Merged DDWFTTW in a “Real” Wind

[windgrins]

Humber illustrates a Great aerodynamic point by example.

Humber,

I just can't bring my self to modify my post above as I'm still giggling about my reply. (Immodest, I know, but I think its funny!)

You actually just proved the point very well. You've stated in the past a lot about accuracy of measurements and I agree that all the windtunnels I have been to (only 3), they have been sticklers for accuracy of the wind speed in their tunnels as that is sort of the point of the whole thing.

When the wind tunnel speed control reads "100 m/s", that means that the model which is attached to ground, has a relative wind on it of 100 m/s.

and from the following table:

Speed Control.................. Relative wind on model

90 m/s............................90 m/s
50 m/s............................50 m/s
30 m/s............................30 m/s
20 m/s............................20 m/s
10 m/s............................10 m/s
0 m/s..............................0 m/s (windspeed)

So if one wants to study an object at windspeed, they would turn the windtunnel to 0 m/s=still air.

I'm assuming you think this is totally wrong. Surprise me!

Regards,

WindGrins

 

[windgrins]

Answer to your Humber's question

Humber,

Sorry, I did forget to answer your question concisely.

Spork is still welcome to answer as a sees fit.

As for me, I would rather he use his time responding to posts that I don't understand and that I think he can shed some light on.

Spork answering this question for me is like answering the question "does a 2 lb brick have mass?

I'm comfortable in my personal knowledge. Harold or Yev may want to see Spork answer this, however.

Regards,

WindGrins

 

[mender]

I would politely ask also that other posters feel free to comment on my argument from above. I'm OK with feedback here and there may be something I'm missing.

It may be prudent to clarify that "at windspeed" includes traveling in the same direction as the wind.

 

[Llyricist]

Or just say "at the average velocity of the air that encompasses it".

ETA: Yes, I know that just opens up humber's other can of worms.

 

[mender]

What about a big and massive balloon? It is traveling downwind at windspeed. A bird moves towards it at 1mph relative to the balloon. If a WS balloon can be said to be like a balloon in a room, then coaxing the bird towards the balloon should be the same thing.
Galilean Relativity does not allow velocity to be arbitrarily dispensed with.

It's things like this ...

 

[humber]

Humber,

I just can't bring my self to modify my post above as I'm still giggling about my reply. (Immodest, I know, but I think its funny!)

You actually just proved the point very well. You've stated in the past a lot about accuracy of measurements and I agree that all the windtunnels I have been at (only 3) have been sticklers for accuracy of the wind speed in their tunnels as that is sort of the point of the whole thing.

When the wind tunnel speed control reads "100 m/s", that means that the model which is attached to ground, has a relative wind on it of 100 m/s.

and from the following table:

Speed Control.................. Relative wind on model

90 m/s............................90 m/s
50 m/s............................50 m/s
30 m/s............................30 m/s
20 m/s............................20 m/s
10 m/s............................10 m/s
0 m/s..............................0 m/s (windspeed)

So if one wants to study an object at windspeed, they would turn the windtunnel to 0 m/s=still air.

I'm assuming you think this is totally wrong. Surprise me!

Regards,

WindGrins

So, a bird traveling at 1mph relative to the plane, but the other way.
Can then be simulated by turning the fan off, and throwing the bird at the nose of the plane at 1mph? Or is there a difference between closing speed and relative speed? Won't the total KE be different in the air, than when the fan is off, even if they were traveling the same way?

I perform the following experiment. With a table, table cloth and some dinnerware. Using a strain gauge to measure the force as I pull the cloth at speed x, I note a moderate force of 20N. That is due to the force of friction between the table cloth and the table. Using the same strain gauge, I tether the tablecloth to the wall, and pull the table at speed x. The strain gauge still reads 20N, but now there is a static force of 20N in the wall.
I also note that I am doing a lot more work, and that there is noise that was not there before. There's more to motion than velocity. The TM is a triple joke.

 

[humber]

It's things like this ...

Would you like to see Spork shoot me down in a challenge about fluid dynamics?

And your views of relative motion are silly.

 

[CORed]

Wait: Is this it, from way back on page 59?




Seriously though, is that it? I can kinda see your hands waving, and Newton spinning in his grave, but I can't see anything approaching a cogent argument for a balloon, released at above windspeed, slowing to below windspeed.

Can anyone else see it hidden in there?

The balloon can never get to the state where (Vwind - VBalloon)^2

Either that "^2" doesn't actually mean "to the power of two" or part of humber's formula is missing. Assuming that is does actually mean "to the power of two, there's obviously an "=" or an inequality missing. I think he just did some random copying and pasting of sciency stuff and didn't notice that nothing there makes any sense.

In short, there doesn't appear to be anything there remotely resembling a proof of anything.

 

[humber]

It may be prudent to clarify that "at windspeed" includes traveling in the same direction as the wind.

It may be amusing to note that you were only delivered of half the idea you paid for.

 

[windgrins]

Mender, I think I see your point.

