The description of motion of a body involves its position at any instant, its displacement, average velocity, instantaneous velocity or velocity, average acceleration and instantaneous acceleration or acceleration.
Consider a body moving in the x-y plane represented by the rectangular coordinate system.
At an instant in time t, it is at point P, which has (x, y) as its coordinates.
This displacement vector Δr
is directed from P to Q. In component form the position vector is r
) – (xi
The average velocity of a body is the ratio of displacement and the corresponding time interval. The direction of velocity at any point on the path is tangential to the path at that point and in the same direction as that of motion.
The instantaneous acceleration or acceleration is limiting values of the average acceleration as Dt approaches zero. We can understand this limiting process by using graphs describing the motion of the body.