Recent content by Messiri

  1. M

    Conditions to be Picked Up By Radar

    What are the conditions that must be satisfied for an object to be picked up by radar? For example, what size must objects be in order to be picked up? Do they need to have certain physical/chemical properties in order to be picked up? Can non-metallic or organic substances like humans be...
  2. M

    Floating and Sinking in a Liquid

    Anything that would make it sink. Essentially my question is...if I have a (lets say metallic container) is there a liquid that can make the container float in water (or other liquid)? Basically, what relation between the two media mentioned above (that don't include air) determines...
  3. M

    Floating and Sinking in a Liquid

    This seems to be a relatively simple question, yet I'm not sure of the answer. A balloon filled with helium gas floats in air. If I submerged a balloon or container in a liquid (e.g. water), is there a liquid with which I can fill the container so as to make it float to the surface. What kind...
  4. M

    Earth's Rotation and Frames of Reference

    What causes air to rotate with the Earth?
  5. M

    Earth's Rotation and Frames of Reference

    I have a question about Earth's rotation around its own axis. Earth rotates at around 1000 miles per hour. However, if I stand in an open field and let a balloon float beside me in mid-air, I wouldn't expect the balloon to fall away (or appear to fly away) at that speed when I let go of it. I...
  6. M

    Explaining the Difference in Charge between Particles

    Why do oppositely charged particles attract? I know this question was asked on PF a while ago, but the answers given do not seem too convincing. I understand that, by Coulomb's Law, there are attractive and repulsive forces between charged particles, proportional to the product of the...
  7. M

    Conditions for Cherenkov Radiation

    OK, so the charged particle will continue to polarize molecules until it loses energy and its velocity is at/below that of light in the medium and its energy is usually too high for it to be captured. Thanks mfb. But I'm not sure I understand what you mean by: How is the group velocity...
  8. M

    Conditions for Cherenkov Radiation

    As far as I know, Cherenkov radiation occurs when a charged particle travels through a medium at a greater phase velocity than the speed of light in that medium. Molecules in that medium are polarized and after de-excitation emit radiation. But there are a couple of things about Cherenkov...
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