If the time interval D
t is sufficiently large then the velocity obtained is called average
velocity. For as accurate description of motion it is necessary
to choose D t as small as possible
i.e. D t ®
0; then the velocity obtained is called instantaneous velocity.
As the displacements must be directly proportional
to the interval of time hence the ratio of displacement to time
interval will
be constant whether Dt is sufficiently
small or arbitrarily large.
Similar considerations also apply to acceleration also
Even if acceleration keeps on changing with time,
we do not find it necessary to consider the rate of change in acceleration
for the description of motion, and so on. The reason for this will
be found when we study dynamics. The causes of acceleration are
forces according to Newton's laws of motion.
