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General Formula For Reflection Direction

  1. Sep 5, 2010 #1
    An Example Scenario:

    A particle moves at 32° and collides with a wall. This wall is rectangular in nature, which means that there is both horizontal and vertical sides.

    On a horizontal tangent, it would work like this (sorry for ugly, not-to-scale diagrams):

    [PLAIN]http://img198.imageshack.us/img198/7808/questionsc.jpg [Broken]
    (reflects at 148°)

    However, on a vertical tangent it would reflect like this:

    [PLAIN]http://img808.imageshack.us/img808/2064/question2.png [Broken]
    (reflects at 328°)

    This means that:
    • On horizontal tangent: reflectionDirection = 180-incidenceDirection
    • On vertical tangent: reflectionDirection = 360-incidenceDirection

    It's lame to have two different formulas, so is there a general formula for the reflectionDirection that works with both vertical and horizontal tangents? It's fine if it uses radians instead of degrees.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 5, 2010 #2
    If the incoming angle is A, and B is an angle normal to the wall, then the reflected angle C is given by C = B - A.
  4. Sep 6, 2010 #3
    Thanks, but that was not what I was looking for.

    In case someone else needs to know, the general formula is:

    C = 180+2B-A

    Where A is the direction of incidence, B is the direction of tangent (0 if horizontal, 90 if vertical) and C is the direction of reflection.
  5. Sep 6, 2010 #4
    Well the normal and tangent angles are 90 degrees different, so it all works.

    Also, I meant C = 2B - A in my last post, sorry.
    Last edited: Sep 6, 2010
  6. Sep 9, 2010 #5
    Thanks a lot for this conversation. I was searching for this..........
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