I has confuse

Doomination

Doomination

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1305739843758.jpg



So I was lurking a bit today and saw this, and I feel like an idiot for asking, but which is correct?

Basically the portal on the top left of the picture is on a platform that slams down onto the cube, with the blue portal on a slanted brush, which the cube then comes out of obviously.

I feel like it SHOULD be B., but I believe A would occur in the game.

thoughts?
 
B should occur, but I'm not sure if the engine is based on object momentum relative to the world or relative to the portal it travels through.

I don't even remember there being portals on moving surfaces in the game; is that even supported?
 
I would say A. I think there is a point in the first portal where something like that happens and you just pop out on the other side. Granted, the piston wasn't moving much and the portal was on a immobile surface.
 
I'm no physics buff whatsoever, but going by "Speedy thing goes in, speedy thing goes out" I'd expect "A" to occur (in the game).
 
B is correct. There is no such thing as an absolute measurement of velocity, only relative velocity. There is no difference between the portal moving towards the object or the object moving towards the portal. They will produce the same result.
 
I tried to make a simple map in the new portal 2 map editor, but failed to find a way to make the piston, since it's been 2 years since i've touched hammer. Oh well. The world may never know
 
David.Seth2 said:
Wouldn't it be A? The box has no momentum
Click to expand...
Momentum relative to what? There is no such thing as just "having momentum". Velocity and momentum are relative measurements. You say it has no momentum, but it's on the Earth which is spinning, rotating around the Sun and hurtling through space. When you say it has no momentum what you mean is, even if you don't realise it, that it has no momentum relative to the Earth.

There is no difference, from the point of view of physics, between you approaching an object at 20mph or that thing approaching you at 20mph. It's just different perspectives. Whether the portal is moving towards the box or the box is moving towards the portal from your point of view, from the point of view of the portal the box is moving towards it with a certain velocity and momentum. Which is moving relative to the Earth is entirely irrelevant.

Edit: Of course what I just said does not actually apply in-game. In the Source engine their is an absolute measure of momentum, because programming it any other way would be retarded and overly complicated. So if you were to do it in the game engine it would be A, but to do it in reality (if such a thing as a portal existed) it would be B.
 
You can make a simple one using a func_door entity, by default A will happen, but B can be forced to happen if you wish it to.

Edit: Assuming the engine even lets you move a portal along that particular axis, I have never tried myself.
 
ríomhaire said:
Momentum relative to what? There is no such thing as just "having momentum". Velocity and momentum are relative measurements. You say it has no momentum, but it's on the Earth which is spinning, rotating around the Sun and hurtling through space. When you say it has no momentum what you mean is, even if you don't realise it, that it has no momentum relative to the Earth.

There is no difference, from the point of view of physics, between you approaching an object at 20mph or that thing approaching you at 20mph. It's just different perspectives. Whether the portal is moving towards the box or the box is moving towards the portal from your point of view, from the point of view of the portal the box is moving towards it with a certain velocity and momentum. Which is moving relative to the Earth is entirely irrelevant.
Click to expand...
However, once the box pops out the other portal, does it have any innate movement? No, it's been sitting still, and will remain still.The speed of the orange portal doesn't mean anything, it only changes how long we have to wait for the box to come out the other one. Speedy thing goes in, speedy thing comes out. The box is stationary, the portal is moving.

edit: is this a new version of plane on treadmill
 
Replacing my post because I thought of an example of a moving portal in portal 2: when you cut off the vents/whatever going into the neurotoxin generator, it requires placing portals on the wall panels that move horizontally along so you can cut them with the laser.
 
kineaesth said:
However, once the box pops out the other portal, does it have any innate movement? No, it's been sitting still, and will remain still.The speed of the orange portal doesn't mean anything, it only changes how long we have to wait for the box to come out the other one. Speedy thing goes in, speedy thing comes out. The box is stationary, the portal is moving.

edit: is this a new version of plane on treadmill
Click to expand...

Are you talking about in terms of the game or in real life? The box definitely has speed in relation to the portal. That's all that should matter. But in the game the only speed objects can have is relative to the world, so in this case it's none. Picture looking at the box through the blue portal. The box would appear to be rushing at you. Do you really expect it to just stop as soon as it goes all the way through the portal? That would make no sense. I don't get why you say 'speedy thing goes in speedy thing comes out' when that directly contradicts the rest of your post. Speed is relative, not absolute.
 
I'm going to have to think more about this >_>
 
Riom don't get confused. Everything you said is right. The only reason the answer to this is A is because of the engine's difference to real life physics.
 
Vegeta897 said:
Riom don't get confused. Everything you said is right. The only reason the answer to this is A is because of the engine's difference to real life physics.
Click to expand...
No I'm talking about this with another physics student here and she makes some decent points. From the Earth reference frame the box as no momentum in the initial situation so it should have no momentum as it is transferred to the portal. Also in the initial state the only forces on the cube are gravity and the reaction force of the surface it is sitting on. The portal cannot enact a force on the cube as it is just a window frame for the cube to travel through. The only forces on the cube as it goes through the portal are still this reaction force which will not increase and the altered view of gravity. There is no force to push it out.

