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

[humber]

Sigh. Back to the avoidance routine again, humber? Maybe you could flesh out your reasons for not being able to answer these two simple questions. Probably not, there are no reasons, just excuses, and weak ones at that.

It's not avoidance, Mender. It is pointless to continue this line. You have my general argument for that drag/load condition. That chutes have load lines, and this governs their behaviour, is not accepted by you, so any numerical examples are not useful.
The general case always stands, because the force available to all parachutes and balloons falls as their velocity increases w.r.t the wind, whereas loads increase with velocity.

 

[humber]

No, he just doesn't care for or about knowledge. Having difficulty understanding the world about him, yet he shuns any means by which it can be explained. It is a selfish and belligerent attitude, but ok provided he never has to do anything which would materially affect someone else.

Like reading tissue paper.

 

[John Freestone]

Why do people keep describing it as "accelerating" due to "gravity" at g m/s/s? Why was it all right to discuss objects accelerating towards terminal velocity before, and no-one said "No, they're not accelerating."

John, it's quite simple. Sometimes we don't use an inertial reference frame to discuss motion. Since we live in an accelerating world, we tend to use a reference frame that is also being accelerated at 9.8 m s^-2 away from the earths center. From our accelerating reference frame, we describe the motion of a ball tossed into the air as being accelerated by gravity instead of the reality that we are being accelerated towards the free floating ball by the repulsive force of the ground we stand on.

Accelerometers are generally ignorant of our chosen accelerating reference frame so they measure acceleration with regard to their own inertial reference frame and therefore claim that they are being accelerated when at a fixed point on the surface of the earth.

Thanks, Dan. It is becoming simpler, and it's not exactly that I didn't understand or had never heard this GR version of events. My question was not meant as "How is it possible to describe things that way?", but "Why, after quite a lot has been said about the adequacy of classical mechanics to describe such things as elevators or thrown balls, is it now not adequate to do so?" (and I'm getting lectured like I never heard of Einstein). Your replies, like others', are fine answers of the first. I specifically asked the second a few times.

Let me put it this way: yes, Dan, that's quite simple boggled. However, classical mechanics is simpler. In that view, a ball resting in your hand feels the force of gravity, opposed by the normal force, and when thrown, after you accelerate it upwards from rest (w.r.t. you) with your muscles, gravity accelerates it downwards as soon as it leaves your hand. It describes just the same path as in the less simple version ... y'know, give or take. Interestingly, this is simpler both from a normal intuitive human point of view, but actually helps make sense of two people on either side of the earth throwing balls, or everyone doing so. The strange idea "the reality that we are being accelerated towards the free floating ball by the repulsive force of the ground we stand on", raises the question of how points on the earth can all be accelerating outwards away from its centre by that repulsive force, yet apparently not get any further away from each other, while this is the explanation of how they meet up with the ball?

"Gravity is weird" is the sporkian answer that I like very much. Einstein's General Relativity is weird, too. It may be "the reality" like you say. It may be just another physical theory. It might be a theory that is better than classical mechanics for some purposes, and much more extensive. It applies when c.m. does not, when masses and velocities are very large. We were discussing elevators and stuff, not black holes.

I just find this movement of goalposts rather interesting, from c.m. to Relativity, after humber was bashed several times with the assertion that you don't need anything besides c.m. for these problems.

I find it interesting that you are now trying to imagine in what circumstances you could not distinguish a gravitational field from acceleration, and have dug yourself a nice spherical hole in a homogenous sphere.

However, assuming your "reality" is right, then my objection to Michael's assertion is answered. It does, however, seem a very sudden jump he made from c.m. to the walls of a building accelerating upwards, yet not getting anywhere, past a non-accelerating elevator. I'd have just mentioned it in passing, you know, like "according to Einstein..." so we knew what the new game rules were.

 

[mender]

It's not avoidance, Mender. It is pointless to continue this line. You have my general argument for that drag/load condition. That chutes have load lines, and this governs their behaviour, is not accepted by you, so any numerical examples are not useful.
The general case always stands, because the force available to all parachutes and balloons falls as their velocity increases w.r.t the wind, whereas loads increase with velocity.

The point is that your argument is wrong. Avoiding it is stupid. Your loss.

 

[mender]

The general case always stands, because the force available to all parachutes and balloons falls as their velocity increases w.r.t the wind, whereas loads increase with velocity.

Here's yet another one, Dan. There will be more later, assuming that humber keeps posting.

 

[mender]

1) A parachute is tied to the ground in a 30 ft/s wind. For an arbitrary parachute size, the tension on the tether is say 100 lbs. What will the tension be in a 60 ft/s wind?

