Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relativistic motion

  1. Nov 22, 2008 #1
    I've always found rotational motion a little weird...

    The "odd" result is that a while a fixed linear force causes steady acceleration and an ever increasing speed with a fixed direction a fixed rotational force causes steady acceleration via a steady change in direction while speed remains constant. And that's because acceleration and velocity vectors are coincident in linear motion and offset 90 degrees with uniform rotational motion.

    But as one "silly example" of how they may be different, linear acceleration doesn't make us dizzy and that might hint at some fundamental physical difference.

    Are their any other, maybe unique, insights from special or general relativity regarding these two "types" of motion? For example the "equivalence principle" would seem to break down with rotational motion...since I think we'd sure know the difference versus gravitational effects.
  2. jcsd
  3. Nov 23, 2008 #2

    Jonathan Scott

    User Avatar
    Gold Member

    The gravitational effects of a moving or rotating body include "gravitomagnetism", which is equivalent to a rotating frame of reference and "frame-dragging" effects. "Gravitomagnetism" is related to the ordinary gravitational acceleration field in the same way that magnetism is related to electrostatic fields. In gravity, this is normally an extremely tiny effect, but Gravity Probe B has been attempting to measure it experimentally.
  4. Nov 23, 2008 #3
    Here's another insight from Fredrik in another thread:

  5. Nov 23, 2008 #4
    I am unsure of any possible differences between rotational and linear frame dragging, but they might affect light somewhat differently:


  6. Nov 23, 2008 #5
    Another aspect of rotational versus linear motion in relativity I should have remembered and posted:
    Brian Greene's explanation and diagrams showing how we move through spacetime at "c" has interesting visual distinctions between fixed velocity, and linear and rotational acceleration:
    Constant velocity is straight line in space time, acceleration is a curve and rotational motion a fixed diameter corkscrew...but I can't see a fundamental insights this provides....maybe more imagination is required!!! It also provides a rather intuitive insight into why our universe is limited to "c".
  7. Nov 23, 2008 #6
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook