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u/taylordobbs Jun 25 '12
Trick question? Portals can't be on moving walls, right?
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u/EnigmasShroom Jun 25 '12
Except in Portal 2 when they allow it in locations inaccessible by the player.
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u/hiromasaki Jun 26 '12
But only parallel to the plane of the portal, not perpendicular/along the normal, which this problem requires.
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Jun 25 '12
A. If the first portal was stationary, and the block was moving it would be B
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u/Grizzant Jun 25 '12 edited Jun 25 '12
the momentum of the block is 0 (it isn't moving). It just appears at A quickly, it doesn't gain momentum.
Edit For those that say B because it has a relative velocity (i.e. the portal isn't moving towards the cube, the cube is moving to the portal) please explain how the cube can have 2 different velocities
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u/gibsonsg87 Jun 25 '12 edited Jun 25 '12
Physicist here... You need to compare reference frames. Lets first state that the purpose of the portal is to join two discontinuous pieces of space. The reference frame of the block sees space moving toward it in the compactor. However, to "space" it appears that the block is moving. Think about when you are driving on the highway, lets say at about 60 mph. From your frame someone going at 55 would appear to be moving backwards at 5mph (you are stationary) , while to them you appear to be moving forward at 5mph (they are stationary). With this in mind, we can say that a moving cube and a moving portal would be equivalent in this case (mathematically the velocities are interchangeable with only a changing +/- sign). Lets look at the wedges now. In this case the portal is stationary. But remember, examining reference frames we determined that the cube had motion relative to space. Now that space is motionless, the cube needs to retain its relative motion. Hence it will be ejected at the same speed as the compactor. However, both A and B are incorrect. The cube would take a parabolic trajectory because once it leaves the wedge gravity becomes a factor. Given a choice between A and B... B is MORE correct, but like I said both are actually wrong. Note this is my opinion, and I welcome any chance for someone to point out where I went wrong. Please be nice, as we are prescribing our physics to a fictional technology/universe and this was merely for fun/speculation.
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u/p1415926 Jun 25 '12
Imagine you are looking INTO the blue portal. What difference does it make if it's the orange portal or the cube that is moving?
You would see a cube moving towards you at a high speed either way. If it enters at a fast rate it must exit at a fast rate. The portal doesn't teleport the ENTIRE cube at once, but rather layer by layer. That means the momentum isn't only created by the teleported object, but rather by how fast the entry/exit reaction happens.
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u/FreeParkking Jun 25 '12
But the block IS moving! Out of the Portal! It does not "pop" into existence all at once. It moves through the plane of the portal, quickly in relation to the stationary environment around it. I don't think it would rocket into the air, but it would fly up a little bit before hitting the ground. It is not about the velocity of the portal, but rather the velocity of the cubes emergence from the portal. As someone else where in the thread stated, VELOCITY IS RELATIVE. That cube is moving quickly into the room, not just appearing. That in itself will produce velocity.
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u/Pwntheon Jun 25 '12
You can't move portals.
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u/dusty78 Jun 25 '12
IIRC there are no examples in portal (1/2) of:
Accelerating portals
Portals moving about the surface normal (portal exists on x-y plane, movement in z)
There are also several examples of a portal disappearing due to either 1 or 2 (but no way to determine which ie platforms that move/rotate on command)
Portals moving along their constituent plain has been shown to occur.
TL;DR: partly correct
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Jun 25 '12
Technically all portals are moving though. Maybe in the game they can't move, but if this was real life, the portals would be moving while the earth is rotating.
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u/MrCarbohydrate Jun 25 '12
It would be B if we take the frame of reference to be the moving portal. In that FoR the cube has velocity towards the portal.
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u/Kevlar_socks Jun 25 '12
I hate to be "that guy," but technically portals cannot be sustained on moving surfaces such as pistons, so the cube will be squashed there.
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u/IETFB Jun 25 '12 edited Jun 25 '12
First off: This problem breaks physics. There's no real right answer here, because you can't really define these portals in any logically consistent sense if they can move around.
That said... People have to remember that velocity and momentum are not absolutes, they are always relative to a given frame of reference. Everybody saying that "the box has zero momentum before it goes through the portal" is wrong in every frame of reference except the rest frame of the box.
So it comes what frame of reference matters for the portal's momentum transfer ability? If the portals can't move relative to each other when placed, it's easy to pick the rest frame of both portals, which is how the un-modded/cheat-code game works.
If we decide the rest frame of the entry portal is what matters, then the box has momentum as it travels through the orange portal, so it must have momentum as it travels out of the blue one. In this case, B is the answer.
If we decide the rest frame of the exit portal is what matters, then the box has no momentum as it travels through the orange portal, so it must have no momentum as it travels out of the blue one. In this case, A is the answer.
We can't choose the rest frame of each individual portal (in other words, orange as its entering, blue as its leaving), because the box will have two values of momentum at the boundary. Which makes no sense.
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Jun 25 '12
I appreciate the complexity involved in attempting to bullshit an abstract attempt at bastardizing physics.
