2.7 Graphical Analysis of Motion
A graph is a pictorial diagram in the form of a straight line or a curve which shows the relationship between two physical quantities. Usually, we draw a graph on paper with equally spaced horizontal and vertical lines. Generally, every 10th line is a thick line. In order to draw a graph, two mutually perpendicular thick lines xox' and yoy' are selected as the x and y axes. The point where the two axes intersect each other is known as the origin O.
Positive values along the x-axis are taken to the right side of the origin and negative values to the left side. Similarly, positive values along the y-axis are taken above the origin and negative values below. Normally, the independent quantity is taken along the x-axis and the dependent variable along the y-axis. For example, in a distance-time graph, t is independent and S is dependent. Therefore, t should be along the x-axis and S along the y-axis.
To represent a physical quantity along any axis, a suitable scale is chosen by considering the minimum and maximum values of the quantity.