It may be prudent to clarify that "at windspeed" includes traveling in the same direction as the wind.

Mender,

Oh, I see now--you mean I should have stated-

that this demonstrates that a balloon in a steady state wind will move at the speed of the wind-traveling in the same direction as the wind.

OK!

I thought it obvious but that has led us to trouble before.

Thanks,


Regards,

WindGrins

 

[mender]

The strain gauge still reads 20N, bur now there is a static force of 20N in the wall.

Which was on the floor when you were pulling the cloth; now the wall is doing what you were doing, so that's where the 20N force is.

I also note that I am doing a lot more work, and that there is noise that was not there before. There's more to motion than velocity.

Not according to the cloth and the strain gauge attached to it. But that would require you to understand FORs, and that's apparently off-limits in this discussion.

 

[mender]

Would you like to see Spork shoot me down in a challenge about fluid dynamics?

And your views of relative motion are silly.

Maybe after you get through with the present discussion; we'll see how you do.

Thank you.

Now back to our regularly scheduled program.

 

[humber]

Which was on the floor when you were pulling the cloth; now the wall is doing what you were doing, so that's where the 20N force is.

Static force does no work. The floor supporting you does no work but provides an opposing force to that of gravity. Work = force*distance.
There is still a force that was not there before.

Not according to the cloth and the strain gauge attached to it. But that would require you to understand FORs, and that's apparently off-limits in this discussion.

The energy to pull the table must come from somewhere. In the initial case, I way find I do little work, but in the other, a lot.
Looks like relative KE only works one way. That may say a lot about a prop trying to beat the headwind.

 

[mender]

I thought it obvious ...

It is, therefore humber will take it to mean the opposite.

 

[humber]

Maybe after you get through with the present discussion; we'll see how you do.

Thank you.

Now back to our regularly scheduled program.

When you are rattled, you post short whimsies.

 

[mender]

Static force does no work. The floor supporting you does no work but provides an opposing force to that of gravity. Work = force*distance.
There is still a force that was not there before.

It's things like this...

 

[windgrins]

Ask someone who has had a physics course

So, a bird traveling at 1mph relative to the plane, but the other way.
Can then be simulated by turning the fan off, and throwing the bird at the nose of the plane at 1mph? Or is there a difference between closing speed and relative speed? Won't the total KE be different in the air, than when the fan is off, even if they were traveling the same way?

I perform the following experiment. With a table, table cloth and some dinnerware. Using a strain gauge to measure the force as I pull the cloth at speed x, I note a moderate force of 20N. That is due to the force of friction between the table cloth and the table. Using the same strain gauge, I tether the tablecloth to the wall, and pull the table at speed x. The strain gauge still reads 20N, but now there is a static force of 20N in the wall.
I also note that I am doing a lot more work, and that there is noise that was not there before. There's more to motion than velocity. The TM is a triple joke.

Humber,

In all seriousness, I suggest you ask someone about my previous two posts who has had or teaches a high school senior or first level college physics course. No need to report back to us. Just do it for your own benefit. There are plenty of other forums on the internet where you can get this kind of question answered from a neutral party. Just quote the actual text and present it for an answer. Again, no need to report back to us.

ETA: PS, If you feel the need to report an answer back to us that you get off the internet, just include the link where you asked the question and where they gave you an answer.

Regards and signing off for the evening.

WindGrins

 

[ThinAirDesigns]

When you are rattled, you post short whimsies.

When you are rattled, you post.

JB

 

[mender]

When you are rattled, you post short whimsies.

Really? Good to know, thanks!

 

[windgrins]

So, a bird traveling at 1mph relative to the plane, but the other way.
Can then be simulated by turning the fan off, and throwing the bird at the nose of the plane at 1mph? Or is there a difference between closing speed and relative speed? Won't the total KE be different in the air, than when the fan is off, even if they were traveling the same way?

I perform the following experiment. With a table, table cloth and some dinnerware. Using a strain gauge to measure the force as I pull the cloth at speed x, I note a moderate force of 20N. That is due to the force of friction between the table cloth and the table. Using the same strain gauge, I tether the tablecloth to the wall, and pull the table at speed x. The strain gauge still reads 20N, but now there is a static force of 20N in the wall.
I also note that I am doing a lot more work, and that there is noise that was not there before. There's more to motion than velocity. The TM is a triple joke.

There is no difference between closing speed and relative speed. They are the same concept. Make a well formed question about a bird and I'll attempt to answer it.

According to your description, In the first case you are pulling the tablecloth off the table. In the second case you are pulling the table cloth across the table and the table across the floor. There is additional friction in the feet of the table so the gauge will read the friction due to the tablecloth plus the friction due to the table legs on the floor if you are pulling the table with the gauge and it will read more than 20N. If the gauge is between the tablecloth and the wall, it will read 20N. That additional noise you hear is the feet of the table sliding across the floor and your grunts to pull it.

Sorry two different situations.

PS, You have used up the last of the trivia questions with me. If you have an interesting question, I'll try to answer it.

Regards,

WindGrins