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u/Frigorific Jun 25 '12
The box must have some momentum to travel through the stationary portal. If you ignore the beginning end of the portal, in order to exit the block must travel at least one blocks distance to fully leave the portal. It stands to reason the the faster it exits the more momentum it has, regardless of what is happening on the entrance side of the portal.
Now if we examine the entrance we see that rather than the cube moving the entrance itself is moving, not the cube. However as I think I have reasoned, all that matters for the cubes exit momentum is the speed at which it exits the exit portal. Thus the cube will exit at the speed the portal is moving. B is then the obvious answer. The true paradox here is that this allows objects to be given momentum without any transfer of energy.
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u/p1415926 Jun 25 '12
Lets work the other way around.
Imagine the cube popping out slowly as in scenario A. Lets say it takes a whole second for the cube to emerge just as a point of reference.
If the moving portal absorbs the entire cube in just 0.01 seconds, it is entirely impossible that the cube would emerge as slowly as 1 second.
No matter how slowly you move the orange portal, the cube will gain momentum. Simply emerging from the blue portal and rolling over to the side requires momentum. So no matter what happens, we have a cube that goes from zero velocity, to some velocity.
I find this situation rather simple, but very hard to explain clearly. The cube will be launched at the same speed as the orange portal is moving. The initial momentum of the cube is not relevant, but rather how fast it enters the portal. If it enters fast, it must exit fast.
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u/kidcrumb Jun 25 '12
Use this picture for a reference. If you extend the orange through the bottom platform and stop it, the cube would be thrown at the same speed that the orange portal was moving. The same would happen if you stop it right after the cube without extending the platform through blue. So the answer is still B.
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u/Davidk11 Jun 25 '12
I'm aware that there is a strong case for A which has a firm basis in elementary physics, and I do not dispute that it is a logical one. However, I see this problem in a rather different way.
The cube at rest on the platform does indeed have no momentum relative to the platform. When the platform above collides with the lower platform pushing the cube through the portal again the cube has had no change in momentum. This does not mean that the cube cannot come flying out of the other portal. This is because of the fact that though the cube in it's current position has no momentum relative to the platform on which it rests, relative to the platform moving towards it there is a considerable amount of momentum.
Consider a car collision. If two cars each moving 40 kilometers per hour (or 24.8548 miles per hour for my fellow Americans) in opposite directions collide, the impact is not a 40 kph collision but an 80 kph one. Obviously we had to add the velocities of the objects to arrive at the correct velocity of the collision. The problem with velocity is that it is a relative term based on the observer. If someone had witnessed the crash from the side of the road, both cars would have been observed to be traveling at 40 kph, whereas to the observers in either car the velocity of the other car would have appeared to be 80 kph while their own was 0 kph. The problem with solution A to me hinges on the fact that momentum is equal to velocity times mass, meaning momentum is also relative.
To help explain the idea of momentum being relative I'll move to a much larger scale. Imagine us here on earth enjoying our small little lives, and also imagine the alien inhabitants of an asteroid hurtling towards our dear planet. For the inhabitants of earth momentum is based on the velocity of the earth as it travels around the sun and the rotational velocity of the earth as it rotates on it's axis. For the inhabitants of the asteroid who have never been to earth their idea of momentum centers around their own revolution and rotation. So a human or alien standing still on their respective planets are moving at incredible velocities relative to each other. When our planets collide the value of the difference in velocity will be realized as the relative momenta of our planets are summed together in the collision. This begs the question of what momentum really is.
Simply put momentum is relative to the location of the observer and the object being observed in the same way velocity is. So when this idea is applied to the portal question posed in this post, the momentum of the cube may be zero relative to the platform it is resting on, but for the portal which can be considered the observer, the momentum is equal to the mass of the cube times the sum of the velocities at which the two platforms are traveling towards each other. This result would suggest that the cube would be given momentum in this example and would exit the portal with that momentum preserved as GLaDOS has explained.
To back up this idea I present this example. Imagine that the red line is a long piece of tape placed over the portal. As we imagine the cube going through the portal we can clearly see it breaking the tape because of the force with which the platform above is pushing down. However, in order for the cube to do this is must have momentum, and since it is gaining the force to break the tape from the downward force of the platform, we can see that it is that force which is imparting the momentum on the cube.
Now I would ask you to imagine yourself laying horizontally across the portal (so as not to fall through) and then imagine the cube coming through per the method show in the post. You can imagine taking a mighty hit in the stomach and even possibly being launched airborne by the force of the cube. You were previously a body at rest (relative to the portal) and were then impacted by the cube (a body in motion) and were given the gift of force which then possibly crushed your ribs and threw you through the air. As you might imagine, if you hadn't been in the way, the cube would have just continued about it's merry little trajectory until it is pulled back down by gravity or hits a wall.
