Originally Posted by tom28571
The source on the road is the wind and the source is the treadmill in the other case. Seems like an important distinction to me.
The reason the vehicle can advance along the treadmill is because the propeller is being driven by the wheels and the propeller is moving air backwards to generate thrust. It is the air thrust that keeps the vehicle advancing along the treadmill. The same propeller thrust moves the vehicle against a tail wind on a roadway.
The reason you see a distinction is that you are still acting as an external observer and concerning yourself with the ultimate source of energy. I agree that there is a difference here but it is immaterial to what the vehicle sees. You have to place yourself on the vehicle to see it from the vehicle perspective. Consider yourself sitting on the vehicle placed on a huge treadmill with trees and all stuck to the treadmill. You will see your visual world passing by and a slight head wind as the propeller drives you along against a tail wind.
Now take the vehicle out on the roadway where there is a tail wind and get it moving at a speed just so there is a slight headwind. You will experience exactly the same things as you did on the massive treadmill. Your visual world will be moving past you and you will experience a slight headwind.
In fact the earth is already moving at a hell of a rate it is just that you cannot stand far enough back to see it unless on a space ship. Just happens the air is moving roughly at the same speed at the earth. What is the ultimate source of the wind energy anyhow? How far back do you want to stand? For this situation you need to plant yourself on the vehicle and look around. Whether on a treadmill in still air or on a roadway with a tail wind your world is the same.
If you are bogged down understanding this then it might help if you work through my 4 slides.