  The motion of rockets is part of the study devoted to the motion of variable
mass systems. Notably those in which the mass leaves permanently the considered
system. Rockets are propelled forward by the reaction force produced by the hot
exhausted gases ejected from their tales in the rearward direction. Thus their
motion should not violate Newton's third principle of the equality of action
and reaction forces during the exhaustion process. Nor should it violate
Newton's second law of motion judged by inertial observers. However a close
examination of the study of the motion of rockets in a major part of physics
textbooks, if not all reveals erroneous determination of the expression of the
thrust force that pushes the rocket in the forward direction. The false
expression of the thrust force entails a bad effect on obtaining the right
differential equation that governs the motion of rockets. This trap induced
some prominent physics authors to pretend the in applicability of Newton's
second law in such particular cases. Not only that, but they also modified
Newton's second law in order to fit their purposes of obtaining the right
differential equation, historically known under the name Tsiolkovsky rocket
equation. The object of this paper is to give the true expression of the thrust
force and to write the differential equation of motion of rockets without any
necessity of modification of the classical laws. The paper also delves into the
expression of the change of velocity of rockets, and proves that their motion
is uniformly accelerated in the early stages of liftoff from the ground at
condition of constant velocity of expulsion of hot gases from their nozzles.
