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B How to specify direction in 3 dimensional world

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  1. Apr 7, 2017 #1
    I have just started studying vector algebra and i was wondering how is the direction of a vector (or any point object) specified in 3 dimensions. I know how to indicate the direction of a vector in 1 dimension and 2 dimensions. Is the direction of a vector in 3 dimensions stated by using angles or is there any other way to do so?
     
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  3. Apr 7, 2017 #2

    A.T.

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    By the vector itself?

    You can represent a vector in polar coordinates, which include angles.
     
    Last edited: Apr 7, 2017
  4. Apr 7, 2017 #3

    vanhees71

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    A direction is given by a unit vector. Each unit vector can be specified by spherical coordinates, i.e., two angles. You know this from latitudes and longitudes on Earth. In physics one uses a slightly adapted version of this, which is as follows: Take a Cartesian coordinate system and specify its ##z## axis as the polar axis. Then the unit vector is given in terms of the polar angle ##\vartheta \in [0,\pi]## and azimuthal angle ##\varphi \in [0,2 \pi[## as
    $$x=\cos \varphi \sin \vartheta, \quad y=\sin \varphi \sin \vartheta, \quad z=\cos \vartheta.$$
    To visualize this, see the following figure from Wikipedia

    https://en.wikipedia.org/wiki/File:3D_Spherical.svg

    For the unit vector you have of course ##r=1##.
     
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