This is a very basic question about the concepts of force and acceleration. Consider the following situations:
- I sit on the floor of my room on earth
- I sit on the floor of a spaceship that accelerates with 1g (in a direction perpendicular to its "floor")
In both situations I feel the same (a force that presses me towards the floor). Both situations involve an acceleration of 1g. BUT: in situation (2) my velocity changes, while in (1) it does not.
My question: what is the essential difference between these situations?