Question

It is sometimes heard that inertial frame of reference is only an ideal concept and no such inertial frame actually exist . Comment

Answer 1

It is rightly said because if we think earth is rotating along its axis and revolving around sun also, so earth cannot be an inertial frame, similarly sun is revolving around our galaxy, galaxy also moving in universe, actually we cannot name a single thing in universe to have absolute rest or absolute motion state so this concept does not actually exists but for practical applicability we can think earth to be inertial frame and solve problems.This was give by einstein mainly.