Seth and KA are right but the reasons are a little more subtle than they stated.
 
You're complicating things too much. Let's not forget that we're talking about fictional technology here. Portals could not exist in real life since they defy the laws of physics, (they can result in perpetual motion) Objects can also have movement and no movement relative to the same thing. Depends on which side of the portal it's on.
The cube gains its momentum the moment it starts passing through the portal. This momentum is on the blue portal's side, because on the orange side it's still just sitting there. Already this is defying the laws of physics.

Think about the scenario I posed with looking at the cube through the blue portal. It would be moving through the portal at a very high speed, what force is stopping it once it gets all the way through the portal?

If you throw a cube through a stationary portal, it obviously is going to fly out the other portal. But it doesn't matter that the cube is moving in relation to the world, it matters that it's moving in relation to the portal. You could have the cube just floating still in space, and the entire world could be moving around it, and if it goes through the portal it's still going to have that momentum.
 
I've always thought of the Portal as simply not interfering with the momentum of an object, rather than somehow recording and preserving the momentum or whatever. Essentially having no impact on it what-so-ever. When I look at that scenario, I see it as being more like lowering a frame around the cube.
 
I'm going to have to make a flash animation to demonstrate this, aren't I?
 
Vegeta we were thinking about it wrong. First of all, can a portal really be said to have any momentum? it is not an object and has no mass (technically speaking electromagnetic fields have no mass but still have momentum but I'm getting getting off-point here). The portal is not really an object. It is a link between two points of space. As you said yourself depending on which side of the portal you are on the momentum you have is totally different. This pretty much proves that considering the momentum relative to the portal is useless. The portal is not an object nor a field and it cannot exert a force on the cube. The force is coming from nowhere. A is correct. I we were both wrong. I'm making another diagram to help show this.
 
I never said the portal had momentum. I said the cube had momentum relative to the portal, that is, the world inside the portal. As the cube travels toward, through, and beyond the portal, it retains its momentum relative to the world inside the portal, which it is now in.
 
ah, so I'm not the only one that found this confusing.. I feel a bit better now :)
 
KA sorry I didn't explain my reasoning better, but I was at work (shame on me) and I don't have a good grasp on physics in general. Never studied it :( Anyway, I was thinking about this way today (which could be totally different than the original scenario presented):
98FQD.jpg


so if a panel fell onto someone, with a panel having a portal on opposite sides, and it landed on the person, would it send him flying through the air? or would they still be standing still in the same spot, with a panel around them?

I always felt that 2 portals linked were basically the equivalent to an open window. If I jump through the window I will be on the other side without any outside force caused by the window. But if an open window was dropped on me while standing still, the window will just land around me. Again, I dont know if this is a proper way of looking at it. Plus, I'm not considering what the game engine would do. I'm trying to theorize this as if it was real life.
 
David.Seth2 said:
But if an open window was dropped on me while standing still, the window will just land around me.
Click to expand...

But we're not just talking about dropping a window frame on you. You have to remember that on the other side of the portal is a moving world, a world that is moving in relation to you. And so if you are thrown into that world, you are going to have momentum.
 
Vegeta897 said:
But we're not just talking about dropping a window frame on you. You have to remember that on the other side of the portal is a moving world, a world that is moving in relation to you. And so if you are thrown into that world, you are going to have momentum.
Click to expand...

I get what you are saying, but if a portal is being dropped onto you, wouldn't that in a way be making that world on the other side moving onto you too? Damn I wish I was better with creating visuals. Or explaining my (limited) thought process.
 
David.Seth2 said:
but if a portal is being dropped onto you, wouldn't that in a way be making that world on the other side moving onto you too?
Click to expand...

Yes, that is exactly what I said. The world moving in relation to you or you moving in relation to the world are the same thing.
 
The forces don't need to 'change'. There don't have to be ANY forces on the box. This could be in space for all I care.

You're not taking into account that through the portal is essentially another world, because it does not have the same relation to the box as the current world it is in does. The box isn't moving in relation to the world it is in before entering the portal, but it definitely is moving in relation to the world inside the portal, because that world is essentially approaching the box, because the portal is approaching the box. The box maintains this momentum as it passes through the portal. Now it's in the second world where it had momentum, and it's going to keep it. The fact that the surface the orange portal is on is moving is where this momentum comes from.

Picture being inside a train. Relative to the train, you are not moving. But relative to the outside world, you are moving. If you step off the train, you're going to have momentum relative to the ground. You don't just 'stop' because you're no longer on the train. You had momentum relative to the ground outside the train. You could say that the ground and the train are like the two 'worlds' on each side of the portal. Just like the box just doesn't 'stop' after it finishes moving through the portal.


