Split Thread The validity of classical physics (split from: DWFTTW)

[humber]

Back to the kites for a moment: to help clarify whether there is an actual difference in the two scenarios that you proposed, let's extend the length of the kite string, raise the height of the kites as they are flying, and add a cloud layer between the kites and the ground. To observe and record the behavior of the kites, a helicopter with a camera crew is hovering nearby.

No, let's not. However, today is "be conciliatory day", in my native village

The first kite is launched into a 10 m/s wind and the holder of the string is standing on the ground and not moving. The kite goes up over the clouds. When the camera crew reports that they are in position and filming, the kite string is severed right next to the kite and the result is filmed.

The second kite is launched on a day with no wind and the holder of the string is standing on a very long treadmill moving at 10 m/s (or the holder is standing in the back of a truck that is driving along a road at 10 m/s, your choice). The kite goes up over the clouds. When the camera crew reports that they are in position and filming, the kite string is severed right next to the kite and the result is filmed.

Would there be any way that the film crew and/or anyone watching the videos afterward could tell the difference between the first kite and the second kite by what happened after the string was severed?

Yes. Countless ways.

Bonus question: before the kite string is severed, what is the air speed of the helicopter if it stays exactly in position wrt the kite in scenario#1 and in scenario #2? The same in both cases, different, or opposite?

There are no helicopters in my drawings.

That's pretty close: at best, it will model what the cart does outside in a perfect wind. Fortunately, modeling what the cart does outside in a perfect wind (no gusts or direction changes) allows a much more precise way of comparing the cart's speed to the speed of the wind to determine if/when the cart matches the speed of the wind (which it sees as still air at that point). In both cases (outside case and treadmill case), the KE change in the air surrounding the cart is the same.

That's how the cart is powered, by the change in KE of the air surrounding the cart. If you have been playing the many-leveled game that RP thinks you are, you should be able to say, "Well done, mender, my work here is finished". If you still insist that the cart would have to be magic to achieve DDWFTTW, well, I'm not sure that anything anyone can say will ever change your mind.

What say you, humber?

Null point. Way too many new variables and unnecessary complication. Keep it simple.

On the Treadmill.
Anubis drags the kite through the air by the string, otherwise there is no air motion over the kite at all.
Upon release, the kite will still be carried forward, but powered by the KE stored in its mass. During this time, the kite (or any other wind borne object) will decelerate, meaning that its average velocity is less than that of the belt during that period, finally terminating at zero (w.r.t the ground or windspeed w.r.t the belt) when all available KE is dissipated.
During this same period, Anubis has moved further to the left while the balloon is decelerating, lending the impression that the balloon is moving away from him, though it is still actually moving towards him.
This must be true, as the balloon's average velocity is less than that of the belt, yet not zero, or in the opposite direction.
When all KE is exhausted, the kite will fall to the belt, and remain a fixed distance from Anubis.
(1) Upon release, the treadmill (windspeed) observer sees the balloon move a little the left, then quickly drop.
(2) A ground observer sees the same.
(3) Belt observer sees the balloon still coming towards him, but slower, then drop.
Conclusion: Ground and windspeed observers are the same. The cart is motionless for both observers. A quorum that says it is not moving.

In Wind
If a stable kite is released in wind, it will be carried away for as long as the wind may drive it. It can fly away to be out of sight. Hence "lost kites".

The motion as the kite is released, is not apparent, but real and time continuous, and the same for all observers. Also, there is no motion towards the kite handler upon release.
As I have said, the only time the treadmill is even close to a model of the real wind, is if and only if, the object is fixed to the belt.
The cart is never seen to do this of course, but could not make progress up the belt if released. ( If the cart can spin-up to get to balance, then it may reach that state before becoming unstable, but that is not real progress up the belt)

The quotable humber:
If actually moving with the belt, (motion w.r.t the ground) the cart cannot move w.r.t the belt, so as to be seen making real displacement along that belt. That is impossible for any vehicle without energy storage, that is driven by the wheels.

So, Mender, what do you say?

ETA:
You Tube video delayed due to time, but definitely in production.

 

[humber]

No, he didn't do any of those. He asked you to "suppose...xyz" and say how you would respond. It is your lack of logic and imagination that is being demonstrated, along with the reluctance to consider this as a possibility.

We know the real answer: you'd tell them they were wrong, with some waffle ending "QED", and tsk tsk at them for being so stupid.