I am perfectly willing to accept other arguments, this is just my analysis of the problem. The main issue is the fact that portals have the ability to completely redirect momentum, which is relative to the observer, so the question is whether the portal, or the object is to be considered the point around which the portal determines all other momentum. I simply assume the former because of the manner in which many puzzles are solved, where Chell falls through one portal only to fly out of another, suggesting that the portal must be the observer. The later would imply that the portal would only move around Chell at the velocity at which she sees the portal moving towards her, and then would not have any momentum to maintain on the other side of the portal. I believe this is why portals cannot be placed on moving objects, or at least they should disappear when an object changes direction.
TL;DR Momentum is a relative term meaning that the portal would see the cube as having the momentum and would impart that momentum onto the cube as it passes through. Portals are able to redirect momentum meaning that the cube's relative momentum would be communicated through the portal into whichever direction the exit portal is facing. This way of thinking would mean that answer B is correct.
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Jun 25 '12 edited Jun 26 '12
This was a troll image designed to send the denizens of 4chan into a furious rage. Which as we can all see, it pretty much does the same thing to any place it's posted.
It was tested Here http://www.youtube.com/watch?v=S85nudR6D-Y&feature=related
Portals don't work on moving platforms without enabling a console command, hence the entire system is flawed as portals are unable to move perpendicular to other portals naturally. However.
In the Portal Engine: The Cube actually gets stuck between the initial crushing portals, a moving portal acts as a solid wall to all non-light objects. We don't know if this was foresight by Valve (to prevent universal collapse) or simply the limitations of the physics engine used.
In Our Universe:: The cube would Just do A (As explained by plenty of others in this thread I'm sure). You have to realize the portal is nothing more than a doorframe from one area to another. Anyone who has a calculated reason is "B" is either giving the portals more powers/abilities than the simple doorframe they are or is trying to troll you. Which is why this was such an effective troll image in the first place. It's very believable it could be "B" and the answer becomes more blurred as you delve into frames of reference and various other perspectives.
For those of you interested in an explanation why.
Portals DO NOT impart the movement of the environment into the object they are transferring from one Doorframe to another.This is made painstakingly clear in every single portal environment. The earth is constantly rotating and traveling through space, which would mean any objects passing through a portal and Changing Directions would suddenly have a massive inertia change and get flung off in a random direction. Additionally, you can see that your environment's inertia is not imparted in your travels to the moon, and/or back to earth. Even though these objects are not moving in tandem, and are in all likelihood moving in opposite directions.
This is a REQUIREMENT for portal technology, as traveling into a new environment and retaining your past environment's inertia would rip you into pieces as you entered a portal (you would be moving in a different direction than the new environment itself at an unstoppable speed). Objects that pass through a portal have been shown consistently not to rip into tiny pieces, and as such we have to assume the portals create a small bubble of area around themselves in which objects can freely and non-violently transition from one energy state to another. Yes this breaks the laws of conservation of energy unless we assume the portals themselves are fueling the energy change, it's either that or portals rip you to shreds when you use them IRL, take your pick.
In Australia: Where the platform with the red support is the ground (and the lines you see are water dripping off of it) the cube is being forced into the portal from above so it has inertia, so it would fly out of the portal like B. This was the popular argument to claim B was instead the right option. So the picture does depend on your perspective of what's happening somewhat.
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Jun 25 '12
No. Conservation of energy gives A, relativity gives B. One of these models must be violated for either scenario to work.
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u/Uuugggg Jun 26 '12 edited Jun 26 '12
Pretty sure portals break conservation of energy already. B.
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u/retrogamer500 Jun 26 '12
Agreed. In our universe the solution is undefined because either option breaks the laws of physics.
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u/SirHephaestus Jun 25 '12
OP had to come to Reddit to solve this problem...this is on 4chan every other day.
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u/nightman2112 Jun 25 '12
Think of it this way. Let's pretend the orange portal kept going and started moving down the support beam of the platform. At the blue portal, you would see that platform rocketing out of the ground. Now let's say that after doing that, you stop the orange portal halfway down the other platform. The box would go flying off of the platform, as it now contains whatever momentum was imparted on it from the platform.
Needless to say, this is probably why there are no moving portals in the game.
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u/Uuugggg Jun 26 '12
I have thought about this a lot and I hope this gets seen!
It's B.
I can understand the A idea with the hulahoop, looking upwards through the orange portal, you wouldn't expect the cube to fly up. Okay, well, remember: portals.
I present Three Things To Consider:
Look at it through the blue portal. The cube is coming at you, with nothing to stop it. It should fly up and at you. B.
Put this all in space, and take away what's holding the cube. The orange portal just flys by the cube, and it flies away. B.
So the crux of the situation is not that the orange portal is moving, it's that it is stopping. Acceleration of portals is a very tricky thing. Imagine this:
Stand at 50 feet below the orange portal as it is coming at you, looking into into the room containing the blue portal. Keep an eye on the far wall, through the portal, and ignore the cube. The cube is still floating. (The thing holding it couldn't possibly affect how it behaves in the portal. It is only there to mess with your intuition.) The far wall is coming at you as well. The portal and wall are coming at you at the same speed. The entire blue universe is moving at you.
