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

[Dan O.]

The purpose of this post is to present the established tenets of classical physics and to create a point where this thread can be split if there is still disagreement as to the validity of these tenets.

If the participants in this thread agree to the split, all further discussion of the validity of alternate inertial reference frames, the special nature of an earth based reference, the treatment of Kinetic energy being an absolute property of an object and not relative to the frame of reference and any other claims that invalidate classical physics shall be split to the new thread.
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Title: The validity of classical physics [split from Down Wind Faster Than The Wind]

In Newton's laws of motion, there is no factor of an absolute reference for position or velocity.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

First law

It is possible to select a set of reference frames, called inertial reference frames, observed from which a particle moves without any change in velocity if no net force acts on it. This law is often simplified into the sentence "A body continues to maintain its state of rest or of uniform motion unless acted upon by an external unbalanced force." This law is known as the law of inertia.​

Second law

Observed from an inertial reference frame, the net force on a particle is proportional to the time rate of change of its linearmomentum: F = d (mv) / dt. Momentum mv is the product of mass and velocity. Force and momentum are vectorquantities and the resultant force is found from all the forces present by vector addition. This law is often stated as "F = ma: the net force on an object is equal to the mass of the object multiplied by its acceleration."​

Third law

Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence "To every action there is an equal and opposite reaction."​

This means that we can investigate the behavior of physical systems in an equivalent inertial frame that is chosen to be more convenient. For instance, the physics of a vehicle traveling down a straight level road with a tail wind can be investigated by placing that vehicle on a similar surface that is moving at a constant velocity relative to the observer so that the same effective tail wind will not be moving relative to the observer and the vehicle when traveling at the speed of the tail wind will also not be moving relative to the observer.

This split thread has been created to discuss the validity of using alternate inertial reference frames to examine or model classical physical interactions [between the limits where relativity and quantum effects are significant] and related topics such as motion relative to the ground being somehow special and kinetic energy having a specific value independent from the frame of reference. I don't understand the contrary view so I'll let the other posters present their side.

Split from: http://www.internationalskeptics.com/forums/showthread.php?t=128483

Replying to this modbox in thread will be off topic  Posted By: Gaspode

 

[humber]

Assume a windspeed of 10 mph. Also assume a cart moving on the ground at exactly the same speed and direction as the wind.

1) What is the speed/velocity and the direction of the air relative to the cart?
2) What is the speed/velocity and the direction of the ground relative to the cart?

Edit:
3) What is the speed/velocity and the direction of the ground relative to the air? (or vice versa)

If you do something, and it doesn't work, do you do exactly the same again but hope that this time it will ?
When I tell you "true but trivial" and take your logic to show contradictions, and then ask "where does the KE go", or wonder how it can be that I am at at "relative" windspeed, yet literally doing so at the same time. You don't see those as perhaps problems with your ideas, but that I cannot do the simple arithmetic.

(1) How many "frames" in the world are there with zero KE relative to the treadmill cart? Aren't they the same vector?

(2) How many are there that do not?

(3) In all of the bullet-time experiments you could connect each item together, no? In fact, aren't all items in the same "frame" effectively one mass? What difference would it make if that were zero? How do you do any work without leaving that frame?

You have fallen for a simple mathematical error. Yes, it's correct, but the answer has no meaning or consequence. Lots of equations do that. Once you make that error, all sorts of wonders are possible. Over-energy and time machines are all "theoretically possible" in a limited sense.

The conclusion from the argument for zero KE is something like;
"Equivalency tells us that all objects are equivalent relative to themselves"

Step back, take a real world view of the treadmill.
In your new world of "frames" do you now see the items on the supermarket checkout belt as in a different "frame of reference", or just things moving relative to you? (Still have to pay, just the same)

I say person on a treadmill as someone moving relative to the ground. If I put myself on that same belt or as an observer, I say I am moving relative the ground. If you say no, you are making a mistake. You are using the ground perspective, but retaining it and transferring it to the treadmill. I think that you would say "relative to me, the ground is moving under me". No, it is not. ( That would certainly break the principle of locality, if nothing else)

What if I paint the ground, or illuminate it in some way that creates an optical illusion, so the the belt may appear to go one way or the other?
You may fall over, perhaps. Why? Because the "inertial reference" in your ears, the fluid-based balance system, is bound to the gravity of the Earth. It evolved under those conditions. Like your sight.
What if you overcome that? You still don't know which way things are going.
Perhaps you could look "under" the treadmill to avoid the trick, but "where" would you be so that you can so that? On the ground.
Instruments can show you your errors, but they are not allowed, it seems. Perhaps because they expose the deception.

