Which is it?

true but the object is traveling through the exit at a given rate, so what stops it from continuing as it completely passes through the exit?

btw I concede that it's A I'm just curious

Gravity.

Gravity what? The cube is on the surface of the platform, it can't possibly slip off it. And the portal has no surface, so the cube can't slip off it.

Hmmm no he or she has a point - the exit is angled, if there is no momentum wouldn't it just fall right back through the portal?

in this thread

people who have only looked at one reference frame and are completely ignoring the other

Once the box is pushed to the lip of the receiving platform, it's resting on the surface of the sending platform, the local gravity takes over, and it falls off, as it's subject to the gravity and angle of its new location.

...as anyone who has moved from a horizontal to a vertical portal in this game knows all too well, that being a core mechanic.

It's B. As the cube is rebuilt at the exit portal, the freshly rebuilt matter will push previously existing material out of the way. It uses energy from the moving platform to accelerate the cube.

This is what I think but the general consensus is that we're wrong.

kek

A

Idiot tries to explain why its B

youtube.com/watch?v=eOBKIJ5dyHk

Well, things aren't rebuilt at locations, or it wouldn't allow FTL travel as demonstrated at the end of Portal 2. It's simply as if the two portals are a connected hole. The box at rest thus has no contact with the moving platform, as there's a hole in it. That hole happens to be moving, but as Glados says, portals do not alter acceleration, regardless of their momentum. Thus the box would still be at rest (if not for the fact that, in reality, in the game, the platform just jams up, since the platform velocity and the portal change aren't getting processed in the same frame.)

Does beg the question as to what happens when you use two different portals in radically different frames to each other though. If you walk through a portal on a comet barreling towards the sun at ungodly speed, and walk out into a room on Earth, for instance - do you retain your momentum and splattify on the nearest opposite surface?

>do you retain your momentum and splattify on the nearest opposite surface?
Yes - and you can demonstrate this in game fairly easily by being on a fast moving platform that pushes you across a portal it passes just underneath. You retain the momentum granted to you by platform's speed, at least until friction takes over (there's at least one puzzle where this phenomenon can result you going off a cliff into some acid).

But, apparently, even in that comet situation, you'll be fine, as long as your magic leg bracers are on (and there's no pool of acid).

In OP's puzzle, however, the box is never touching the moving platform and thus has no additional momentum. If the platform it was resting on was moving upwards, granting it energy, however, the result would be different.

You faggots
If you want a real answer, then this is impossible as universe cannot move relative to itself
You can answer this is you only use classical physics and which case, i quote Glados: "A speedy thing comes in, a speedy thing comes out".

So do the air molecules also move at the speed they were movin before passing through the portal

I'll think about it once portals are invented.

I believe it is explained that air molecules do not pass through portals, for, reasons.

3:15 upto 4:15 has a point though..

you can't really have a door with one end moving and the other end not moving though.that's why you can't cleary reason what would happen.

the answer very much depends on the properties of that hypothetical "doorway"

A because the cube lacks velocity to speak of

B is obviously the only consistent answer.

If an object enters the orange side of the portal at a speed of (say) 1 meter per second, it must come out the blue side at 1 meter per second. This means that velocity *relative to the portal surface* is preserved. If the piston moves down onto the cube with 10 meters per second, the cube moves through the portal at a speed of 10 meters per second, and therefore comes out the blue side at 10 meters per second. Anything else would mean the object got compressed in passing through the portal.

Wtf nigga. Didn't you play portal 2? In the end the rooms air is sucked into the moon.

There's a big gaping hole in the downward moving platform. Portals do not affect momentum. Momentum of objects, or lack thereof, is conserved. Thus, it shouldn't move anymore than if the descending platform was a hollow cylinder.

looking into Portal B the cube has plenty of velocity to speak of ;)

this

a cylinder where one end is moving and the other end is stationary.

ie. none at all. At best, you'd get some vibration in the box if the cylinder hit the lower platform hard enough.

True that... Glados does state this at some point though, that there's some sorta 'membrane' involved.

