Ancient Indian thinkers had arrived at an elaborate system of ideas on the motion. Force, the cause of motion, was thought to be of different kinds: 1. force due to continuous pressure (nodan), 2. as the force of the wind on a sailing vessel; impact (abhighat), 3. as when a potter’s rod strikes the wheel; persistent tendency (sanskara), 4. to move in a straight line (vega) or restoration of shape in an elastic body; transmitted force by a string, rod, etc. The notion of (vega) in the Vaisesika theory of motion perhaps comes closest to the concept of inertia. Vega , the tendency to move in a straight line, was thought to be opposed by contact with objects including the atmosphere, a parallel to the ideas of friction and air resistance. It was correctly summarised that the different kinds of motion ( translational, rotational, and vibrational ) of an extended body arise from only the translational motion of its constituent particles . A falling leaf in the wind may have downward motion as a whole ( patan ) and also rotational and vibrational motion ( bhraman, spandan ), but each particle of the leaf at an instant only has a definite (small) displacement . There was a considerable focus in Indian thought on the measurement of motion and units of length and time. It was known that the position of a particle in space can be indicated by distance measured along three axes. Bhaskara ( 1150 A.D .) had introduced the concept of ‘ instantaneous motion’ (tatkaliki gati) , which anticipated the modern notion of instantaneous velocity using Differential Calculus . The difference between a wave and a current (of water) was clearly understood; a current is a motion of particles of water under gravity and fluidity while a wave results from the transmission of vibrations of water particles.