According to Newton's Second Law, consider the case of wanting to accelerate the mass of 3 kg by 3 m/s^2 on a frictionless surface, I need to exert 9 N of force. My question is that
- To let the mass accelerate forever, do I have to exert the force of 9 N forever or just for a short amount of time? What's the difference?
- If I push the same object quickly on the surfacet that has a kinetic friction of 1 N and the object starts accelerating with 3 m/s^2, how will the friction cause the acceleration to change over time?
These kind of things really confuse me. What my teacher teaches is only what will happen immediately after exerting the force but not what will happen after that.