I have read kinematics and laws of motion(1st,second and third). In these two chapters one thing i found that firstly distance is taken as first assumption.then it's derivative as velocity OK. then it's(velocity) derivative is taken as acceleration OK. Then it's derivative(acceleration) is not taken!!. but why he(our hero newton) stops at acceleration why not create another quantity named say X which is derivative of acceleration. Is he leave it for vikash(me) to do hahaha LOL!!!!(joke) all derivative are with respect to time. I have an answer for my own question. (1) all motions can be defined on the basis of these three quantities.(mention am i correct here) we all have felt force either due to gravity or due to lifts. when lift moves upward with due to changing velocity we feel extra force. How it feels of having changing acceleration? I mean if a lift is moving upwards with acceleration 2t (t is time). time varying acceleration. then how will it feel.