2) A parachute is attached to a 100 lb load and is falling through the air at a steady 30 ft/s. What will the steady state speed be if the 100 lb load is replaced with a 200 lb load?

Can you please just respond to those two questions?

Well, these two "impossible" questions seem to have stumped humber, anyone else want to give it a try?

Humber, I'm sending you a PM with "my" answers so you can compare to whatever anyone else posts here if you want. Ask me questions with a PM if you like but I'm done responding to you here.

 

[Dan O.]

So we're up to 80 pages almost entirely dedicated to humber's extreme wrongness. Can we make it to 100?

The only limiting factor will be if humber gets himself banned for not abiding by the Membership Agreement, rule 12 in particular.


I created the "Where humber is wrong" list specifically because a number of posters had started resorting to personal attacks and the list was to help focus the attacks against humbers arguments instead of humber himself. For the most part, this strategy appears to have been successful.

Actually debating the items on the list is temporarily on hold as I am ignoring most of what humber says due to the continued use of insults on his part. In the mean time, the list continues to grow and everyone else appears to be learning a thing or two about physics.

 

[humber]

Well, these two "impossible" questions seem to have stumped humber, anyone else want to give it a try?

Humber, I'm sending you a PM with "my" answers so you can compare to whatever anyone else posts here if you want. Ask me questions with a PM if you like but I'm done responding to you here.

I told you I was not interested, Mender. You insist in comparing apples and pears. Drag chutes are designed for maximum drag, they do not make efficient hauling devices. Wind turbines obey fan laws as I said, and of course increase output with increasing velocity. That is why both find use for those purposes.
A wind borne object's force, decreases with velocity, while an attached load will increase with velocity, so windspeed will not be reached.
This is true even if both load lines are simply linear with velocity.

 

[RossFW]

Not interested.

...In learning ANYTHING!!

 

[humber]

The only limiting factor will be if humber gets himself banned for not abiding by the Membership Agreement, rule 12 in particular.

I created the "Where humber is wrong" list specifically because a number of posters had started resorting to personal attacks and the list was to help focus the attacks against humbers arguments instead of humber himself. For the most part, this strategy appears to have been successful.

Yes, purrrely for that reason.

Actually debating the items on the list is temporarily on hold as I am ignoring most of what humber says due to the continued use of insults on his part. In the mean time, the list continues to grow and everyone else appears to be learning a thing or two about physics.

Out and about marking your territory.

 

[semper]

I told you I was not interested, Mender. You insist in comparing apples and pears. Drag chutes are designed for maximum drag, they do not make efficient hauling devices. Wind turbines obey fan laws as I said, and of course increase output with increasing velocity. That is why both find use for those purposes.
A wind borne object's force, decreases with velocity, while an attached load will increase with velocity, so windspeed will not be reached.
This is true even if both load lines are simply linear with velocity.

Make a drawing of the load curves and show us, include your rabbit etc. Specify the operating point of the system as you perceive it. Find a photograph of a balloon crew with their hair blowing back in the breeze. Look up equilibrium. Back up your assertions.

 

[RossFW]

Make a drawing of the load curves and show us, include your rabbit etc. Specify the operating point of the system as you perceive it. Find a photograph of a balloon crew with their hair blowing back in the breeze. Look up equilibrium. Back up your assertions.

And do one of your Kite/Drouge system while you are at it!

 

[humber]

I find it interesting that you are now trying to imagine in what circumstances you could not distinguish a gravitational field from acceleration, and have dug yourself a nice spherical hole in a homogenous sphere.

You can always tell one from the other.

Miicheal_C is incorrect when he says that the body's organs will not sense the acceleration of free-fall under gravity. The body is not a homogeneous mass, but is made of masses suspended by muscle, ligament, or viscous coupling. These objects will move at different rates under acceleration, until a some internal mechanical limit is reached. That they do not relax, would be evidence of continuing acceleration.

The gravitational field of a large mass has a gradient. Objects, moving or otherwise, are subject to a slightly different force according to height above the surface. A long object in free-fall in a vacuum will be subject to stress along its length, and as there are no infinitely stiff objects, that will always be present and detectable.

 

[humber]

Make a drawing of the load curves and show us, include your rabbit etc. Specify the operating point of the system as you perceive it. Find a photograph of a balloon crew with their hair blowing back in the breeze. Look up equilibrium. Back up your assertions.

Did some of that a long time ago, though I am not so foolish as to regard excursions of human follicles as substantial evidence.
Since you have made no contribution other than simpering irony, why don't you make the drawings? Back up your assertions.

 

[Dan O.]

So the straight dope is here: when we're talking about the "frame of the ground", the "frame of the treadmill" or the "frame of the wind" we are not talking about real inertial frames in the strict sense.

