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2.2.5 Coordinate Systems and Frames of Reference

Since the era of Galileo, it has been the custom of physicists to illustrate reports of experiments with drawings of the relevant apparatus. Over the years, these simple diagrams have evolved to include the geometrical space environment of the processes involved. These 'Frames of Reference' usually provide a coordinate system which allows each point in the geometric space to be uniquely specified. It is important to appreciate that coordinate systems are imaginary, and exist as mathematical objects. They are not a property of space.

In most cases the geometrical environment is flat, two or three dimensional space, and the coordinate lines consist of rectangular grids intersecting at right angles. If the process is time dependent, then one of the axes of the space may be time, which strictly speaking is not a geometrical property. It is necessary that the coordinate system employed is suited to the curvature of the space being represented. For example, the surface of a sphere cannot be represented by a grid of straight lines. In the case of planet Earth, a system of curved lines is used, which are known as the lines of latitude and longitude.

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