Weekly discussion 24 (1/13/13-1/20/13): $1 trillion coin

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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Valhallen » Mon Jul 16, 2012 2:39 am

Hmm. I think that this may warrant a bitchin' visual aid.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Q.U. » Mon Jul 16, 2012 6:10 am

The problem with A is, that the moment the cube is going through the yellow portal, it appears coming out of the blue one at a certain speed, and since blue portal doesn't start/stop moving, the velocity cannot be simply left, can it? The rate at which the cube will be popping out of the blue portal would be equal to the speed of the yellow one, I'm not sure the cube can then stop moving at that same speed relative to the stationary blue portal. In all fairness, if it was the cube being thrown into the yellow portal at that speed nobody would argue against B, and I think whether it's portal moving or the cube moving, due to interchangeable frames of reference both situations are equivalent.

So if the yellow portal is moving it becomes a moving frame of reference if we choose it in relation to the stationary cube. But then we have to make an assumption that all of the reality along with the blue portal is also the same frame of reference moving with the same velocity. So even if you think the cube has no momentum B would be the correct answer. The cube moving in case B is equivalent to the whole reality (the rest) moving in the opposite direction with the same speed, to compensate for the movement of the yellow portal.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Mir@k » Mon Jul 16, 2012 7:34 am

It's A.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Marquis de Soth » Mon Jul 16, 2012 11:18 am

I'm terrible at physics but it's A mainly because I assume this:

Warbear wrote:Putting a portal on a surface is equal to putting a hole in a wall.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 4:51 pm

Q.U. wrote:The problem with A is, that the moment the cube is going through the yellow portal, it appears coming out of the blue one at a certain speed, and since blue portal doesn't start/stop moving, the velocity cannot be simply left, can it? The rate at which the cube will be popping out of the blue portal would be equal to the speed of the yellow one, I'm not sure the cube can then stop moving at that same speed relative to the stationary blue portal. In all fairness, if it was the cube being thrown into the yellow portal at that speed nobody would argue against B, and I think whether it's portal moving or the cube moving, due to interchangeable frames of reference both situations are equivalent.

So if the yellow portal is moving it becomes a moving frame of reference if we choose it in relation to the stationary cube. But then we have to make an assumption that all of the reality along with the blue portal is also the same frame of reference moving with the same velocity. So even if you think the cube has no momentum B would be the correct answer. The cube moving in case B is equivalent to the whole reality (the rest) moving in the opposite direction with the same speed, to compensate for the movement of the yellow portal.

No.

The momentum and velocity of the portal does not effect the cube in any way. The portal is like a hole in a wall that goes to a different location. The portal doesn't act upon the cube in any way, shape, or form.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 4:52 pm

This is all irrelevant anyway, because you can't put portals on moving surfaces.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 4:58 pm

Image
Imagine, if you will, that the black line is a piece of paper with a hole in it. The hole is just big enough to allow the cube to pass through it.

Image
The cube would pass through the hole in the paper, no matter how fast the piece of paper is going. The hole in the paper does not act upon the cube at all, because it is an empty space. Nothing touches the cube but the ground it rests on and nothing acts upon it, so it sits stationary as if nothing happened.

Now replace the hole with a portal and it's the exact same thing with a slight variation.

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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Q.U. » Mon Jul 16, 2012 5:03 pm

There is one thing that makes this explanation seem a little off, and why the statement that portals can't work on moving surfaces is more relevant here.

Imagine the cube is going through the portal, take a high speed recording of it, you will see that the cube is going into the yellow portal with a certain number of cm per second being taken into it. This means it will be coming out on the blue side at the same rate. Keep in mind that at the blue portal it is only the cube that is moving, and it is moving out of the blue portal at the same speed at which the yellow portal is shoved on it.

Portal physics just isn't compatible with real physics.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 5:04 pm

It is completely compatible with real physics, you're just over-thinking it.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Q.U. » Mon Jul 16, 2012 5:06 pm

Maybe I am indeed.

Well I must put my mind to rest, so I'll go ahead and run the test myself.

