in this sketch suppose the velocity of ball is 0 and it is out from the system and stayed in 0 velocity due to two electromagnets and these two magnets are attached with two springs and both springs are in stretched position towards up and down side . The ball is expelled from the gun system and got 0 velocity after expelling from the system by using these electromagnets and a force is also applying on these magnets and springs are in stretched position. you will say that engine will not move as net force is ZERO but if we release these spring then what will be happened with engine as after releasing these springs both will work to propel the engine ? should it move or not or can we modify the direction of this engine ? please keep aside the issue of ball retrieving. Thanks
When you fire the ball, you use the gun to put a force on it, pushing it backwards. Newton's Third Law tells us that "for every action, there is an equal and opposite reaction". This means that the gun will experience a force pushing it forward.
If you want to stop the ball, you must apply a force to it. However, in doing so, you will also apply a force to whatever is stopping the ball. In this case, it would be the electromagnets attached to the springs. This will cause the springs to stretch out. However, this will put a force on the gun, since the springs are attached to the gun. This will pull the gun back to its original position and stop it, resulting in no net motion and no net velocity.
You cannot create an engine that does not expend fuel or energy to move. The Laws of Thermodynamics state that in order to do any kind of work, such as moving something, we will lose energy. If you think you have found a way to propel a spacecraft without ever losing propellant, you haven't. No matter what you think, it cannot be done.