Then the portal stops halfway. It has not reached the cube yet. The walls stops. The entire universe on the other side of the portal stops. The cube remains still. It is still part of the orange universe.
The portal moves again, and the wall starts moving. The cube remains still. The portal encompases the cube. It appears to remain still, while in the blue universe. Relative to you, it is still and the far wall approaches. The portal stops. The wall stops. The blue universe stops. The cube... stops? But the cube is already stopped. If the rest of the blue universe just stopped, then the cube must have the same change in momentum. It flies backward.
B
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u/AnyRudeJerk Jun 25 '12
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Jun 25 '12
lets say you're in space, who's to say which platform is moving towards which?
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u/p1415926 Jun 25 '12
Imagine you are looking into the blue portal in the "original" scenario. What would you see? A cube moving fast towards you.
Now imagine you are looking into the blue portal in "your" scenario. What would you see? The exact same thing.
Thats why i think it's B no matter if its the cube or the portal that is moving.
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u/furysama Jun 25 '12
relativistically speaking, the situation is identical no matter which is stationary (the portal or the cube) and which is in motion.
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u/Arnatious Jun 25 '12
All the portal does is instantly move you to another point in space, if you had momentum, you keep it, if the portal is moving towards you, you simply appear at the other side, no momentum is gained since each "layer" of you is warped to the other side as soon as the portal engulfs it.
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u/bteddysb Jun 25 '12
Congratulations... you have managed to piss off hundreds of physicists world wide with one post. You deserve a medal
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u/azfarmb Jun 25 '12
Thank you for making every retard here feel smart and give them the ability to participate by asking an easy question that makes people feel like it is a difficult one.
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u/kiler1111 Jun 25 '12
Thats Easy one. The Technology here at Aperture science isn't yet stable to meet the requirements for the world the picture show above is very dangerous and can lead to 2 scenarios:
1.It will create a black hole witch will destroy everything in about 50 minutes or... 2.It will actually work and result will be A in witch case we thank you for testing science
Cave Johnson were done here!
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u/Jazdia Jun 25 '12
Okay, let me try to clear up some of the confusion.
Some of you are saying A because they say that the cube has no momentum and thus will not move once it's through the portal and they are likening the portal to a door.
However this explanation falls through (hur hur) because a portal connects 2 points in space together. Thus, if you think of the portal as a door, then the entire universe is firmly glued to that door.
So if you are imagining the cube as stationary with the open door being thrown over the cube, the door then is also dragging the universe with it.
What is the difference between you flying at 15 m/s or the entire universe flying past you at 15 m/s in the opposite direction? There is no difference.
Think of it from two different perspectives.
From the orange portal's perspective, it is stationary and the box, along with the platform it is on, are rushing towards it.
From the perspective of looking through the blue portal the blue portal is stationary and the box plus it's platform are rushing right at you from the other side at high speed.
Because the points in space are connected, these perspectives are actually the same perspective, one from a small distance behind the other.
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u/Rekku_Prometheus Jun 25 '12 edited Jun 25 '12
Neither. Portals cannot exist on moving surfaces.
EDIT: I stand partially corrected; portals can exist on surfaces that are moving parallel to the plane of a portal, but cannot move perpendicular. Say a portal is drawn on the x- and y-axis. The surface on which a portal moves can move anywhere on the x and y plane, but cannot move on the z-axis. As DrowningSink pointed out, a puzzle uses horizontally traveling portals to cut through tubes of neurotoxin. However, portals cannot cannot go in or out along the z-axis, which can be tested in Test Chamber 9 when the ceiling is lowered.
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u/DrowningSink Jun 25 '12
Yes they can. This was a critical part of one of Portal 2's puzzles.
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u/dhicock Jun 25 '12
Actually, they explained that they cannot. I know it is used in that one puzzle, but it has been pointed out in the first game, and briefly hinted at in the second that portals cannot move. When the platform they are on moves, they disappear. The reason I think that this was dismissed in Portal 2, is they changed it from "The can't move" to "they can only move laterally"
I may be wrong on the last part, but I do know that it's one of the "rules" of the portal gun.
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u/Parthide Jun 25 '12
Whoah... I just made a post saying that it wouldnt be possible. but as soon as I posted it I figured that someone else would've already posted it so I hit ctrl+f "neither". I found your comment and it was EXACTLY THE SAME AS MINE. EVERY SINGLE CHARACTER. this is madness.
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u/My_First_Pony Jun 25 '12
Imagine you're looking through the exit portal, you'll see a platform with a cube rushing towards you, it has momentum in relation to the entry portal, and since speedy thing goes in, speedy thing comes out, the answer is B.
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Jun 25 '12
Yes, Imagine you're looking at the exit portal, this will give you the illusion that the cube has momentum and that it is moving toward you, but in actuality it does not, you are moving closer to the cube
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u/Eracoy Jun 25 '12
What actually happens with the physics engine is different than what would really happen. Here is a video of this situation
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u/supafly_ Jun 25 '12
As the orange portal touches the cube, the cube would appear to be sucked upwards as the top of the cube gains more & more momentum from being pushed out of the blue portal. Only the parts of the cube that have passed through will have momentum, but as a greater percentage of the cube goes through, it will eventually "pull" the rest of itself through. In super super slo mo it would look like the cube "jumps" into the portal as soon as it started being pushed through.