I say that he did. And you just added at least another 3 to the list, John.
(8) Presuming the outcome.
(9) Appeals to personal authority
(9) A True Scotsman in "real" answer
http://en.wikipedia.org/wiki/No_true_Scotsman

You also fail to differentiate between possibility and probability.
A though process common to conspiracy theorists and creationists, but for opposite reasons.

ETA:

He might even end up teaching a bunch of students it, musing about how counterintuitive it is and how ordinary people tend to believe in absolute motion and kinetic energy

Ooops.

 

[humber]

They didn't let the lab rats fly the planes,

They should. For one thing, rats they are less obsessed with buttons;
either on a uniform or in the cockpit.
That not withstanding, rats are brilliant information processors. Constantly learning and adapting to change, while maintaining a balance between risk and reward. Superb animals. I think I would feel safer with a rat as pilot.

(especially low level lab rats, since I was a lot younger back then) so I never got to actually feel how it handles. Nice to hear from another happy customer though.
I always preferred a simple, direct mechanical connection to my control surfaces anyway. And if it can hover, all the better.

 

[humber]

No you don't.

No you haven't.

I do actually. Raced a few month ago. Lap time 2 minutes. Hurrah for humber! Well no. The lap record is 1:18.
Taking a one second off two minutes, is brown underpants time, yet someone can take off 42 seconds. Unbelievable.

So, I just don't care what you believe, Spork

 

[John Freestone]

I say that he did. And you just added at least another 3 to the list, John.
(8) Presuming the outcome.
(9) Appeals to personal authority
(9) A True Scotsman in "real" answer
http://en.wikipedia.org/wiki/No_true_Scotsman

You also fail to differentiate between possibility and probability.
A though process common to conspiracy theorists and creationists, but for opposite reasons.

ETA:

Ooops.

No. Once again, it is you who has failed to differentiate between a hypothetical, a conditional (if....) and a statement of belief or fact, and assumes that the logic pertaining to it has been assumed to be true by the one posing it. In fact, I was about to add that I do not like or agree generally with argument that is based on appeals to authority, or the number of people who believe something, and you fail to understand that I can dislike that as a line of argument, yet also pose it (not that I did) as a thought experiment.

Your argument above is the same kind as if I had said, "Humber, if a doctor gave you the diagnosis of a narcisistic personality disorder, would you believe him?" and you had listed all the stupid assumptions I had made about personality disorders, the authority I invest in doctors, etc., etc.

It seems that your imagination, the ability to think things that may or may not be true, is as limited in the social realm as it is in the scientific.

 

[Michael C]

Kites can fly without string. A simple fact.

A simple fact? No, more like a miracle. Could you show us a kite that can fly without string?

 

[fredriks]

Humber, cant you see the problem in your writing?
Did you mean kite when you wrote balloon? I assume you did.

Anubis has moved further to the left while the balloon is decelerating, lending the impression that the balloon is moving away from him

Yes, correct.

though it is still actually moving towards him.

How is it possibly to draw this conclusion? Did Anabis leave the belt or what?

This must be true, as the balloon's average velocity is less than that of the belt, yet not zero, or in the opposite direction.

What you say are true but your conclusion above is definitely wrong. Anabis moves faster relative to the air than the kite but in the same direction. The distance between them is thus getting larger

(1) Upon release, the treadmill (windspeed) observer sees the balloon move a little the left, then quickly drop.

Left relative to what? Not the observer at least.

The rest is the same nonsense.

Humber, here is a serious comment.

An observer on a belt and on the ground besides the belt can see the same thing relative to something they have in common and calculate the same velocities relative to something they have in common. This is not was this is about.

This is what the observer sees relative to them self.

Anabis flying his kite in a breeze is going to see the exact same thing as when he fly his kite from a belt if he compare everything relative to him.

 

[fredriks]

double post

 

[John Freestone]

On the Treadmill.
Anubis drags the kite through the air by the string, otherwise there is no air motion over the kite at all.
Upon release, the kite will still be carried forward, but powered by the KE stored in its mass. During this time, the kite (or any other wind borne object) will decelerate, meaning that its average velocity is less than that of the belt during that period, finally terminating at zero (w.r.t the ground or windspeed w.r.t the belt) when all available KE is dissipated.
During this same period, Anubis has moved further to the left while the balloon is decelerating, lending the impression that the balloon is moving away from him, though it is still actually moving towards him.
This must be true, as the balloon's average velocity is less than that of the belt, yet not zero, or in the opposite direction.
When all KE is exhausted, the kite will fall to the belt, and remain a fixed distance from Anubis.
(1) Upon release, the treadmill (windspeed) observer sees the balloon move a little the left, then quickly drop.
(2) A ground observer sees the same.
(3) Belt observer sees the balloon still coming towards him, but slower, then drop.
Conclusion: Ground and windspeed observers are the same. The cart is motionless for both observers. A quorum that says it is not moving.

In Wind
If a stable kite is released in wind, it will be carried away for as long as the wind may drive it. It can fly away to be out of sight. Hence "lost kites".

The motion as the kite is released, is not apparent, but real and time continuous, and the same for all observers. Also, there is no motion towards the kite handler upon release.
As I have said, the only time the treadmill is even close to a model of the real wind, is if and only if, the object is fixed to the belt.
The cart is never seen to do this of course, but could not make progress up the belt if released. ( If the cart can spin-up to get to balance, then it may reach that state before becoming unstable, but that is not real progress up the belt)

The quotable humber:
If actually moving with the belt, (motion w.r.t the ground) the cart cannot move w.r.t the belt, so as to be seen making real displacement along that belt. That is impossible for any vehicle without energy storage, that is driven by the wheels.

So, Mender, what do you say?

ETA:
You Tube video delayed due to time, but definitely in production.

Did Anubis get his kite from Walmart, too? It keeps randomly turning into a balloon.

You're quite right (-ish) that the liberated kite only gives the impression of moving away from Anubis, when in fact it is "moving towards him"...as long as you include in this odd terminology the fact that he is moving away from it faster than it is moving towards him. Ever noticed what happens when you go away from something that's coming towards you slower?

Your arguments go like this: I'm on a bus, watching a person on a pushbike out the back window as he peddles "towards me". The bus is going faster than him. He's still going "towards me". I can tell that because he's peddling forward, not backward (that is impossible on his sort of bike, and would be a very silly thing to do!). So obviously he is moving towards me. QED. After a day's travel, and while we're both still going at our steady velocities, he'll still be "coming towards me". Oddly, I won't be able to see him anymore, because he's so far away, but he's still "coming towards me" (I insist)!

 

[John Freestone]

ETA:
You Tube video delayed due to time, but definitely in production.

Delays are always caused by time.
"Definitely in production" means you remembered to think about the subject long enough to post that.

 

[fredriks]

A simple fact? No, more like a miracle. Could you show us a kite that can fly without string?

This is not relevant in regard to humbers ramblings but it is possibly that a kite without a string could fly like a paraglider or sailplane, i.e. gliding but still flying.

 

[John Freestone]

Taking a one second off two minutes, is brown underpants time, yet someone can take off 42 seconds. Unbelievable.

The trick is to keep the wheels off the tarmac at all times.

 

[RossFW]

This is not relevant in regard to humbers ramblings but it is possibly that a kite without a string could fly like a paraglider or sailplane, i.e. gliding but still flying

Sure, but it would do so whether there was "Real" wind or not, and, in the absence of any type of vertical current, "Gliding" necessarily involves the loss of height. Humber seems to think a kite magically "Gains power" from the wind and maintains altitude, even though it is at wind speed and therefore has no relative airflow.

 

[fredriks]

You are of course correct and that was the reason that I wrote not relevant in regard to humber.

I just commented on the non flying part as it feels like I am flying when being in the air 5-6 hours with my paraglider

I also doubt that most kites are going to fly with out the line due to stability problems but some might do.

 

[sol invictus]

http://www.aka.org.au/kites_in_the_classroom/student.htm

The faster the air moves over the upper surface of the kite the lower the pressure of that air becomes. As the air pressure above the kite becomes lower, the air pressure below the kite pushes the kite up in order to equalize the pressures above and below the wing. The greater the difference between the low pressure above the wing and the higher pressure below the wing, the greater is the amount of lift produced. In order for all this to happen, air needs to be moving over the kite. So what makes the air flow over the kite?