JB's porch is a carnival stand. Let me put you in an enclosed box. When I later open the door, I tell you that you have been in the 14th Century. Try to prove to me that you have not.
How much weight do you think it would take to disprove that? I think that you will agree that it is not possible to say, because the ideas are not connected.
The weight over the wheels of the cart and "frames of reference" have that same relationship.

Do items flowing in a river reach riverspeed? Why not? If you have a power boat, don't you need constant force and energy to maintain riverspeed?
If you achieve riverspeed, is the water ahead and behind frozen in "bullet time" like windspeed air?

 

[John Freestone]

Cartoon questions have cartoon answers. Even still, the chance to yell 'false' lured some to error. It is irrelevant that KE = 0. True, but trivial.

It's not trivial if you're on the sharp end of the bullet. But really we just like to force you into admitting the opposite of what you stated earlier to demonstrate what a lot of nonsense you post.

Spork claimed that (ROLF), not me.

Ok. You mean ROFL, BTW, AFAIK.

I just saw that Dan posted his message a few minutes before mine. I'm for the split as Dan suggests.

I don't quite understand that. If you have questions about props and other details, why not post them, instead of saying that you'd like to but other people are swamping the thread with trivia about physics? You don't have to compete for thread space to discuss those things. It seems to me that without these discussions of inertial frames, there would be precious little keeping the thread alive. I also consider the question a very valid one, even if it is perhaps done to death now.

I am not even sure that it is done to death. I think there might still be a question hanging - which is whether there is any difference between mathematically analysing the same physical conditions from different frames (i.e. considering a different element as stationary), and constructing completely different physical scenarios, as per land test and treadmill test. I hope you're aware that I accept the equivalence in this case - I just don't quite get where the limits are to the principle. If it's ok to drive the 'ground', why would it not be ok to drive the wheels with a motor at a constant rate and see what happens to the air and the ground - or maybe it would.

 

[CORed]

No, it does not have zero KE relative to you. It has zero velocity relative to you.

And if you sqare that zero velocity and multiply it by the mass of the object, what value does that give you for the kinetic energy? Of course, I'm not sure what result multiplication by zero gives in the Humberverse.

 

[humber]

It's not trivial if you're on the sharp end of the bullet. But really we just like to force you into admitting the opposite of what you stated earlier to demonstrate what a lot of nonsense you post.

Make is a barrel of oil moving at 100m/s. How much error is your velocity will kill you?

Ok. You mean ROFL, BTW, AFAIK.

All that to tell me you took the meaning, but not that you wrongly attributed the claim of Chief Scientist to me?

 

[humb]

With this talk of frames and the denial of the ground reference, let us not forget that at absolute zero all motion stops. Where will your treadmill be then? An undeniable point of no motion and zero KE. Certainly if you are hit by a bullet at absolute zero in any frame, you would feel the effect, though it will of needs be hotter than that and therefore irrelevant. But it would shatter you like glass nonetheless.

 

[humber]

And if you sqare that zero velocity and multiply it by the mass of the object, what value does that give you for the kinetic energy? Of course, I'm not sure what result multiplication by zero gives in the Humberverse.

Exactly. The real cart has a "real and positive" KE wrt the ground. The translation from windspeed is -ve. So the KE is indeed "positive" wrt ground. It is not so on the treadmill. Keep up, I pointed that out a few posts ago, and much, much earlier too.

Velocity is a vector. A time-variant quantity. It cannot be described by one coordinate. Momentum is a vector, so that applies too.
Schoolboy error.

 

[CORed]

I mean that KE is a property of the body. It does not change with perspective.

In the Humberverse, being rear-ended by a car going 60 miles per hour when your car is stationary is the same thing as being rear-ended by a car going 60 milse per hour when you car is going 58 mph in the same direction. Or the opposite direction, for that matter. The Humberverse is a strange place for sure.

 

[humber]

In the Humberverse, being rear-ended by a car going 60 miles per hour when your car is stationary is the same thing as being rear-ended by a car going 60 milse per hour when you car is going 58 mph in the same direction. Or the opposite direction, for that matter. The Humberverse is a strange place for sure.