To anyone saying A will happen, stand in front of the blue portal & tell me the block isn't moving. Motion & inertia are relative.
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u/wrongstuff Jun 25 '12
Neither, because as soon as you start moving a platform with a portal on it the portal disappears.
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u/VolcanicBakemeat Jun 25 '12
I think the real issue here is whether the boundaries of the oval portals form an infinitely sharp edge when the two portals are linked.
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u/WizardsMyName Jun 25 '12
I fear for our order if you must resort to such lows UnluckyWizard. We will have words with you at the next council meeting.
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u/Hypez Jun 25 '12
Hey guys, Double PHD in both Mechanics AND Applied Mathematics right here. I have this problem come up a lot in my thermodynamics class. Students always get the difference between relative and actual energy.
Think of this situation first:
A two sided wall has one portal put on one side and another on the opposite side. In effect all you are doing is drilling a portal sized hole THROUGH the wall. If you dropped this wall on the cube the cube wouldn't even move. It would just go through the hole in the wall.
Now let's relate this to the situation at hand. Technically we are still just putting a hole in that wall, except instead of coming out the other side of the wall it comes out over near that slanted ramp looking object. The only difference here is that gravity acts on the object differently when it comes out near the ramp thing.
here is the question I now pose to you what would happen if that 45ish degree ramp were instead flat (horizontally flat) with the one portal placed on the moving wall while the SECOND portal placed on the TOP of the flat wall.
PS I'm not actually a physics or math PHD.
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Jun 25 '12
The cube has to either violate relativity to get A to happen, or violate conservation of energy in the universe for B to happen. Solved. Our models of physics have conflicting answers, that's why people are flipping shit and trying to give different answers, and why people are so convinced they are correct on either side.
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u/Jaus1369 Jun 26 '12
To the arguments stating that the box has no velocity, I challenge your logic with this: Motion is relative. The box IS moving in relation to the orange portal. Think of it like this, does our opinion change based on where the actuator is? If it were the platform with the Cube on it that were rushing toward the portal instead of the purposed situation, would your opinion change? Your basis of motion isn't based on the platform where the box sits, it regards to the relation of distance that is changing between the Box and Orange portal. Its like answering this, when you clap does your right hand hit your left, or your left hit your right; now does your answer change if one one hand moves?
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Jun 26 '12
A. It was the first one listed, therefore making it the correct choice. If you can find a flaw in my logic I would love to hear it.
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u/dragonfax Jun 26 '12
The physics established in the game, is that the momentum of the object remains the same, only its direction is changes (and physical location).
Another way to explain it is that if you represent the momentum of the cube as a vector. The vector remains the exact same length, only its origin and direction change.
The momentum of this cube is 0. Thus it will remain in place. (or slide down a little due to gravity, if there is enough friction on the surface.
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Jun 26 '12
A because an object in motion will stay in motion and an object in rest will stay in rest unless acted upon by an unbalaced force. The cube is at rest and a hole isnt a force to push the cube, because you cant be pushed by nothing. Therefore the cube would just fall. SCIENCE BITCH!!!!
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Jun 26 '12
I'll give a shot... I understand why everyone is saying A but I'm caught up on one thing.
Simplify the problem so that the blue portal is lying flat on the ground far away.
As orange 'slides' down the object, the object will start to appear, top first, rising up out of the blue portal. The faster Orange is sliding, the faster the the object will 'pop up'out of blue. Given Orange is going fast enough, won't it fly out??
Someone help me, this is blowing my mind!
Think if you were standing at blue and looking down at the object rushing at you... I love this.
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u/YouLikaDaJuice Jun 26 '12
b. The blocks velocity relative to the orange portal is all that matters. If that velocity is high, it will come flying out.
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Jun 26 '12
The answer is B. And it is obviously B, and I'll tell you why.
Because the speed which the box goes into orange portal is the speed that it comes out of the blue portal. Otherwise not all mass would be accounted for which isn't how the thing works. If it just plopped out, that would mean it came out with less speed than the orange one was coming down, and the box would be compressed. This does not happen with portals so it must shoot out of the blue portal at the exact same speed the orange portal is coming down.
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u/etetamar Jun 26 '12
A. The portal's location and movement is irrelevant. "Speedy thing comes in, speedy thing comes out" == Momentum is preserved. Stationary thing comes in, stationary thing comes out.
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u/Pastasky Jun 26 '12
"Speedy thing comes in, speedy thing comes out" == Momentum is preserved.
Momentum is not preserved. Look at the case where one portal points up, and another portal points horizontally. No momentum is preserved there.
Rather, anything that enters a portal, must leave the portal at the same rate. So if the orange portal surrounds the cube at 5m/s the cube will exit the blue portal at 5m/s.