Actually we are because the measurement frame in those cases is one dimensional and orthogonal to the acceleration of earth's gravity. Newton's equation of motion still applies.

However, when the treadmill is tilted, our reference frame is then accelerating due to a component of gravity and this has to be taken into account if we are going to apply Newton's laws. The correction is usually in the form of a force equal to the acceleration factor times each mass.

 

[semper]

You can always tell one from the other.

Miicheal_C is incorrect when he says that the body's organs will not sense the acceleration of free-fall under gravity. The body is not a homogeneous mass, but is made of masses suspended by muscle, ligament, or viscous coupling. These objects will move at different rates under acceleration, until a some internal mechanical limit is reached. That they do not relax, would be evidence of continuing acceleration.

The gravitational field of a large mass has a gradient. Objects, moving or otherwise, are subject to a slightly different force according to height above the surface. A long object in free-fall in a vacuum will be subject to stress along its length, and as there are no infinitely stiff objects, that will always be present and detectable.

Sure Humber, I should be able to feel that right now, especially if standing up, maybe that is why it is so easy for humans to fly blind with no instruments, no-one ever gets spatial disorientation in Humberworld, all the expensive instruments and instrument flight training is a scam.

 

[humber]

So the straight dope is here: when we're talking about the "frame of the ground", the "frame of the treadmill" or the "frame of the wind" we are not talking about real inertial frames in the strict sense.

Actually we are because the measurement frame in those cases is one dimensional and orthogonal to the acceleration of earth's gravity. Newton's equation of motion still applies.

However, when the treadmill is tilted, our reference frame is then accelerating due to a component of gravity and this has to be taken into account if we are going to apply Newton's laws. The correction is usually in the form of a force equal to the acceleration factor times each mass.

The cart's equilibrium is upset by the force of gravity. There is sufficient and renewable energy available from the momentum of the propellor, to power the resultant motion. It would be difficult to build the same case for a real cart. That is, to explain how gravity could accelerate the cart up hill.

 

[humber]

Sure Humber, I should be able to feel that right now, especially if standing up, maybe that is why it is so easy for humans to fly blind with no instruments, no-one ever gets spatial disorientation in Humberworld, all the expensive instruments and instrument flight training is a scam.

An argument from insensibility. Does you proud.
Pilots blackout because their senses and organs fail, for the very reasons I stated. However, I don't imagine that you would feel anything in a fighter jet or an elevator, as both events would be in conflict with our apparently Chopra inspired view of reality.
No drawings forthcoming, I expect. Nothing concrete.

 

[semper]

Did some of that a long time ago, though I am not so foolish as to regard excursions of human follicles as substantial evidence.
Since you have made no contribution other than simpering irony, why don't you make the drawings? Back up your assertions.

Specify the axes. I might, I won't ever make as significant a contribution as Ascher Shapiro though, and nor will you. Anything I come up with will be based on the basic foundations which he elucidates with unusual clarity. It would save us all so much time if you would acquiesce and deign to be educated on the basic premises before vomiting your vitriolic incorrect postulations.

 

[Dan O.]

Wow!!

I think we've reached a water-shed now. We are having an informative and entertaining discussion of Physics, whilst simply ignoring Humbers nonsense!

Let's keep that going.

Dan,

I can model what you are saying, and in fact said as much to John. That being said, I share one point of confusion with him. Whilst I understand(and have experienced!) the fact that being in freefall is the same as being under no gravitational force, and that there is no way to measure acceleration in that state, you ARE accelerating from the frame of reference of the surface of the body supplying the gravity. How does the fact that in one case you have no acceleration, whilst in the other you do, square with acceleration being absolute?

While writing it occurred to me that, I suppose,from the frame of the surface the object is accelerating and therefore CANNOT be thought of as inertial frame, and from the frame of the object, the same can be said of the surface,.

Am I on the right track?

Yes Ross, we wrote extensively of reference frames on the earths surface being inertial which may have lead to some confusion because those reference frames were only dealing with horizontal motion. When in a gravitational field you have to account for the forces created by that field.

The inside the free falling elevator car can be considered an inertial reference frame because the acceleration due to the gravitational field is canceled by the acceleration of the car itself. This free falling reference frame cannot really be used outside the elevator car. Even inside the car, there are limits. If you had a very sensitive accelerometer it would not read 0 everywhere.

Take a look at spork's drawings and subtract the accelerations on the earth's surface from the accelerations due to the accelerating car. This will be the car in free fall accelerated by earths gravity. What you would have is a point near the middle of the car (specifically at the car's center of gravity) with 0 acceleration and everywhere else will feel a force pushing it away from that center point. In extreme cases such as orbiting too close to a neutron star, those residual forces can tear a ship apart or or squish the occupants against the outer wall of their General Products hull.