So things in your world are restricted to your frame. You contradict yourself.
The KE of two bodies may remain the same (relative KE = 0 in your terms)
but gain 1000 fold wrt another

 

[Christian Klippel]

In the Humberverse, being rear-ended by a car going 60 miles per hour when your car is stationary is the same thing as being rear-ended by a car going 60 milse per hour when you car is going 58 mph in the same direction. Or the opposite direction, for that matter. The Humberverse is a strange place for sure.

Hell CORed,

yes, indeed it would in the humberverse. But then, we couldn't have any cars or anything else, since we would have been smashed by the KE of the earth and all objects on it by now. I'm wondering "where did all the KE go" that the my house has, while sitting in it. In the humberverse, it should have smashed me as soon as i put a foot in it.

A strange place that humberverse is, indeed...

Greetings,

Chris

 

[humber]

Hell CORed,

yes, indeed it would in the humberverse. But then, we couldn't have any cars or anything else, since we would have been smashed by the KE of the earth and all objects on it by now. I'm wondering "where did all the KE go" that the my house has, while sitting in it. In the humberverse, it should have smashed me as soon as i put a foot in it.

A strange place that humberverse is, indeed...

Greetings,

Chris

As the designers at GM or Ford is they agree with you. Go on. Only an e-mail away. Ask you physics teacher.
You have evaded all the questions that I posted to you? Are you afraid to answer them?

 

[Christian Klippel]

As the designers at GM or Ford is they agree with you. Go on. Only an e-mail away. Ask you physics teacher.
You have evaded all the questions that I posted to you? Are you afraid to answer them?

You don't answer my questions, that came first, so don't expect me to answer yours, which came later. Play nice and other will play nice as well. Play foul and expect others to foul you as well. It's simple as that.

 

[humber]

You don't answer questions, so don't expect me to answer yours. Play nice and other will play nice as well. Play foul and expect others to foul you as well. It's simple as that.

I did answer your question. The answer is always something like you are killed or the KE is zero, but I did it again. If you post another question I will answer it, but you must defend it, and not assume you are correct.
If your version of the world is true, then the other questions should be easy.

 

[humber]

So, you agree now that in that case the bullet's KE would be zero relative to the person moving at the same speed and direction?

Yes, Told you many times. You just won't take yes for an answer.
True, but trivially so.

Wikki? What Wikki? But thanks for showing so clear that you don't even bother to read the links that people give you.

They do not answer the question, but reiterate it. I have quite openly said that I do not look at such link, after having done so. I already know what they will say, but of course they do not say that a treadmill is a frame of reference.

YOUR answer concerning the treadmill. How you support that, without simply saying KE = 0. I know that, but do you think that scientific truth is based upon one answer?

Again, do you agree that there is 0 KE in the bullet in that example?

[/QUOTE]
Yes, now go from there. Spork can't, but perhaps you can.



Originally Posted by Michael C View Post

For a ride-on DDWFTTW cart, what would be the best way to control acceleration and deceleration?

Change the prop's pitch, so that it is more efficient at that speed of travel.
Brakes waste energy, so store it instead. A rotating mass, as used in some "motorless" buses is the idea. When you have more that you need, you can use that energy to drive the propeller or wheels so that the cart accelerates. Given enough storage, and like the bus, the cart's speed can be independent of the wind. YoYo's give no power gain, so will not be effective.

 

[Christian Klippel]

Yes, Told you many times. You just won't take yes for an answer.
True, but trivially so.

No, you didn't. You answered:

No, it does not have zero KE relative to you. It has zero velocity relative to you.

And later you said:

The answer is always something like you are killed or the KE is zero

Now you say yes, it has 0 KE relative to me, if i move at the same speed and direction. So, you have been wrong with your first answer, and tried to wiggle out with your other answer. After all, there can't be "either this or that" at the same time for a single frame of reference. And here the frame of reference is the person moving along with the bullet, at the same speed and direction.

Let's get the basics right first. Do you admit that you have been wrong with your first answer? Yes or no?

They do not answer the question, but reiterate it. I have quite openly said that I do not look at such link, after having done so. I already know what they will say, but of course they do not say that a treadmill is a frame of reference.

They clearly say and imply that things like KE and velocity are relative. That in turn implies that there can be many frames of reference, not only one. And in case of the cart on the treadmill, the frame of reference is attached to the cart. It can also be the air, or the belt, but never the ground, because the cart has nothing to do with the ground in this case, only with the belt and the air. But more about that later, after we established some very basic things.

YOUR answer concerning the treadmill. How you support that, without simply saying KE = 0. I know that, but do you think that scientific truth is based upon one answer?

Yes, now go from there. Spork can't, but perhaps you can.

