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

[Clive]

<snip>

Re your solution to my problem: I think you've misinterpreted what I've tried (badly no doubt) to say. (The problem is probably not worded as well as it could be - I got it from someone else but rewrote the description from scratch here.)

I'm not comparing energies between the different reference frames - but instead looking at whether energy is conserved within each frame separately. In the first frame, I end up needing mgh = mv^2/2 (if total energy is to be conserved). That admits non-trivial solutions - for each positive value of h (and positive m also!), we can find two possible values for v (corresponding to the cart moving left or right) and so everything looks reasonable. However, with the second reference frame, there is no similar solution to the equation that I show at the end. Does that make "the mystery" any murkier?

Okay here is an even worse one for you if that one bothers you. Again two different systems an object is going left to right at v it has a rocket motor on it and doubles it speed to 2v. Its KE was mv^2/2 and now it's 2mv/2, a difference of 3mv^2/2. Our second system is moving with the object at the speed of v. Again the object changes its speed by rocket motor adding v to its speed (which was zero in this frame). Now its change in KE is mv^2/2. The first system seems to have gained more energy

You seem to have a typo after doubling speed to 2v: the KE goes to 2mv^2, not 2mv/2 as you've (accidentally no doubt) written. But even after that minor correction, I'm still not bothered! I am aware you can't compare KE values (or differences) across different frames and generally expect anything to line up.

 

[CORed]

No, the mistake is yours. See my reply, to SD.

Lots of nonsense. Adiabatic doesn't enter into it, as pressure doesn't change. It's just a big word that you don't know the meaning of that you threw in. The person and the air are all moving with the caboose. There is nothing to dissipate kinetic energy, no force to change the motion. The jumper will land on the mark whether he jumps 6 inches or 6 feet (assuming high enough ceiling. For that matter, even if he bounces off the ceiling, he will still land on the mark.

Of course, in the Humberverse, who knows what will happen?

 

[humber]

Humber,

Like I said, please just humor me- it should take a one-line answer-


Pulse Jet- 100MPH TAS into 100MPH Headwind. What is the groundspeed?

Why should I do that RossFW? How many times do I have to tell you that the problem with the treadmill has nothing to do with "equivalence"?
This is the last time.

You all really need to change the way you think about windspeed. What sort of instrumentation is used? Really...

Actually, your question is not well posed, but I am going to assume you mean that the plane is traveling at 100mph, w.r.t surrounding air in the simplifying case? Then w.r.t the ground it is stationary.

If this is going where I think it is...

 

[humber]

Lots of nonsense. Adiabatic doesn't enter into it, as pressure doesn't change. It's just a big word that you don't know the meaning of that you threw in.

I sometimes work in acoustics, I told you that. I was pointing, out once again, that your questions are too simplistic to be of any use in a real model.

The person and the air are all moving with the caboose. There is nothing to dissipate kinetic energy, no force to change the motion. The jumper will land on the mark whether he jumps 6 inches or 6 feet (assuming high enough ceiling. For that matter, even if he bounces off the ceiling, he will still land on the mark.

Of course, in the Humberverse, who knows what will happen?

Wrong, and the extensions make it worse. Try again.

 

[RossFW]

If the person jumps within the caboose full of air, then KE will be lost due to the vertical component alone.

OHGOD!!

(Hey! I'm channeling Janice from friends!!)

Do you all understand the impact of what he is saying?

He is saying that because the person jumping up and down in the caboose dissipates energy in a number of ways he will loose KE (Because, as we all know, in the Humberverse KE is STRICTLY relative to the earths surface) and start to move relative to the caboose.

How can anyone who even knows as many scientific terms as Humber have so little grasp of even elementary school physics?

Actually, your question is not well posed, but I am going to assume you mean that the plane is traveling at 100mph, w.r.t surrounding air in the simplifying case? Then w.r.t the ground it is stationary.

It would be easily understood by anyone with a very basic of understanding of aerodynamics. Yes, 100MPH through the air is 100MPH True Air Speed. That's the standard nomenclature.

You all really need to change the way you think about windspeed. What sort of instrumentation is used? Really...

Sir, I use windspeed and it's consequences on real world aircraft every day of my working life. You might be interested to know that, prior to the invention of navigation systems such as Omega and INS, there was NO WAY to measure the wind in an aircraft in flight. All you could do was infer it by seeing how it affected your track and groundspeed vs your true airspeed and magnetic heading.

Cause, you see, in the FRAME OF REFERENCE of the aircraft RELATIVE to the air around it, the ground plays no part and has no consequence. I can jump up and down in my aircraft all day, and never end up pinned to the rear bulkhead!!!!!

Now lets go on- What is the TAS of a Hot Air balloon in zero wind? (Hint, it's a ROUND number!!)

 

[spork]

I sometimes work in acoustics...

No you don't

 

[sol invictus]

Wrong, and the extensions make it worse. Try again.

I'm embarrassed to admit this, but I'm shocked by the utter and total ignorance of the most basic principles of physics you've just displayed. Embarrassed, because you've made mistakes this elementary hundreds of times in these threads, and yet I still haven't learned not to be surprised.

You're the new Dunning-Kruger poster boy...

 

[humber]

You keep using that word. I do not think it means what you think it means.

