I always thought that $force$ is $mass * acceleration$. Well, that's what I learnt at school a while back. Now, I have been enlightened that force is in fact the rate of change of momentum.
What makes this interesting to me, is that this takes into account a change in mass with respect to time as also playing a role in the force. A nice example of this is that of a rocket taking off. But clearly, this was not an example that Newton had in mind.
So my question: What did Newton have in mind of something where the mass changes with time?
I appreciate that my question is similar to say: How did Newton discover his second law? but I didn't read anywhere there about the concept of change of mass with time.