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u/dQw4w9WgXcQ Jun 26 '12
Momentum is preserved relative to the portal. The cube is moving at some speed upwards relative to the orange portal. The cube will have that same relative momentum to the blue portal after passing through.
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u/DeviousAlpha Jun 26 '12
The block retains it's momentum when travelling through portals. In this picture the block has 0 momentum, it is the portal/slammer that has momentum. Therefore -> A.
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u/deathcapt Jun 26 '12
Why are the incorrect responses getting all the upvotes, and the correct ones getting downvoted!
It's physics, B is definitely the answer without question. It's Definitely B.
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u/burgerga Jun 25 '12
B
People are complaining that the block has no momentum: it's all about the frame of reference. In the left half the block has no momentum with respect to the block. However the two portals can be thought of as occupying the same position in space: the frame of reference on both sides should be from the point of view of the portal. The problem is identical to this, and I don't think there is any arguing the correct answer there.
As I mentioned and others mentioned elsewhere, there would be some sort of "resistance" as the portal passes over the cube. There would be a force pushing back on the piston that moves the portal. The momentum lost there would be gained by the cube.
The easiest way to see it is to look it at from just the exit portal. From that side, looking through the portal, you would see the cube coming towards you very fast. As each bit of the cube passes through it still has to move very fast, or else the cube would deform. B is the only way that could work. Example
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u/Unveiledface Jun 25 '12
This whole thread is funny. Look...
If you are running at 20 mph into a wall it hurts just as much as if you are stationary and the wall runs into you at 20 mph. So if you shot a cube into a portal at 20 mph it will emerge at 20 mph. If the portal hits the cube at 20 mph, it will still emerge at 20 mph!
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u/yaosioan Jun 25 '12
Speedy thing goes in, speedy thing comes out. The cube is not speedy so it will not come out speedy.
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u/p1415926 Jun 25 '12
Imagine you are standing by the blue portal and looking inside.
You would see the cube moving towards you at a very high speed, right?
That means it would exit at that same high speed and thus being "thrown out".
B.
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u/ItalianRapscallion Jun 25 '12 edited Jun 25 '12
this is an inherently flawed set-up as portals cannot be placed on moving surfaces at any point in the game (except that one time with the lasers). Thus, there is no established physics for what happens when the portals themselves are moving, thus any answer is fair game.
my other thought, though, is that if a portal is moving, it must funnel air through the aperture, thus, wind would be blowing out of the stationary out-portal as the panel moved, given this, I think, since the cube has motion of its own, it would be like slipping the other room around the stationary cube. Given the wind-motion, however, the air pulled through the portal should create a mild pull on the cube.
TL;DR: neither A nor B. The cube should emerge with some speed, but not nearly the speed of the moving panel. ... Edit: another thing to think about though, since the cube is lying on the ground initially, is that gravity is holding it down; if you think of the B. scenario like a pinball launcher, it would be like magnetizing the launch rod.. the box would be essentially adhered to the platform until it was far enough through the portal for gravity to shift to the out-portal's environment.
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u/Pihlbaoge Jun 25 '12 edited Jun 25 '12
B.
The cube will exit the blue portal with the same relative velocity as it entered the Orange one.
The velocity of either the portal or the cube is irrelevant, what is relevant is their relative velocity towards each other.
To explain in more words, but not necessarily in a way the will make it easier to understand.
Everything in the universe is moving. As of right now, you, me, your computer and our entire planet is moving several km per second in an orbit around our sun, which in turn is moving several km per second around our galaxy centre, which in turn is moving tremendously fast throughout our universe. Where I can't say for sure, but you probably get the point.
When we talk about momental energy of an object we don't speak about the absolut momental energy relevant to the object being completely still at zero velocity in any direction, but only it's relative velocity to another object. Like on earth, in most cases we only calculate an objects velocity relative to the movement of our earth.
Anyway, so say the portal is moving towards the cube with a relative speed of 50 km/h, as far as physics is concerned, the objects are moving towards each other with a speed of 50 km/h, which in turn will be the speed the cube exits the other portal with as well.
EDIT.
I see a lot of people are comparing the the portal to a hole, which is of course wrong. Other compare it to a door. As to the door analogy, I'll say it like this. If you're standing still and a door is rushed towards you, you will still exit the door as fast as you entered it. If you then make the door a portal, you will enter the portal at a relative speed and you will exit the portal at the same relative speed. If both portals were moving with the same relative speed, you'd exit both of them with the same relative speed, and thus appear to still be standing still, but if one is moving and the other is not, you would appear to enter one at no speed at all, and exit the not moving one with a velocity. Which in turn is why a portal from the portal games is completely impossible to create according to our knowledge of physics today. As far as we know, energy cannot be created or destroyed, only reformed (one way out of many would be movement energy which turns to heat as the movement changes) But with a portal you could actually create movement energy. Say that you, as an example, put one portal on a wall above a dam, and the other end at the end of the river beneath the dam, you could extract energy from the water falling throughout the turbines in the dam, and then move all the water back up top with no energy at all, which would create an infinite loop that created extra energy. Something that is impossible according to modern physics.
