COORDINATE SYSTEMS

Galileo discovered through the law of inertia that there is no single preferred reference frame. To use this discovery most efficiently, we need to discuss some geometrical ideas. The first kind of geometrical construction we need is a way of describing where things are.

If the world were only one-dimensional, everything would be on a single line. To describe where something is on that line we would first pick a point on the line as a point of reference, the origin. Then we would pick a direction along the line as the positive direction – let's say to the right of the starting point. And having made those choices we would only need to give one number – call it the x coordinate – to specify the location of a point.