Well, at least we got some understanding there, humber. I'm afraid it lost me later. I'm sorry this is so long, and I keep losing my 'y'. I've tried putting them back, but might have missed some. It feels like we might yet solve this boundary layer thing, but I'm not holding my breath!Of course, I see. I never bought into that convention. There are videos and diagrams with things going every which way, so I didn't understand your convention. I guessed right about the method of calculation of the 'rotation'. Excellent.
Amazed. You said 'That is correct'!
Well, as you now understand, the information about which side you were on was not specified, but assumed. Not a convention I joined up to.
You seem to have jumped ahead. This came from you saying 'same from windspeed'. I thought this was the 'real wind' situation, and you were holding the device while travelling forward at windspeed. Not stationary with respect to ground, therefore. And stationary w.r.t. ground does not yield the same as when held moving from cart (real wind), unless the device somehow measures relative velocities with respect to objects it has no direct knowledge of. Moving in the air at windspeed, if it acts like an anemometer, it measures 0, not 10, as I stated.
That makes sense, if 'flow' means boundary layer flow.
Indeed.
Our point rather than yours, I thought.
Missing 'not'? There is not, nor can there be, a difference. Agreed.
Indeed.
I'd have to check what that is. Common sense sais so. Math sais so.
Well we'll just have to agree to disagree then. I urge ou to think about it again, though. If on the cart on treadmill, with the belt moving backwards at 10, the boundari laier seems to be the contentious issue again. Jjcote said that on the ground scenario, the slice of air we were using went slower than the maximum flow, at 6 m/s, instead of 10.
Ok, here's another way to demonstrate my thinking: Wherever those slices of wind are, we agree the relative velocity is the same between them. It's 10 max, 6 at the boundary layer that we're interested in. Difference 4. So, if we are on the cart on a treadmill, at 'windspeed' (even if I let you have that as not a real wind), i.e. 0, then the calculation given above gives the same as I get. 10 - 10 = 0 (i.e. we are keeping up with the wind, ok), so at the boundary layer (BL from now on), it's 6 - 10 = -4. Hence your own formula also gives the BL at -4 relative to us, i.e. backwards at 4 m/s. As I then punched these numbers into the paddle before, we get 0 (top) - -4 (lower) = 4 m/s "CW".
Sure it does. But 'moves with the belt' is a biased viewpoint. When the wind blows over the land, the 'flow moves with the land' - we don't normalli express it that wai, we sai it is slowed down bi the land instead, BUT THESE ARE JUST DESCRIPTIONS DEPENDENT ON OUR FRAME OF REFERENCE! If it seems right that the land slows down the wind, not the 'flow' moves with the land, just remember the earth spinning scenario. The air can be motionless w.r.t. the earth, and the land moving under it. We experience that as REAL WIND, and it is SLOWED at the BL.
This is for going with the belt? So I agree we have 10 m/s on our backs, 6 m/s on our knees or wherever. This is exactli what we had when standing on the ground in 'real wind'. How come that was CW, and this is CCW? Wind and 'flow' are going left to right w.r.t us. If we face forward, they're still on our backs as they were on the ground. Stand to right of cart in 'real wind' as it races past. Someone standing on the ground, facing the way the cart goes, has wind on back - well, we already did that one. Please, how did you still manage to reverse the sense of that to CCW? In the face of all comers. All of physics would agree with me. Each person, with their eyes closed, can't tell the difference. Suddenly we're supposed to have the paddle going the other way because we've put the thing on a treadmill. Amazed.
Oh crap, this looks like it's when moving with belt. That would make your numbers for the above even worse, if they were for the cart perspective. Oh well. Apply earlier argument here instead! Look, I agree with the 10 from rear, but you can NOT HAVE THE LOWER AS 6 m/s from the FRONT!
Is this actually it? Is this your contention? That if we blow air over a surface, it has a gradient from positive max to positive minimum, but if we move a surface past a mass of air, its flow is reversed at some point down the gradient? That is what you have described, 10 from rear at the top (because we're ploughing into it with our backs), 6 from
front lower down?! What physical effect could possibly cause the wind near the ground (sorry, belt) to reverse direction? No, our knees are also ploughing into the stationary air in the room, except it's not
quite stationary. It is moved backwards, as you agree, by the belt (Backwards, that is
w.r.t. the room). Hence, our knees plough into it while it is
not quite stationary, and feel a 6 m/s worth of cooling effect, a flow from the rear. How pleasant (until we fall off onto the carpet). How can we possibly be moved backwards by standing on a belt, fall off the back, and report that while we did that, our knees had a wind on them from the front? Please try to understand this point: yes, from the room's perspective, the boundary layer is dragged with the belt. From our perspective when standing on the belt going backwards, we are still ploughing through it backwards. The belt doesn't speed it up to belt speed at that height (I'm calling knee height). It speeds it up to belt speed right at the belt level, so the soles of our shoes feel no wind. Everywhere above that, we feel a wind on our backs. I FEEL UTTERLY SURE THAT NO-ONE CAN POSSIBLY READ THAT, WITH A LITTLE PATIENCE AND CONCENTRATION, AND NOT SEE IT. IF I'M WRONG, PLEASE TELL ME HOW YOU CAN BE WHIZZED OFF A TREADMILL BACKWARDS AND FEEL THE WIND ON YOUR FRONT AT ANY HEIGHT. SERIOUSLY. LET'S HAVE THIS ENDED FOR CHRIST'S SAKE.
I'll remind you that this is the normal physics drawing board. Yours is the screwy one. Tri again. Iou'll get it eventualli.
Stationary and windspeed? Stationary w.r.t. the room? That
is windspeed. You really would make a lot more progress if you remember every time you express a velocity, it needs a w.r.t. something (stated, or clearly implied). "Stationary" means nothing.
Sorry, I still don't understand this point at all, but it seems wrong if it means accelerating to what we would consider faster than windspeed, and continuing beyond - like if there were miles of treadmill ahead. As we go faster, the difference between the wind max and the boundary layer remains the same. How can it get to zero, so as to stop the paddle rotation, without it actually changing its gradient? There is still belt having an effect on the air, and air at a greater remove that isn't being affected, even if you don't agree what the gradient is. If that were true, why wouldn't the real wind gradient change as we drove faster? Maybe I misunderstood what you're saying there.
anyway, I've got nothing to lose from a bit of practice.