When we fly kites we use a string to hold on to the kite, and to prevent it from being blown away by the wind. Birds move through the air by flapping their wings, while powered aircraft use an engine to push the air towards the back of the plane fast enough to make the aeroplane move forward. The force that makes something move forward through the air is called thrust. Birds use muscle power to develop thrust, and except for gliders, aeroplanes use motors. A kite cannot produce its own thrust, and instead must rely on being held in place while the wind moves past it. So the thrust that acts on a kite is produced because the kite is being held in one place by its string while the wind flows around the kite. If there was no wind a kite would only fly if the person holding the kite string started running, making their own wind as air started flowing around the kite.

http://www.skratch-pad.com/kites/fly.html

Think of the kite as a sail boat, catching the air. The air tries to push the kite along like the sail boat. But the string the flyer holds keeps the kite tethered. Since the kite cannot go with the wind flow and the kite is tilted so that the air is deflected downward, the kite has no where to go but up.

http://www.letsflyakite.com/How.html

Thrust and lift are the forces that make kites fly. Thrust is created by the wind, so the speed of the wind affects how well a kite flies. Lift is produced when the bridle and line hold a kite at an angle to the wind. The correct angle causes the air to move more slowly across the face of the kite and pushes the kite upward. At the same time, air moves move quickly across the back of the kite and reduces pressure to create lift.

 

[Michael C]

http://www.ehow.com/how-does_4586488_a-kite-work.html

Kites fly because of two things: the flow of air around and over the frame of the kite; and the kite's resistance to that wind, which is provided by the string that is held by the person flying the kite. When kites fly, they are changing the normal air flow. They are blocking it, forcing the air to go around the kite. The air changes direction and speed as it moves around the kite, sending the kite up into the air. When a kite first meets the air, it deflects the air downward, which creates an upward force and lifts the kite. The air passing over the top of the kite is actually going faster than the air going under it. This fast air is creating less pressure than the air underneath the kite, which forces the kite upward.

http://www.plumcreekmarketing.com/articles/kite/kitefly.html

The kite achieves flight by virtue of its resistance to the wind provided by the string held firmly by the flier, and lift provided by the flow of air over and around the frame.

 

[fredriks]

I am surprised that sol invictus posted those link above. The pages are kind of correct but it is kind of misleading to involve the necessity of trust in regard to flying forward. I would say that all planes are able to fly forward without the use of the motor.

There are definitely kites that can fly forward without the use of the line. One example is a paraglider with or without a pilot. A paraglider can be used as a kite and flies forward by it self. It is of course gliding and loosing height when not towed.

Most kites probably don't have the stability to glide without the line but the links didn't say anything about stability.

edit: One more given similar links. Can't you guys instead show the error in my posts and explain the difference between a towed paraglider and a kite?

 

[sol invictus]

I am surprised that sol invictus posted those link above. The pages are kind of correct but it is kind of misleading to involve the necessity of trust in regard to flying forward. I would say that all planes are able to fly forward without the use of the motor.

There are definitely kites that can fly forward without the use of the line. One example is a paraglider with or without a pilot. A paraglider can be used as a kite and flies forward by it self. It is of course gliding and loosing height when not towed.

Losing height is the key there. If you lose altitude, you gain velocity wrt the air. That gives you a bit of lift - enough to maintain a controlled descent, but not enough to fly level (which really would be over unity). So eventually you crash or crash-land.

If you want to remain at fixed altitude, you need to either be held against the wind, powered so you can make your own velocity wrt the air, have access to an updraft, or be at air density for that altitude like a balloon.

edit: One more given similar links. Can't you guys instead show the error in my posts and explain the difference between a towed paraglider and a kite?

A towed paraglider is like a kite held by its string in the wind, so I'm not sure what you're asking.

 

[fredriks]

What you wrote is obvious and I have included that part in all my posts on the subject.

All I wrote was that gliding is also flying and that a kite might be gliding if you realize the line.

The lift is always almost equal to the weight by the way (L+D=mg) for steady state flying. To talk about a bit of lift in regard to gliding is misleading.

 

[Michael C]

I've found a wonderful resource about kite flying from NASA. The index is here:

http://www.grc.nasa.gov/WWW/K-12/airplane/shortk.html

Look at the page "Kite Launch and Flight", for instance:

It does not matter whether the air blows over the kite, or the kite is pulled through the air; the important factor for generating lift is the relative velocity between the air and the kite.

There's also a description of the forces on a kite.

And there's a really nice page on relative velocity.