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Galilean Relativity, formulated by [[Galileo Galilei]], is the theory that was most widespread before [[Einstein]], and formed part of the basis of [[Newtonian mechanics|Newtonian Mechanics]].<ref>http://www.wolframscience.com/reference/notes/1041c</ref>

Galilean Relativity, formulated by [[Galileo Galilei]], is the theory that was most widespread before [[Einstein]], and formed part of the basis of [[Newtonian mechanics|Newtonian Mechanics]].<ref>http://www.wolframscience.com/reference/notes/1041c</ref>

== Inertial Frames ==

== Inertial Frames ==

Like Einstein, Galileo postulated that the laws of physics remain the same for observers in all inertial (non-accelerating) frames of reference. That is to say that for two bodies moving at different (but constant) velocities, it is impossible to make an absolute determination as to whether one is moving and the other stationary. All that can be determined is their relative velocity.  The thought experiment that Galileo used was to consider a passenger in the hold of the ship on a calm see, who cannot look outside. There is no experiment that he can perform within the hold that will allow him to determine whether the ship is moving or not.<ref>http://www.scribd.com/doc/51240234/10/is-for-Salvatius%E2%80%99-Ship-Sailing-along-its-Own-Space-Time-Line</ref> He formalized the idea as follows:

Like Einstein, Galileo postulated that the laws of physics remain the same for observers in all inertial (non-accelerating) frames of reference. That is to say that for two bodies moving at different (but constant) velocities, it is impossible to make an absolute determination as to whether one is moving and the other stationary. All that can be determined is their relative velocity.  The thought experiment that Galileo used was to consider a passenger in the hold of the ship on a calm see, who cannot look outside. There is no experiment that he can perform within the hold that will allow him to determine whether the ship is moving or not.<ref>https://www.scribd.com/doc/51240234/10/is-for-Salvatius%E2%80%99-Ship-Sailing-along-its-Own-Space-Time-Line</ref> He formalized the idea as follows:

<blockquote>

<blockquote>

''Any two observers moving at constant speed and direction with respect to one another will obtain the same results for all mechanical experiments.''<ref>http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html</ref>

''Any two observers moving at constant speed and direction with respect to one another will obtain the same results for all mechanical experiments.''<ref>http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html</ref>