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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 5:06 pm

Warbear wrote:This is all irrelevant anyway, because you can't put portals on moving surfaces.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 5:12 pm

no reason you can't put a portal on a stationary surface and then push a button to make the surface move
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 5:14 pm

You've played the games, right?
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 5:20 pm

yes, and I know there's never been an instance where you do that. but that doesn't mean it can't be done in a world where portal guns actually exist!
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Mon Jul 16, 2012 5:21 pm

Riz wrote:yes, and I know there's never been an instance where you do that

There has, actually. Many times. Any time you place a portal on a surface that can move, as soon as it moves, the portal is destroyed.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 5:23 pm

wha
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 5:27 pm

I honestly don't remember placing a portal on something that wasn't moving and when it moved the portal disappeared, refresh my memory
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Calek » Mon Jul 16, 2012 5:28 pm

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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Princess » Mon Jul 16, 2012 5:31 pm

The moon moves. :3
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 5:34 pm

oh snap
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby NeoWarrior7 » Mon Jul 16, 2012 5:36 pm

I just assumed the portal has to be stationary so it's moving from one distinct point to another. The portals are controlled by the gun, so I assume the gun can't process fast enough to handling moving portals.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Mir@k » Mon Jul 16, 2012 7:34 pm

I don't get it. Speedy thing comes in, speedy thing comes out. You can, then, assume that when a stationary thing comes in, a stationary thing will come out, even if the portal was moving.

Assuming portals could move, this would be scenario B:

Image

Which doesn't make little bit of sense to me, the portal is moving, the thing is not. Momentum does not simply pass from one object to another unless there's a transfer of force, like if a high speed object bashed a stationary object. Pardon me for my erroneous wording regarding physics terms but english can go suck my donkey cock.

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Portals are just holes. Therefore:

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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Riz » Mon Jul 16, 2012 7:38 pm

woof woof nigga
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Warbear » Tue Jul 17, 2012 2:00 am

Thank you, Mirak, for the much better visual representation of how physics works.
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Re: Weekly discussion 21 (7/15-7/22): Arguing with portals

Postby Valhallen » Mon Jul 23, 2012 12:02 am

Protip: keep track of the acceleration and trace it to the forces that cause (or should cause) the motion invoked. Some people are invoking a sudden deceleration without apparent cause. Let's say that the speed involved here is 10m/s. What result we get depends on how we model the situation, so let's look at some different possibilities.

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Real-ish (particulate) momentum - Objects are made of a large number of particles, each with its own momentum. When each particle of the weighted storage cube passes through the portal, it is moving with respect to the blue portal's reference frame, and so the weighted storage cube continues to move once it exits the blue portal unless interfered with. Since the circumstances don't supply such interference, the weighted storage cube flies out of the blue portal in what will become a parabolic arc.

Image

Game (parametric) momentum (object point model) - "Parametric point momentum" - The object is a digital model composed of geometric data and numbers that describe such things as mass, speed, rotation, etc. Such information is applied to a point in the center of the weighted storage cube to simulate a particulate real-ish object without needing the extra computation to simulate the greater complexity. When the object's physics point passes through the portal, the next physics time interval updates the weighted storage cube's speed, momentum, etc. with its new reference frame of being pushed diagonally by the surface it had been sitting on. Therefore, when the weighted storage cube passes fully through the portal, its momentum is expressed as a certain parametric value that describes its now-fast movement, which will result in a parabolic arc as with the particulate model.

So how can we get result A?

Image

Game (parametric) momentum (object space model) - "Parametric space momentum" - The weighted storage cube's data for mass, speed, rotation, etc. are not attached to an internal point, but rather to the reference frame that it occupies. So long as part of the weighted storage cube stays within the orange portal's reference frame, that frame is used to calculate those values. Only when the portal is fully passed are new values calculated for the weighted storage cube's data. In this case, the first physics tick in the blue reference frame sees the weighted storage cube on a slanted, stationary platform (stationary because its motion stopped the previous tick). Whether it sits there, slides down, or rolls off depends on the coefficient of friction and balance of the setup.
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