EDIT: Another example. Picture this:


1GEOZ.jpg



The box is balanced on a long pole. The orange portal is still on the piston moving downward. It keeps moving downward down the length of the pole.

What will you see coming out of the blue portal?

yNS4F.jpg


You'll see the box on the pole rushing through. Moving relative to the world it is now in (you can't tell me it isn't), but still stationary to the world it WAS in. When the piston portal stops moving down, the pole will stop and the box will fly off the pole because it has momentum.

Once the situation reaches what it is in my second image, it's no different than if you were holding a pole with a box balanced on it, and you jerked it upward. The box flies off it.
 
my brain hurts

edit: Vegeta that analogy makes sense, I'm just not sure which is true now.
 
I originally thought it was like dropping a window on a box (it will go in one side and out the other with no momentum) however if one side of the window wasn't moving then it would be like a tunnel where you pull one side of the tunnel down onto a box. The box is then stuck inside the tunnel.
BUT in this situation the box HAS to move because it cannot be stuck inside the tunnel.
Therefore if it has to move to get out of the blue end of the tunnel why wouldn't it move with all the momentum of the orange end of the tunnel.
 
This really comes down to a fundamental disagreement between whether a portal's momentum relative to an object is converted into the object's momentum upon exiting the other portal. I personally agree with everyone talking about it being relative to the world - to my mind the velocity at which the portal is moving does not translate to the object moving through the portal, so it would be like lowering a frame like someone said, where the only thing affected is the speed at which the object materializes (with no momentum/speed besides the change in the angle of gravity) through the portals.

Unfortunately this debate isn't really resolvable. The idea that a portal's momentum towards an object which then goes through the portal is reflected in the object's momentum is basically equally valid as saying it doesn't, just because they're two ways to interpret the game's physics (since there is no possible real world reference to this situation).
 
Ennui said:
Unfortunately this debate isn't really resolvable. The idea that a portal's momentum towards an object which then goes through the portal is reflected in the object's momentum is basically equally valid as saying it doesn't, just because they're two ways to interpret the game's physics (since there is no possible real world reference to this situation).
Click to expand...

I disagree, I don't think there's any other way to look at this as far as what is involved in this experiment.

Did you look at my pole example? The pole and box are clearly moving after they pass through the portal, why would the box suddenly stop just because the portal stopped? That makes far less sense than it retaining its momentum. Whether you are flying at the portal or the portal is flying at you makes no difference.

If it magically stopped then you would also be saying that you stop if you jump into a portal, which we all know you don't.

Edit: Welp, here's a little flash animation that can perhaps demonstrate how ridiculous this 'other interpretation' looks:

http://www.pixelatomy.com/stuff/portals.swf

Look at that and tell me which one makes more sense. It helps if you only focus on the blue portal side.

The only way the situation on the right makes sense is if the box is welded to the pole.
 
I like the animation, it makes sense. But I still see it as the world coming down on you vs you going up into the world. meaning, if you were to be going up into the world, we would get the result as seen in the flash you made. but the world coming down (since the portal is lowering onto you) makes me still think that you wouldn't go flying off. But I by no means have the knowledge to back up my claim, so if anyone with a good grasp of physics could confirm/deny any of the hypothesis posted in this thread it would be a help
 
Here is another example, since Riom was talking about forces and such.

http://www.pixelatomy.com/stuff/portals2.swf
(in this case, the box is welded to the pole)

Where is this plank getting its energy from? If the box has no momentum, how is it making the plank move?
 
Portals don't just create momentum, something has to be moving through it already for it to be propelled out the other side, surely? The portals just change the world around the object.
 
Let's look at this example in space.

Orange portal is on a platform moving to the right through space, toward a line of floating cubes. Blue portal is stationary.

n8DV3.jpg



Box is halfway through both portals. The half-box coming out of the blue portal has motion relative to the world. The other half doesn't.

hXWfg.jpg



What my opposition is saying is that the box will 'stop' moving relative to the world once it passes all the way through the portal, because it was never 'moving' in the first place (even though we can clearly see it is moving. It can bump into that plank, causing it to move)

P7cON.jpg


When the orange portal reaches the next box, what happens? Well, it's clearly going to push the first box out so that it can come through the portal, no?

Ct6OK.jpg


Once that happens, the pushed box will retain the momentum it was given by the second box and keep floating through space. The second box would do the same thing the first box did and stay there at the edge of the portal.

iwJLV.jpg





I think this is wrong. I think the boxes would emerge from the blue portal at the same speed they enter the orange, and keep moving through space. There is no reason for them to just 'stop' coming out of the portal just because they are all the way out.

This is what should result:

z1BSB.jpg


The boxes float out of the blue portal, retaining their original spacing, except now moving in the opposite direction but at the same speed as the orange portal.
 
As in, the object going through the portal.
 
You guys are thinking about this way too much. The problem goes from being a box on a level surface to a box being on a slope. The box contacts nothing which would change it's mass or velocity. It is simply re-oriented and re-positioned in accordance with the angle of the blue portal.
 
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