Umm i think u should discuss how it developed to what it is now and whats the current definition of the principle of relatively
I think u should how Galileo initially propose the theory of relatively by stating that "all steady motion is relative and cannot be detected without a reference to a outside point" - Einstien developed this further in special relatively - thought experiements with trains
Galileo proposed that time was absolute and that it was independant of all frames of references- Einstein changed this stating that light is independant of all frames of references, thus time, mass and length manipulated to compensate for this equality.
Talk briefly about time and mass dilation and length contraction as the result of special relatively
Hope that helps
