For an observer standing still on the belt (in other words, at rest in a frame of reference that is moving at the same velocity as the belt), the car is observed to be moving in both cases.
Observation has got
nothing to do with this problem, Clive, but it is certainly the cause of it. Objects do what they do, even if there is nobody watching. The car will not experience acceleration, so it will not be displaced, so there is no motion. That is that. Observer stuff is not appropriate.
We know that the Earth goes around the Sun, because the acceleration is indicative of a much smaller mass than the Sun. So the Earth must be orbiting the Sun, and not the other way around.
Similarly, the car and observer can be separated by the same means. The rate of acceleration will tell which is moving and which is not. If you take the car as a mass and put it on the belt, so it goes with the belt, you can monitor its acceleration. Do the same for an observer. That information can be used to identify which of the two objects is moving. For all the purposes of this forum, and the Newtonian world, acceleration is an absolute.
There is no way that the observer can get on the belt and to speed, yet not experience acceleration. Declaring "steady state" will not do, nor is it needed.
Depending on the actual direction of the belt movement and your position and orientation on it, you may see the car moving directly towards you and finally impacting your shins in a very painful fashion. If the air is not moving relative to the car body while this is going on, then you will also feel a it headwind.
Yes.
In other words, from a frame of reference that is moving with the belt, the car is seen to be moving (and so also your house and the road and trees beside it and so on). We have put ourselves into a different frame of reference, where positions of things are now measured relative to some origin that is moving at the same velocity as the belt.
Yes, but it is
you not the car that is moving. 100% guaranteed identification. When I said this much, much, earlier, out came Einstein and the hobo or similar. No connection whatsoever. I can measure and identify which is moving on the belt or w.r.t the ground or both. No problem at all.
The origin of our x-y-z coordinate system could be co-located with an X marked on the belt between our feet for example. Velocities of all objects in this reference frame are determine from the rate of change of their position with time (position measured in the same reference frame). Acceleration is the rate of change of velocity with time.
Yes.
Of course, you can also use a frame of reference that is at rest with respect to the road the car is parked on if you wish. For an observer at rest in that reference frame, the car appears to be at rest. Thus the car can be said to be moving in one reference frame, but at rest in another. The actual values of its position and velocity (and thus also kinetic energy) in each of those different frames of reference will also generally be different. Yet the results of predictions based using on Newtonian mechanics will be the same. The forces will be the same. Mass hasn't changed. Time hasn't changed. And acceleration doesn't change. Try it!
The question is if it is possible to tell if the observer on the belt is moving.
or the cart is moving. Yes. No problem. If both are at a constant velocity, then that is no a problem either, because one will be moving so there will be displacement. But again, so what?
Real World.
If I put a car on the road and drive it, an accelerometer will tell me that I have been accelerated, while a ruler will tell me I have been displaced.
Cast iron, 100%
Treadmill
Put that same car on a working treadmill, and I will get zero in each case.
Cast iron 100%. (This is because a vehicle powered by the belt cannot move with the belt in a meaningful way, it may move a bit dependent on belt friction)
The important bit
Displacement w.r.t the belt is
not important at all.
The reason is that the belt, in windtunnels, is a
model of the road
surface, and not anything else. Thid idea has been taken to make road, but that is wrong.
The belt is artificially derived, from
assumed travel, but the cart is
real.
That is the real test object, and there is no doubt that gravity will tell you that it is real, so it's datum is ground.
The datum is the ground not the belt.The value of the belt is easy to assess. Add another one at 90 degrees, one on the roof, a pink one underneath the black one, one under the seat. One on the front wheels going South, another on the left side, going North. No real connection to travel at all. It's a belt.
One of them, if correctly built and placed, may give you a simulation of the boundary layer.
The BMW/F1 is the same. The datum is the ground, and in the wind tunnel, the cars velocity is zero, which is why it does not leave the building.
That's it. The belt is not a road, but the
real ground is. The belt is an entirely artificial construct, that has nothing to do with motion of the vehicle. It
may spin the wheels, but will simulate the road surface even the wheels are not on the same belt, or even turning.
There is
no doubt that the the real ground, is the ground that you stand on, when next to the treadmill. That is what you see.
Windspeed, is a figment. All the odd effects that you see, -KE, no KE, and so forth, are the result of trying to support that notion.
If I have not convinced anyone that he cart is a balance, then it is quite easy to show that a car or any wheeled vehicle driven by the belt, cannot have any useful motion.