>none at all
huh?! none of what

also, how'd you explain the vibrations part?
just above the cylinder you'd still have a cube shooting out. so it'd have to be B

>Portals do not affect momentum. Momentum of objects, or lack thereof, is conserved.
Do you even know what momentum is, bro? Because this ain't it.

Like velocity, momentum is a relative quantity. There is no such thing as absolute momentum, but only momentum of an object relative to some other object. In scenario A, the momentum of the cube relative to earth is preserved; in scenario B, the momentum of the cube relative to the portal is preserved. "momentum is preserved" in both cases, including in my explanation in , so Glados' remark can't distinguish between the scenarios at all. My point in explains why momentum relative to the portal surface must be preserved.

>There's a big gaping hole in the downward moving platform.
That does not affect my point at all.

I'm saying if you take the portals out of the scenario, and instead had a large hollow tube, the cube would not move, provided the object it was resting on did not move from the impact.

Portals create a magic hole connecting two points without affecting momentum of objects that pass through them, regardless of their own, thus the situation should remain the same, save that the box is now at a new location with new angles.

If portals transferred momentum relative to objects not passing through them, then the box would continue to move relative to the orange portal, regardless of its connection to it. Thus, you could move the orange portal 45 degrees after the box moved to the blue portal, and the box would react accordingly, simply because it moved relative to the original surface the box was on. Needless to say, this doesn't happen. Therefore, there is no reason to assume the box is going to magically gain a relative momentum to the original platform simply because the orange portal is moving, anymore than it would if there were no portals involved, and the piston was simply a tube.

An even more obvious point is depicted in pic related. This scenario is one that definitely happens in the game, and in fact the one for which Glados explains that momentum is preserved. But you will note that momentum and velocity relative the the earth are *not* preserved -- while Chell maintains her /speed/, momentum and velocity include a *direction* of movement, and Chell's direction of movement relative to the earth changes in this scenario. Her direction of movement -- and thus, velocity and momentum -- *relative to the portal*, on the other hand, ARE preserved in this scenario.

Which makes it very clear that momentum relative to the portal is preserved, but momentum relative to the earth is not, even in situations that actually happen in the game. Which means A is clearly wrong and B is clearly right.

When moving from a horizontal portal to a vertical one, angular velocity changes, but not total velocity. There's no change relative to the portal, save in angles and location. An object with zero velocity retains that velocity, only the action gravity is placing upon it changes a result of the new angles, therefore A is right.

Reminder that there is only one instance of a moving portal, in which it is travelling sideways and you can barely interact with it. Any other scenario is pure speculation.
>b-but that one video where the guy is crushed by portals
Not in the base game. There is a reason portals are almost always stationary - they seem to be a nightmare to implement in the engine so making them do pretty much anything other than what they were intended for cannot be seen as representative.

>if you take portals out of the scenario
>instead had a large hollow tube, the cube would not move
obviously, but this is not what this is.

the tube metaphore is very lacking, exactly because both ends of a tube move in synchrony.
do you see the problem?

There's only one end of the tube involved in either scenario. Portals, in all instances, react as doorways, save that the exit of the door doesn't have to share the same angles or locations of the entrance. There's no reason to think this scenario would be any different.

Granted, in the games, the only instance of a moving portal we see is its interaction with another portal moving on another plane, with a laser passing through. In that instance, however, the laser does not exhibit any change, save in angle.

>only one end of the tube involved in either scenario
what the fuck are you even saying?
you can't have only one portal!

and the point earlier still stands, with whatever speed the cube enters the orange portal it must exit the blue portal with the same speed. so (!) when it exits the second portal it must have the momentum of the orange portal.
you can't deny that

It's still passing through one doorway, it's only that the doorway's exit is elsewhere.

The cube has no speed. It does not gain speed from a tube being moved over it, anymore than it does from a portal being moved over it. Portals do not grant their momentum to objects that pass through them, thus it's the same as if the object passed through a moving door or a moving tube was passed by the object. Slow thing in, slow thing out, regardless of the speed of either portal.

Not the other guy. I agree with you that B is right due to relative motions. But let's imagine the cube has a mass of 1 billion times the mass of the sun and with one litre of gasoline I could make the platform move the required distance to reach the cube at 50 metres per second. That would mean that with 1 litre of gasoline I would be able to make that very heavy cube fly at the speed of 50 m/s

The reference frame gradually shifts from flat surface to angled one.