What you know or what not is exactly what is in question here. So, again, let's get the basics right first. Once you agree to the well established fact that KE and velocity are relative, and thus there can be different frames of reference, we can continue.

 

[spork]

Change the prop's pitch, so that it is more efficient at that speed of travel.

Another brilliant quote from humber. But I wonder how a prop can become any more or less efficient when it is nothing more than a simple flywheel in the humberian universe. Remember when we were going to replace the prop with a flywheel, an old rag, etc. and find that the cart was no less effective?

 

[humber]

Another brilliant quote from humber. But I wonder how a prop can become any more or less efficient when it is nothing more than a simple flywheel in the humberian universe. Remember when we were going to replace the prop with a flywheel, an old rag, etc. and find that the cart was no less effective?

Once gain with the straw man. You are a man of limited responses.
Are you saying that changing a prop's pitch will not affect its efficiency?
That with sufficient energy, the cart can not be driven directly by the wheels, even if the prop were to be in a vacuum?

 

[humber]

No, you didn't. You answered:


And later you said:


Now you say yes, it has 0 KE relative to me, if i move at the same speed and direction. So, you have been wrong with your first answer, and tried to wiggle out with your other answer. After all, there can't be "either this or that" at the same time for a single frame of reference. And here the frame of reference is the person moving along with the bullet, at the same speed and direction.

Let's get the basics right first. Do you admit that you have been wrong with your first answer? Yes or no?

I have told you that many times. It is trivially true. I can take your stance or not, because it remains so from both perspectives. The bullet does not have zero KE. The "relative to you" is what you add.
It is one thing to propose a cartoon world where things do not have real physical characteristics and there is effectively no time, no beginning or end, for the purposes of explanation, but not to then say that is the same as reality. That's the kind of mistake that is so ridiculous you will not find it mentioned via Wikki. Physics texts assume that the reader does not believe in magic, so they don't mention it.

They clearly say and imply that things like KE and velocity are relative. That in turn implies that there can be many frames of reference, not only one. And in case of the cart on the treadmill, the frame of reference is attached to the cart. It can also be the air, or the belt, but never the ground, because the cart has nothing to do with the ground in this case, only with the belt and the air. But more about that later, after we established some very basic things.

They do not support your interpretation. That is the point. If done, it leads to bullet time. If you post someone in support, you should ask the if they agree with the implied consequences, and not simply assume that they do. Spork cannot supply academic support, because they do not agree. It is to laugh...
Show me a link that directly shows that a belt can be a "frame of reference" and supports your conclusions.

In cartoon land, ride a rocket. It may have an engine or not. Without damaging the machine in other ways, cut off the tail. There it is, right "behind" to you, KE = 0. Pick it up, it doesn't weigh so much.
Do think that happens with real rockets?

What you know or what not is exactly what is in question here. So, again, let's get the basics right first. Once you agree to the well established fact that KE and velocity are relative, and thus there can be different frames of reference, we can continue.

No, I only agree that tow objects traveling at the same velocity can be "said" to have zero KE. It is mathematically correct, but had no physical meaning. It's "notional"

 

[Christian Klippel]

I have told you that many times. It is trivially true. I can take your stance or not, because it remains so from both perspectives. The bullet does not have zero KE. The "relative to you" is what you add.

Then any further discussion with you is just meaningless.

If you can not agree on basic principles that are used in physics over and over again, there is just no basis for any successful discussion. No, you can not "take my stance or not". You can not bend physics and the used math to solely support your viewpoint, just to make it fit. Two people discussing something have to agree on the terms, definitions and methods which are the basis of what is going to be discussed.

You are not willing to agree on such a simple set. Therefore it's absolutely meaningless to discuss it with you any further. The "relative to me" is not just simply added to make me happy, it simply defines the frame of reference that is used. A windtunnel test for an airplane works because these very principles allow for that. It work's even with the fact that the plane has 0 velocity and thus 0 KE relative to the ground. It would have that in case of a plane really flying. But still the tests work in the tunnel. You want to rewrite physics, go for it. Good luck with that, and hope that your employer will never come across this thread and finds out who you are.

I'm definitely done with you now. You had a second chance, you have choosen to insist on playing foul. I'm not playing your silly game anymore.

 

[humber]

Then any further discussion with you is just meaningless.

I'm definitely done with you now. You had a second chance, you have choosen to insist on playing foul. I'm not playing your silly game anymore.

None of that stops you from answering the questions, if only to show that you are not avoiding them. They are from your stance.