POSITION PATH LENGTH DISPLACEMENT PHYSICS III MOTION IN PLANE
If one or more coordinates of an object change with time, the object is in motion. Otherwise, the object is said to be at rest. For describing motion in one dimension, we need only one axis. To describe motion in two/three dimensions, we need a set of two three axes.
Consider the motion of a car along a straight line. To describe motion along a straight line, we can choose an axis, say X-axis. We then measure the position of the object with reference to a conveniently chosen origin, say O, as shown in Fig. 3.1. Positions to the right of O are taken as positive and to the left of O, as negative. Following this convention, the position coordinates of point P and Q in Fig. 3.1 are +360 m and +240 m. Similarly, the position coordinate of point R is -120 m.
x axis origin and position of car at different times
Motion of an object can be represented by a position-time graph. For motion along a straight line, say X-axis, only x-coordinate varies with time and we have an x-t graph.
E.g. a car standing still at x = 40 m (stationary body). The position-time graph is a straight line parallel to the time axis, as shown
Uses of position - time graph 1) To determine the position at any
instant 2) To calculate the velocity [from the
slope of the graph)
3) To calculate the displacement (x2 - x1) during any time interval [t2- t1]