When the cube enters the portal, it can start moving.
It will start moving to the side on the flat surface.
On the angled one, the movement will be along the surface, downwards.
When the movement starts, depend on the friction of the flat surface. The cube will never be on the angled surface, due to it being obstructed by portal – we can view it as a hole – it generates no force on the cube. The cube is in free fall from the perspective of angled surface frame.

Once the cube passes portal more than halfway, it can tip on its edge and *plop* as in answer A, which is correct.
The answer assumes similar gravity forces on both sides of the portal.
If the exit side were unaffected by gravity forces, the cube would stay in place on the angled surface – the answer still being A, but cube wouldn't slide nor *plop*.

The reason, that flat surface doesn't push cube like in answer B, is that once the cube passes the portal fully, the force of flat surface on cube will be nil. Before it fully passes, it will be negated by the mass of the cube still on the side of the portal with flat surface.

The mass of cube is distributed between both sides, depending on how big part passed the portal. I.e. cube passing in 1/3 will have 2/3 vs 1/3 mass distribution on both sides, passing in half – 1/2 vs. 1/2, fully – 0/1 vs 1/1, etc.
The force will be changed alike, as depicted by graph.

>people arguing over the mechanics of an event horizon attached to a solid object

You all realize the gaping hole in the physics here, right
There is no correct answer because a platform moving toward an event horizon would pass through it, not push it along.

one "doorway" with one moving end and a stationary end. not a door or a tube. that's why you're wrong.

interesting. hmm yes?
maybe how much mass passes through the portal would effect the energy you need.

and.. let's look at the moment that the cube is halfway through. on the second half you'd have the "blue room"-gravity pulling the object to the side a little bit. and the first half pushing through would effect the second half how exactly?!
we don't know, because this is a hypothetical.
we can't know.

it's the "doorway with a moving end and a not moving end"-thing. however that's supposed to work would effect the outcome.

On the contrary. A is right and B is wrong. The object and the portal do not form a system, and they never interact with each other. If the cube is stationary, it can't come out of it with a momentum it never had. The Portal does not ever exert a force on the cube, and thus the cube can't possibly end up with a speed at the other side.

you fucking A sayers x) the object passes through the portal. it gets ported from one place to another and you're trying to tell my "they never interact with each other".

i'm out. PLS SOMEONE INVENT PORTALS

Fuck is there a problem with physics or are are too stupid? I'm starting to consider the first one.

Portal never exerts any force on the cube.
It does not interact with it in this way at all.
The only thing it does, is changes its reference frame.

No one invented portals, because they do not follow laws of physics. I don't think anyone will ever invent them.

Let's pretend the portals are wormholes. According the meme physicists those are theoretical possible so there must be a theoretical answer to this problem.

Portals are fucking intangible. You can't grab a portal, you can't kick a portal, you can't exert force on a portal and a portal can't exert force on you. You can pass through it like a door, gate or hole to another room, but it doesn't have any mass, it is literally just a distortion of gravity, time and space to act as an synchronous link between two surfaces.

Definitely B.

Ok the object as no momentum when passing through the blue portal. However after passing it, it get momentum from the speed the platform gets while it keeep going from yellow portal to blue portal.

SO IT"S B MADAFAKA.
However maybe with the parabola as to take into account the change of gravity orientation and the initial moment, where the momentum is 0. However there is a huge discountinuity with the momentum that we can see as shifted heaviside function.

But this nigga It doesn't make sense energetically.

I know nothing about wormholes.
Here I explained how portals work There's high probability that if wormholes existed, they would be just like a portal. A hole that doesn't generate any force nor doesn't exist in material world.

