1. The problem statement, all variables and given/known data Is it possible for a particle to describe a curved path if no force acts on it? Is the answer reference frame dependent? [I am sorry. I forgot that the rule says on question per thread. ] 3. The attempt at a solution YES, when the body stays still but the frame describes a curved path. Then with respect to that frame the body will describe curves but no force would act on particle. Will we count pseudo force as a force?