I am confused about changes in gravitational potential energy, net external force, and work-energy theorem.
For a single particle system, I understand that a net external force results in a change in kinetic energy and thus work is done on the system (particle).
What I am confused about is the work done on a system and the increase in gravitational potential energy.
If I define the system to include a book + Earth, (where I am external to the system) and I lift the book at a constant speed, then the net force on the system is not zero - correct? However, the net force on the book is zero. So, by Newton's Second Law, the system should accelerate and there should be a change in kinetic energy and thus work will be done on the system.
However, most books state that there is no change in kinetic energy but a change in potential energy instead. How can I apply an external force to the system increasing the energy of the system but the system not accelerate? If the amount of kinetic energy remains constant then is work done on the system?