Suppose there's a rocket in space with a mas m, and an object also with mass m. Now suppose the rocket turns on and pushes the object with a constant force F. The object would then have an acceleration a. By Newton's Third Law the object pushes back with a force -F. So shouldn't the rocket have a negative acceleration (-a) and thus eventually slow to a stop? But what happens in reality is the rocket pushes the object faster and faster. I must be missing something fundamental here. Set me straight so I can stop thinking about this friggin' thing in the shower. Thanks.