// CyCrow

I am often told that in this forum, as if it were so. I need no dictionary or thesaurus, and the words come readily to mind. It is not only words, but many other things. No chance any of you could be wrong!

This is what I meant;
inconceivable; Unable to be mentally conceived of; unthinkable, unimaginableE17.

"Of course, nobody can do what is inconceivable to you, Spork, but you do produce the inconceivable."

(1) Spork cannot conceive that others have done what he has not. (anyone)
(2) He produces a cart that is not of his conception. (Bauer et al)

Anyway, I would like to ask you a question, please. What do you think "equivalence" brings to the cart, that ignoring it would not?

 

[RossFW]

Anyway, I would like to ask you a question, please. What do you think "equivalence" brings to the cart, that ignoring it would not?

Good question, actually, because, in fact, the answer is- Nothing.

The vector diagram for the cart will reslove itself from any frame of reference, including you sacred, one and only frame of the earths surface. From that POV, you have a cart in stationary air on a moving surface.

What we have spent half a lifetime telling you is that this MODELS AND PREDICTS the carts behaviour with the opposite set of conditions (Staionary surface, moving air) as it invol;ves the differential movement of two media, and that for that purpose it doesn't matter which is still and which is moving.

But obviously we are wrong......

 

[Subduction Zone]

You seem to have a typo after doubling speed to 2v: the KE goes to 2mv^2, not 2mv/2 as you've (accidentally no doubt) written. But even after that minor correction, I'm still not bothered! I am aware you can't compare KE values (or differences) across different frames and generally expect anything to line up.

Yes Clive I had a typo, and you saw quickly through what was a nonproblem. I am still thinking about my answer to your problem, I may have answered a bit too quickly. Of course I could always try to channel humber for a unique answer. Maybe humb (who is the champion humber channeler ) can give it a shot.

 

[spacediver]

Ooops! Here is a good example. Oxygen masks are tethered, SD.

If the person jumps within the caboose full of air, then KE will be lost due to the vertical component alone. But what you are telling me is not right. What stops the body from being displaced? The air? The usual friction to the floor being optional? Not at all necessary?
I could go on. Is the displacement such that the air can be considered adiabatic?

What happens to a balloon floating in a car as the driver accelerates?

Are you being purposefully dense?

We're talking about ZERO acceleration here. Constant velocity. You understand that if a plane is going at a steady velocity it is NOT accelerating, right?

If I toss a balloon directly upwards in the cabin, it will drop down right into my lap without moving horizontally at all.

 

[spork]

No chance any of you could be wrong!

You're the one with the PhD in statistics. What do you suppose the chance is that ALL of us are wrong on everything we've said for the past few thousand posts - and that you alone are right?

 

[Dan O.]

Because you tried to introduce a tether.

WELSHER WELSHER humber is a WELSHER!


When you loose a bet you need to pay up, not make excuses. You shall forever be strung on that tether.

 

[RossFW]

Spacedriver-

You haven't been to Humberversity 101!

Here's how it goes-

Nothing can be in motion without a force applied to it (Now now, just because every Phd in the world is howling in his wheaties that that is wrong, doesn't change the World of the Humber!!)

Anything with a force applied to it is accelerating (He read THAT on HIS wheaties box, he just didn't understand it)

Therefore anything moving IS accelerating.

Oh- and KE is exclusivley measured with reference (sorry, sorry, there's no such thing as reference err.....)

KE is exclusively measured with "THINGY" to the Earths surface, which makes it a bitch to calculate for the Vesuvians, but that's their problem.

Got it now? there will be a quiz after lunch!!

 

[Subduction Zone]

Clive I think I will stick with my original statement.

I think the problem is more how the respective energies were defined in each case. In both cases potential energy was changed into an equal amount of energy change in kinetic energy.

 

[humber]

I'm embarrassed to admit this, but I'm shocked by the utter and total ignorance of the most basic principles of physics you've just displayed. Embarrassed, because you've made mistakes this elementary hundreds of times in these threads, and yet I still haven't learned not to be surprised.

Sol_invictus, humble in embarrassment.

You're the new Dunning-Kruger poster boy...

Now this is going to be fun.
Are you suggesting that if this experiment were actually performed, that the person jumping could do so to the height of the caboose, (and even hit it) and then land exactly in the same spot on the floor?

 

[RossFW]

Now this is going to be fun.
Are you suggesting that if this experiment were actually performed, that the person jumping could do so to the height of the caboose, (and even hit it) and then land exactly in the same spot on the floor?

Only in the real universe. you know, the one that can send a space-probe to the outer limits of the solar system with incredible accuracy using our flawed concepts.

Clearly not in yous....

 

[humber]

WELSHER WELSHER humber is a WELSHER!

Na Na Na Na Nah!!!

ROFL

 

[Modified]

Are you suggesting that if this experiment were actually performed, that the person jumping could do so to the height of the caboose, (and even hit it) and then land exactly in the same spot on the floor?

Yeesh. Have you never been in a moving vehicle?

 

[sol invictus]

Now this is going to be fun.
Are you suggesting that if this experiment were actually performed, that the person jumping could do so to the height of the caboose, (and even hit it) and then land exactly in the same spot on the floor?

Dear god.

Where have you been for the last 500 years, humber?