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The Impossible Physics Problem

Ziggurat said:
No. It's a very bad question to give to such people. It is far too complex a scenario. It does not distill the essence of that concept into something easy to understand. People who do not understand the relativity of movement will not be enlightened by the problem, they will just get confused.
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Most likely, yeah.
 
*°°°°

Accommodation was box adrift in ocean. No bathroom facilities. Laser rangefinder provided. Would not book again.
 
Robin said:
I don't understand a word of what he is saying, but even if it is right it is certainly much too complicated for a lay understanding this at a classical level.
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Thanks for your posts! Yes you excellently summed up the practical end of ‘how can you figure out what is rotating vs what isn’t’ and described how it can, similarly to relative linear motion, ‘look’ baffling in the same way, until you test it. And that’s the practical difference: with rotational motion you can find out what’s ‘really’ moving, with linear motion you can’t, it’s frame of reference all the way down.

The spoilered post is just talking about how physicists hammer on the question of how/why does it do that. And yeah that it’s basically about rotational forces being imparted by rotational acceleration and that is the thing that’s, practically speaking, the system’s rotational frame of reference, in a way that the linear acceleration that imparts linear motion, doesn’t have a frame of reference ‘of its own’.

I think.

ETA: I wasn’t saying how do YOU know, I was saying how does IT know. What is different in a system where the space station is spinning and the camera is still vs a system where the camera is spinning and the station is still. Not how you can test it but why the test is different in the two different conditions. And it seems to be the relationships between the rotational forces of the total system. Ish?

The rotation itself is/creates a frame of reference.

The very physical constraint (whether it is a rope between buckets or gravity between celestial bodies) that causes rotation is therefore the spatial axis along which the effective potential energy function is NOT FLAT, and that's why it is the basis of the natural frame of reference for rotating systems. The natural frame of reference of the potential energy volume is the potential energy parameter which is constant - the radial vector.
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Or I guess to put it more simply, and also basically what a couple posters said already, is that a spinning thing is chock full of forces acting on one another, in a way that a linearly moving thing is not.
 
I just know some bastard is going to redirect the course of a speedboat to plow through our boxes to save one other box.
 
It's... complicated. Well, it is if you want to go GR on its ass. The moon basically doesn't really have any force acting on it, it just moves in a straight line... which happens to loop around because space itself is curved.

It's one of the reasons why I don't think it's really a good illustration for anyone who isn't already ok with relativity. The deeper you dig into it, the more things really aren't like in the boxes in the sea example. Starting with why the laser range finder would get you different results than an echo finder. That difference could actually tell you how fast you're moving relative to the air, incidentally.
 
PhantomWolf said:
Here's a simple appearing and yet impossible physics problem that you can give to people that have trouble understanding that all motion is relative.

...

Using the above information, determine how fast your box is drifting through the ocean, and in which direction.
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You are right, but not in the sense you mean. Since all motion is relative, and you can only measure the motion with respect to the boxes, you can only determine the motion relative to the boxes. Since you have not specified the motion of the boxes relative to the ocean, there is simply no way to determine the drift rate of the box through the ocean.

For that matter, since you have not specified the motion of the boxes relative to each other, it's not clear what, if anything, can be deduced.

Or are we supposed to assume, without any evidence, that the other boxes are stationary with respect to the ocean AND to each other?
 
PhantomWolf said:
Here's a simple appearing and yet impossible physics problem that you can give to people that have trouble understanding that all motion is relative.

You awake to find yourself in a box. Inside the box with you are a stopwatch, a compass, and a laser range finder. The box has a small slit set halfway up and in the centre of each of the four walls. Peering through these slits you can see that you are adrift on an ocean, with nothing in sight except for another four boxes, each one only visible through one of the four slits.

Using your compass you are able to determine that the box is orientated so that the walls are to your north, south, east, and west. Using the stopwatch and rangefinder you are about to determine your change in distance to each of the other boxes over the course of a minute. These are as follows. Multiple checks show that this change is consistent.

