 He also concluded that objects retain their velocity in the absence of any impediments to their motion , thereby contradicting the generally accepted Aristotelian hypothesis that a body could only remain in so @-@ called " violent " , " unnatural " , or " forced " motion so long as an agent of change ( the " mover " ) continued to act on it . Philosophical ideas relating to inertia had been proposed by John Philoponus and Jean Buridan . Galileo stated : " Imagine any particle projected along a horizontal plane without friction ; then we know , from what has been more fully explained in the preceding pages , that this particle will move along this same plane with a motion which is uniform and perpetual , provided the plane has no limits " This was incorporated into Newton 's laws of motion ( first law ) . 