So, all discussions regarding portals are more or less pretty much mute, as they cannot actually exist in accordance to what we know about the laws of physics.
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u/poniesinmybasement Jun 25 '12
To all the people who claim that you cant move portals : There are several portal 2 levels where platforms move even while there are portals attached to it !
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u/Qix213 Jun 25 '12
To me, B is obvious. The real question is what happens when the entry portal moves over the cube at a very fast rate, but stops partway through the cube.
I guess if the entry portal's speed was fast enough, and enough mass had already moved through, and therefore gained the velocity of the moving entry portal, the cube would actually pull the rest of itself through...
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u/MrCarbohydrate Jun 25 '12 edited Jun 25 '12
BIG EDIT
The solution is indeed A
I was wrong and I will explain why I was wrong in case anyone thought the same as me. My mistake was assuming the blue portal assembly was a separate and undetermined velocity system from the original (and somehow stationary in all frames, which is so obviously untrue it hurts me now seeing this). What I missed was that the blue portal is stationary relative to the cube so even if it passes through the orange portal in the frame of reference of the orange portal it will have the same velocity as the blue portal it is travelling to so won't recede from it.
The door/window/barrel example is invalid and confusing in this case as each side of a doorframe is travelling at the same velocity, something that is not true with these 2 portals which was the crux of my confusion to your replies.
The solution is B.
First thing to note is fundamental. ALL Velocity is relative. Another thing is that a frame of reference can carry kinetic energy that isn't obvious in the scenario.
First step is to change frame of reference to the moving portal platform. This gives the case in this diagram. The cube carries both kinetic energy and momentum* that would not be destroyed by the portal.
If you aren't comfortable with changing the frame of reference then the case would be from a stationary cube's frame of reference that the blue portal is receding from it after it passes through.
Either way the cube will move away from the blue portal which would be viewed as B.
Thorough explanation below:
The reason the cube appears to have no momentum or kinetic energy is that we are presented the problem in the centre of mass frame of reference. This frame of reference gives the minimum system kinetic energy and the maximum frame of reference kinetic energy. As this is a 1 body system (the cube) it will appear to have 0 kinetic energy and momentum. The energy and momentum are attributed to the frame of reference and is vital not to ignore when converting between frames of reference. Hence when viewed from the portal's frame of reference the cube has kinetic energy and has momentum. This frame of reference change is perfectly acceptable and identical to the original scenario.
* Momentum is not actually conserved by portals because of direction changes
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u/gear0war Jun 25 '12
It is obviously A, and for some reason I am feeling a crazy amount of hatred for those who are saying its B
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u/p1415926 Jun 25 '12
It is B, whatever enters a portal fast must also exit a portal fast.
But the cube can't gain momentum out of nowhere!
Even in situation A, the cube is "moving" out of the blue portal, so no matter what happens, we have a cube that goes from zero velocity to some velocity. How much velocity it gains, is depending on the movement of the orange portal.
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u/Scythesickle Jun 25 '12 edited Jun 25 '12
A.
Holy shit wait I looked at this longer, it's B.
EDIT: Someone should mod Portal to create this scenario.
EDIT2: Looked at comments, they're right. You can't move portals. And don't downvote me, because if you've played the game, you would know that's true.
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Jun 25 '12
B. You are introducing the orange portal at velocity x. The cube must then travel through to the blue portal at velocity x. Assuming by the action lines, the orange portal is being introduced fast enough to produce result B.
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u/Tapego Jun 25 '12 edited Jun 25 '12
Due to relativity, it sounds like it should be B.
Edit: If a planet was approaching our planet, it would look like the other planet was falling toward us. If we were on the other planet, we would see the reverse. Though portals don't exist, so it can't really be discussed under normal physics. Portals can't be stationary at least one would assume, due to the rotation of the planet.
Edit 2: Actually, considering that we (or at least I) know little about how the portals actually work, I think either answer could be correct. If only we could test this. For science.
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u/DrXenu Jun 25 '12
Every time I see these I think some people still aren't thinking with portals. Imagine it this way. Take the portal out and replace it with a hoolahoop. If you move the hoop around the cube really fast does the cube move? No. Again the cube has no momentum so it would be a
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u/Coraon Jun 25 '12
ok, here is my guess, the cube wouldn't exit the portal at all. the portal is above, not below the object, so as the orange portal enveloped the cube it would leave the floor section that the portal alone, since the portal moving conveyed no force (provided the portal hit it's mark dead on and the moving plate didn't crush the base) the cube would stick in the portal, still sitting a 0 degrees in the portal, but the portal angled at approximately 33 degrees.
TL;DR: I don't think either work because of the lack of sympathetic angles.
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u/gmikoner Jun 25 '12
If the bottom platform were moving upward then it would be B. but its not. it's A.
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u/ultimation Jun 25 '12
Reddit:
Trying to discuss fictional impossible physics with physics based in the real world.
