually look like in detail. Which then got me thinking that my understanding of even a basic elastic collision of two macroscopic objects is weak to say the least. Simplified, the two objects could be two...
  9. rumborak

    Is there any proof to show that gravity works at the Planck length?

    From a simple Occam's Razor perspective, one should first assume the laws apply at all scales. Because otherwise you might as well start checking whether gravity works behind your house.
  10. rumborak

    Velocities when generating an Archimedean spiral trajectory

    Since the usual definition of the Archimedes Spiral takes the angle as the input, it means you choose the angular velocity ω. Regarding linear velocity, I don't have an exact formula at hand, but since it gets closer to a circle with increasing angle, the linear velocity will asymptomatically...
  11. rumborak

    A Question about Loudness of Sound...

    True. Why would you think that? Keep in mind that with a bigger source surface, there are many more paths from the source to a given spot on the eardrum. Those all add up.
  12. rumborak

    Directional conservation problem with E=cB?

    Yikes, no, that is entirely the wrong conclusion. c is a proportionality factor and has no inherent direction. A wave will travel with a speed of c in a certain direction, but that is different. Regarding the phases, here another link...
  13. rumborak

    Directional conservation problem with E=cB?

    I had to refresh my memory a bit by reading up. Your link is correct, but also misleading in the text. By not considering a phase shift between the solution for the E field and the B field (eq 5 and 6), thus effectively setting the phase shift to 0, they consider only what's called a linear...
  14. rumborak

    Directional conservation problem with E=cB?

    Do you have a reference for your formula? If memory serves me correctly, there is a 90-degrre phase difference between the E and the B field in an EM wave. That would seem to directly disagree with your formula.
  15. rumborak

    Potential energy and equilibrium

    I stand corrected, I apologize. As nugatory points out, it's a question of reference point, and I guess in the case of gravity the usual reference point is taken as infinitely far apart, and thus the potential energy can only decrease from the zero point.
  16. rumborak

    Potential energy and equilibrium

    Who says so? It doesn't even make sense since there is no such thing as negative potential energy.
  17. rumborak

    Expected decay time of a sound based on its relative volume?

    Wow, ADSR. My Commodore 64 had those!
  18. rumborak

    Expected decay time of a sound based on its relative volume?

    Are you familiar with exponential decay? That's usually what's being used.
  19. rumborak

    Levitating a metal ball

    You would probably end up with a liquid ball as well, as inducing constant eddy currents to keep it levitated will cause it to heat.
  20. rumborak

    Levitating a metal ball

    Maybe the easiest way to levitate is by a steady airflow from below, like they do with ping pong balls.
  21. rumborak

    Energy shield for car

    Thing is also, from a certain distance on, the tires are a much more feasible option to achieve constant deceleration. That is, it's probably a much more fruitful avenue to try to engage the brakes earlier. That's what all these intelligent cars do of course.
  22. rumborak

    Energy shield for car

    It wouldn't need to be an airbag either, since airbags are mostly used to not crush the driver's face. Since this device would operate on the car's body, it could be as simple as an extending bumper. EDIT: Now I want to rewatch the "Herbie" movies :smile:
  23. rumborak

    Energy shield for car

    I think those adjectives already apply to a car in motion, so .... :)
  24. rumborak

    Energy shield for car

    Well, you could instead do a "proactive reactive" protection, i.e. upon sensing an incoming collision, the car could send out something (air, foam, whatever) that would enable it to decelerate over a greater distance.
  25. rumborak

    N-body random peak velocity of passing particles

    It really depends what you're trying to get out of your simulation. If the goal is just something that looks reasonably convincing, then yeah, shortcuts like capping the force etc are totally fine. However, often those shortcuts send you into a one-way street that is hard to get out of when you...
  26. rumborak

    N-body random peak velocity of passing particles

    Here's a much more straightforward example: One proton is at rest, and another proton is flying straight at it, at 1 m/s speed. And currently it's 1m away. If you choose your time resolution to be 1 second, you find that at your next time step (i.e. 1 second later), the photon is *exactly* on...
  27. rumborak

    Doubt with rotating body and force

    Do you think you can create a pic? I'm not sure of the setup.
  28. rumborak

    N-body random peak velocity of passing particles

    Yeah, step size is a huge factor in these things, and often decide whether you have a reasonable simulation, or particles flying off the screen at ridiculous speed.
  29. rumborak

    N-body random peak velocity of passing particles

    Simulating these things is notoriously tricky because you keep accumulating errors over time. One thing I can suggest, presuming you are developing this simulation yourself, is to switch from a global "grid clock" to a "particle clock" whose resolution you can adjust for each particle. If a...
  30. rumborak

    A climber hanging on a rope versus falling and being caught by the rope -- break strength?

    One thing that probably needs to be pointed out is, rope has a certain stretch *per unit length*. That actually means, by the very nature of the activity, the higher from where you fall, the more rope you fall on, which in turn means it gives more. So, long falls don't necessarily mean more...
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