I'm trying to understand an example on page 107 of "Fundamentals of Fluid Mechanics" seventh edition by Munson, Okiishi, Huebsch, and Rothmayer. The setup of the question is:
Consider a flow of air around a bicyclist moving through still air with velocity $V_0$
In the solution, there is a statement that says that in a coordinate system fixed to the ground, the flow is unsteady as the bicyclist rides by. The Bernoulli equation requires that the flow be steady if it is to be used properly. But in a coordinate system fixed to the bike, it appears as though the air is flowing steadying toward the bike with speed $V_0$. This is the proper reference frame to use.
Question 1: Why does the coordinate system fixed to the ground see an unsteady flow? Maybe I don't understand what steady flow is. From my knowledge, steady flow is where any snapshot of the flow does not change with time. This doesn't mean that the streamlines must be straight, only that each successive particle that passes a given point will follow the same path (i.e., if you are on one streamline, you stay on it and don't divert off of it). Also, does steady flow require that the velocity be constant on each streamline?