The north box -3m
The south box +2m
The west box +4m
The east box +1m

Using the above information, determine how fast your box is drifting through the ocean, and in which direction.
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While it is certainly possible for one to determine how fast and in which direction one is drifting through the ocean, however this problem simply does not provide one with the data that is needed to answer such a question.

After all, it is probably likely that some combination of both the surface winds and the surface currents are responsible for the change of positions of the boxes.

However, without a good more data and/or time, then it is impossible for one to determine one's drift speed and direction simply based on positional changes from nearby objects that are determined over the course of one minute.
 
WhatRoughBeast said:
Ah. Sorry. I meant the 4 other boxes. Obviously they are moving with respect to the "question box". But presumably the question assumes that those 4 are stationary in the water.
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Don't think so. Can you explain how they could be with the numbers given?


With the numbers given you can actually calculate their relative motion to each other.

BTW I'm presuming that since the boxes don't drift out of view of the slit that is meant to simplify the problem and imply that there is no "sideways" motion in each view.
 
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RecoveringYuppy said:
Don't think so. Can you explain how they could be with the numbers given?
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Qualitatively, maybe. Probably not quantitatively, but frankly I don't care enough to do the work to determine one way or another.

The trick is to reexamine the assumptions which popped into my mind, and probably into yours.

Each of the 4 reference boxes is visible through a slit in a wall which can face either north, south, east or west. This does not remotely specify that each box is due north, south, east or west. In fact, each box can theoretically be somewhere in a 180 degree arc centered on the reference direction. Then movement produces a range change which is modified by trigonometric considerations. Furthermore, there is no requirement that all the boxes are at the same range. In this case, let's say that the observer is moving more or less easterly and somewhat northerly. The "western" box is pretty much due astern, and the other boxes are to lesser or greater degree abeam of the box. The different angles, combined with differing ranges produce differing range changes.

That those range variations will change with time is not a problem. The problem stated, and PhantomWolf has confirmed, that the changes are consistent, not constant. That is, the range changes are consistent with the geometry of the boxes.

Like I say, I'm just too lazy to do the work needed to determine a geometry which would fit the numbers, or to establish that no geometry works. I suspect the latter, though.

With all that said, I suspect that PhantomWolf is having a bit of fun with us. It's been 5 days, and he has not revealed the answer to the question he posed, and he stated that the answer was "simple". Now he's sitting back and watching as the discussion goes all philosophical.

So, how about it, PhantomWolf? Tell us the simple solution, and explicate how it proves your point.
 
RecoveringYuppy said:
You know exactly as much about the other boxes as you do about the one you are in.
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That solves the problem. If I know that I, the range-finder, the compass, and the stopwatch are in this box, then I also know that I, the range-finder, compass and stopwatch are in the other boxes. This means that as I'm in all the boxes simultaneously I must be in a quantum superposition with an incredibly wide probability distribution regard my position. By Heisenberg's Uncertainty Principle I must therefore know my velocity to a very high precision.

QED
 
sphenisc said:
That solves the problem. If I know that I, the range-finder, the compass, and the stopwatch are in this box, then I also know that I, the range-finder, compass and stopwatch are in the other boxes. This means that as I'm in all the boxes simultaneously I must be in a quantum superposition with an incredibly wide probability distribution regard my position. By Heisenberg's Uncertainty Principle I must therefore know my velocity to a very high precision.

QED
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I was thinking along these lines, but your description is way better than anything I could have come up with. :thumbsup:
 
sphenisc said:
That solves the problem. If I know that I, the range-finder, the compass, and the stopwatch are in this box, then I also know that I, the range-finder, compass and stopwatch are in the other boxes. This means that as I'm in all the boxes simultaneously I must be in a quantum superposition with an incredibly wide probability distribution regard my position. By Heisenberg's Uncertainty Principle I must therefore know my velocity to a very high precision.

QED
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Well, no. By Heisenberg's Uncertainty Principle you can know your velocity to a very high precision, but that's not the same thing at all.
 
WSW, closer to the north box- now.

The comparative speeds can't stay the same unless the other boxes are moving too.

Unless you are falling on a parachute.
 
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