Position path length and displacement
The position of a body in space is denoted by its three coordinates a, b and c. To describe the position of a body, we use a reference point with respect to a set of axes. The set of axes consists of three mutually perpendicular lines labelled as the a, b and c axes. The point of intersection of these three axes is called the origin. To specify the position of a body, it’s a, b and c coordinates are given with respect to this rectangular coordinate system. A stop watch is included to complete the frame of reference.
When any one or more of the coordinates change with time, the body is said to be in motion with respect to the frame of reference. When the coordinates don’t change with time, the body is said to be at rest with respect to the frame of reference. Rest and motion are relative terms, and are always specified with respect to the frame of reference. Positions to the right of P are taken as positive and to the left of P as negative. Positions above P are taken as positive and below P as negative. With time, the position of the body changes and describes a path.
position vector expresses the position of a point P in space in terms of a displacement from an arbitrary reference point P Namely, it indicates both the distance and direction of an imaginary motion along a straight line from the reference position to the actual position of the point.
In considering motions of objects over time the instant velocity of the object is the rate of change of the displacement as a function of time. velocity then is distinct from the instantaneous speed which is the time rate of change of the distance traveled along a specific path. fig.