Matter constantly moves, even on atomic level, so it could randomly "jump" through the window, to the other side, which could seem like if the hole affected it in any way. It is not the fact – if the other end was vacuum nor had any gravity – it's almost impossible for any matter that passes, to return back. It would simply retain it's velocity, lose all acceleration, and continue to drift straight away from the hole.
Nota bene, it's most likely what happened, when in Portal 2 the portal has been opened on the Moon. It created a window, some matter passed, and created vacuum on the initial side, which created very strong forces *on the initial side*, which accelerated matter towards the portal.
There's an experiment working on very similar premises, that you can try on your own. By hitting neck of the bottle filled with liquid, you can cause bottom to fall off. The hit creates cavities, small "bubbles" with very low pressure (almost like vacuum). The water that tries to fill this space, starts moving at very high speed in very short time, which creates force strong enough to break the bottle. The effect is called cavitation. Pic related.

What we do not know, however, is how wormholes could affect forces. I.e. if gravity from one end, could affect gravity on the other end. In this regard, we can only speculate.

>so what stops it from continuing as it completely passes through the exit?
The fact that the portal stops. As you just said, the portal has no momentum.

>>It doesn't make sense energetically. portals doesn't make sense energetically anyway sionce you create a discontinuity in the momentum which mathematically imply the use of distribution function and therefore a non conservation of energy in the classical frame

>some matter passed, and created vacuum on the initial side
wouldn't then be always like that moon or not ? you plebe

The problem with this is it requires us to think of hypothetical properties for the portals. If I remember right, in the game it doesn't let you put portals on moving surfaces except for that one time when you use the laser to cut that gas dispenser thing. This makes sense because if both portals are moving then the issue of this thread is brought up. In my mind the issue is whether the momentum remains consistent relative to your frame of reference at entry or at exit.
One interesting thing in the game is that you can put a portal on the moon even though the moon is moving relative to the earth, yet when you go through the portal you don't go soaring off into space, which means you must have adopted the velocity of the exit portal.
If this were to remain consistent in other situations of the game it means that your motion relative to the frame of reference in the exit portal is the same as your motion in the entrance portal's frame of reference. So even if you were on a comet plummeting towards the sun, as long as you're stationary relative to the comet, you shouldn't splat on the wall when you walk though, because your momentum RELATIVE to the portal hole stays the same. Logically, if you were to walk back through the portal you would once again adopt the velocity of the comet. By this same logic, if you were floating by in space somewhat stationary relative to the earth and the comet brought the portal to you at 20000mph you would indeed splat on the wall.
I vote for B.

>if you were floating by in space somewhat stationary relative to the earth
By that logic, you aren't stationary, you're moving WITH the earth, and therefore, not stationary relative to the other side of the portal. In OP's scenario, the object is both stationary relative to the earth and stationary relative to the other side of the portal.

No, because if both sides have similar pressure, the passing matter would push some other matter back, due to higher pressure.

If what you are talking would normally happen, you could cause decompression in your own room, by merely blowing outside open a window.

The force generated by vacuum is not strong enough. Or more correctly, the countering force is strong enough to neutralize the effect.

If the portal "fluid" had viscosity, you could relate it to the change in energy. So the cube could accelerate as the platform decelerates.

>>No, because if both sides have similar pressure, the passing matter would push some other matter back, due to higher pressure.
that's why you're a plebe, if they have both pressure you don't create a vacuum on the first side.

Portals are 2 ways bro of course this is a question of pressure, you're a plebe not because you were wrong on your vacuum moon description, but because you assume it was a portal property. Get you shits together, portals are juste like a fucking hole between 2 frames. That's how it's programmed in the game and how it works.

Any science fiction bullshit you come out of it in moon animation is actually just a fucking fiction, the animation is a fiction, not a game physical engine simulation, get your shit together mate

What are you doing in a thread about fiction, then?

If you read the thread, or OP at least, you would notice this thread is about relativity and hypothetical portals, not the portals as programmed in the Portal games.
Your comments are completely out of topic. Ad hominem arguments do not make your remarks any more relevant.
Nowhere in the post you refer to was stated, that any of that is property of a portal. The assumption that a portal/wormhole is just a hole was stated at least two times in my post.
It's you, who should get your reading comprehension together.

What would happen if I threw the blue portal like a Frisbee, and the cube went through the orange portal?

The same thing that happens, when you jump inside a moving vehicle.

I said 'somewhat stationary relative to earth' to imply that your motion is generally the same to the extent that your momentum wouldn't change drastically upon going through the portal
the issue is frame of reference, not location