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  1. K

    Help: Motivation, career advice needed.

    Well, if you are asking random people on the internet how to deal with your inner motivations, I figure that's a sign you're hard up and probably do really need to figure out how to help yourself. First, ask yourself why you got into ME in the first place. If it was because you wanted to...
  2. K

    Best vac pump for boiling water

    Could a mod, mentor, or admin please move this post to a sub-forum where it is more likely to receive a reply? Thank you
  3. K

    Best vac pump for boiling water

    Hello all, I am seeking advice on the best, relatively cheap vacuum pump to pump water vapor from the 2 kPa range to the 100 kPa range. Essentially any pump that would work well at boiling water at room temperature would work for me. I'm hoping that someone on here may have done that as a...
  4. K

    Difference between being a nuclear engineer or a physicist when working on fusion.

    In addition to GA, there are often smaller scale fusion projects in the private sector. Some of them fly under the radar, so unless you know about them, you may not hear about them. General Fusion is one of the ones that gets a lot of press recently; I don't want to broadcast the existence of...
  5. K

    Basic question on induced emf

    I think I understand now why you are having doubts. The infinitely low resistance is throwing off your physical intuition. Remember, you cannot use Ohm's Law to calculate the current in a superconductor. So thinking that a high rate of change of flux means a high induced voltage means a high...
  6. K

    Basic question on induced emf

    You are correct that the induced field in the loop will oppose the field of the magnet. However, you forget to include the fact that the magnet has moved closer to the loop, which means that there is more flux from the magnet contained within the loop (at least if you stop moving it before it...
  7. K

    Does a shrinking disk grow in the z-direction?

    If you are using a chemical reaction which has an end-product which has a higher density than the initial reactants, then some transfer of material is occurring as a result of the chemical action. Even if it is internal to the structure, there is some movement of atoms, even if only from one...
  8. K

    The impact of a punch

    Yes, in short you are correct that the impact force of a punch is proportional to the mv^2 of the arm. Of course, there are some additional small corrections that you could apply due to deformation effects. For example, the stopping displacement L is not a constant, but will increase slightly...
  9. K

    Earthquake simulation

    Basic Advice: start off with a flat surface. Use the input from the ipad to shake this flat surface in x,y,z directions. On the flat surface, construct "buildings" which are comprised of rigid body blocks of different sizes. Give each of these rigid bodies a mass - you need inertia for the...
  10. K

    Lazy Layman

    Replying as a lazy physicist, I can tell you that the answer you are looking for is here:
  11. K

    Heated coat

    A typical person puts out around 100 watts of heat energy. If you insulate that properly, you will do much better than providing a heating element. However, insulating that properly and still allowing them to breathe is the challenge. Saying that the coat is "well insulated", and then...
  12. K

    Latent Heat of Vaporization /w Temperature

    I'm not sure that the molecular viewpoint is going to be all that informative for you, because the reason has much more to do with the gas that the water vaporizes into. At 100 C, when water boils or evaporates, it turns into 100 C, 1 atm pressure water vapor. At 10 C, when water boils...
  13. K

    Electricity use:Saving by turning lights/power on/off

    Very true. I'm wondering if the original question had been posted in July if there would be as many responses talking about "free heating". Remember that if you are running your air conditioning (as some of us are right now), that every watt saved in lighting also saves about a third of a watt...
  14. K

    Maximal velocity of atoms

    It would first help to know if you are looking for a velocity achieved here on earth or if astronomical sources count. I don't know if they are the fastest ions on earth, but beam injection linacs at CERN or Fermilab routinely use beams of negative hydrogen ions in the hundreds of MeV range...
  15. K

    Falling superconductor in a magnetic field

    I think that it is okay to switch the frames of reference so that the superconductor is moving and the magnet is not. Since we are simply considering forces it doesn't really matter which of the objects is accelerated. However, there is one other big difference between the a sample of...
  16. K

    Heating a chrome roller

    The real question should be, what heat flux do you need? The roller is rolling something, and I presume that it is transferring heat to what it is rolling. In addition, it is also losing heat to the ambient air. Depending upon how and why you are transferring heat, most of your heat energy...
  17. K

    Falling superconductor in a magnetic field

    Hello. Recently I have been inspired by the classic "drop a NdFeB magnet down a copper tube" demonstration, and I have been thinking about a superconductor falling in an ambient magnetic field. I want to determine the terminal velocity, if one exists. Now, I'm interested only in the effect...
  18. K

    Generating MIST from still water

    The amount of energy it takes to turn a big lumpy mass of water into a mist depends upon how fine of a mist you are talking about. The energy is required to increase the surface area, because of surface tension. You want to use surface tension instead of Van der Waals Eq. A typical floating...
  19. K

    Slow Burning Antimatter

    If you are looking for "slow burning anti-matter", you could use an anti-matter producing isotope as your "containment system". An example would be Flourine-18, which is commonly used in PET imaging. F-18 decays by positron emission with a 1.8 hour half-life. Maybe you could make your monster...
  20. K

    How fast does a bullet return to earth?

    Regarding the possibility of the bullet breaking the sound barrier in its fall - it is possible for objects to break the sound barrier while falling - just ask Joe Kittinger (google if you don't know who he is). However, of course, he exceeded the sound barrier at a very high height, where the...
  21. K

    Rotating disk

    Sorry for taking such a long time to get back to this thread. The "resultant motion" is simply the motion which results from the combination of the spinning plus the linear motion. So Vr=Vs + Vl (for any point on the disk) Remember that velocities are vectors, so use vector addition...
  22. K

    Rotating disk

    Halls of Ivy - I believe the questioner meant "pushed so that it has an initial linear velocity of v". That would make sense. Jaweibuch - I think the best way of treating this problem is to look at the radial motion and the linear motion separately. Somebody out there correct me if these...
  23. K

    What happens to moisture when air compressed?

    I believe you are correct. The pressure of the air has no influence upon its ability to hold water (unless you are squeezing it an awful lot), however the temperature has a very strong effect. Compressing a gas willl heat it up, allowing it to pick up more water, which will condense when the...
  24. K

    Please guide me to study Physics in USA

    Red Emotion, I have gone to school in the USA, however, since I was born here, I can't give you very good advice about how to get into the US. However, I do know a bit about how to study physics in the US when you are poor. The hardest part for you will likely be getting your...