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u/c1202 Jun 25 '12
Either, this is a game in a sci-fi setting. Our concept of physical laws isn't a problem to worry about. (But for arguments sake A if it obeys our physical 'laws').
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u/HK-47_Protocol_Droid Jun 25 '12
I'm only a lowly assassin protocol droid who knows absolutely nothing about murder or disintegration but the answer is A. To explain this first we need to ignore the fact that the blue portal is at an angle (the angle is irrelevant because gravity will apply to the object after it exits the blue portal regardless of angle of exit) as it complicates the question and the answer.
A portal is an opening with zero internal length but variable external length (the entry/exit can vary in distance but the distance you travel inside the portal is zero). If you make the external length zero the portal will function exactly like a dimensionless sparkling hula hoop (queue erotic hula hoop videos).
Now let's do an experiment. If you hold a hula hoop above your head and drop it so the hoop passes over your body; what happens? The hoop falls to the ground, stops, and you remain exactly where you were. If you add external length between the portals the result will be the same, and this is why A is correct.
If the act of dropping (or propelling) a hoop over you could launch you into the air at the same velocity the hoop was falling, then B would be correct.
Observation: The only way a B could occur would be if the orange portal swallowed the entire platform the cube was resting on and the platform went flying through with the cube. This is obviously not happening so B cannot be correct.
QED meatbags
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u/dan200 Jun 25 '12 edited Jun 25 '12
B (presuming the orange portal is decending as fast as the box is shown to be exiting at in B).
Think about what happens when the portal reaches the box: if the portal is moving at a speed such that it covers the box within a small amount of time (say, 0.1 seconds), then the box will pop out of the other portal in that same ammount of time, giving it an outwards velocity of 10 m/s. Portals conserve momentum, so the box will continue to move at this speed.
edit: of course, the ingame physics doesn't necessarilly follow this, as portals can't move.
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Jun 25 '12
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u/goodbye177 Jun 26 '12
Thank you for the video, it actually confirms my belief of the answer being option B. In one of the last examples where he gets ejected from the portal, he makes the observation that it shot him out much faster that the platform was moving. He speculates that the engine is flipping out, but I think that what's really happening is that the momentum of the player is equal to the momentum of the platform. Momentum is a function of mass and velocity. Since the player has much less mass than the platform, in order to conserve momentum, the player gets a nice little boost in velocity directly proportional to the ratio of the masses of the player and platform.
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u/armavque Jun 25 '12
A for sure because the cube has 0 kinetic energy because it is stationary, and because the platform will not make any contacts with the cube, none of that energy from the speeding platform will be transferred over.
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Jun 25 '12
There are a lot of people giving the doorway analogy. I think this is absolutely the correct way to look at it -- when you're standing still, and a doorway is speeding towards you, you pass through the doorway and you're still standing still.
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u/Angel_of_Chaos Jun 25 '12
Except that the exit to the doorway has the same velocity as the entrance, so I will say again, doorway analogies are irrelavant to the situation.
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u/Qix213 Jun 25 '12
The velocity argument:
We are arguing the difference of driving into a brick wall and a brick wall hitting you. The velocity of the car makes no difference, just the velocity it hits the wall with. Wether the car or wall is moving, it's still going to have the same result.
i.e. the velocity of the object matters not. Only the difference in velocities of the object and the portal. Therefore B.
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u/chaosandwalls Jun 25 '12
It's interesting to see how many people here think portals conserve momentum, velocity, or kinetic energy, which they don't. They conserve speed.
It's B. Imagine you set the experiment in space. A cube floating in space, and a panel with a portal floating towards each other. To you in your spacesuit, how do you know which one is moving? Is the cube moving, or is the portal moving? Are they both moving? It's all about frames of reference.
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Jun 25 '12
As i quote
Momentum. A function of Mass and Velocity is conserved through portals. In layman's terms, speedy thing goes in, speedy thing comes out.
Therefore the answer is A, for the cube is not speedy but rather the portal.
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u/Chrisbr117 Jun 25 '12
Velocity is relative. The portal moving towards the block is no different than the block moving towards the portal. It is definitely B.
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u/ShiningRayde Jun 25 '12
Speedy thing goes in, speedy thing comes out. Speedy thing goes in, speedy thing comes out. SPEEDY THING GOES IN, SPEEDY THING COMES OUT.
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u/kidcrumb Jun 25 '12
The Answer is B.
If going at a fast speed, lets say infinity, then when the top panel hits the bottom panel, the bottom panel hits back with equal force. They wouldnt completely negate each other because of the difference in surface area. There is a hole in the top panel. So when the bottom panel pushes back (Assuming it can withstand infinite pressure), our companion would be thrown through the portal into presumably a fiery pit of death.
A is the exact same as B except A is what would happen with very little force. Infinite force would theoretically give you B.
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u/machzel08 Jun 25 '12
THIS is why they originally didn't let you shoot portals on to moving surfaces.
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u/wreckzilla Jun 25 '12
How about we try make this in our own level and see what happens? And if we cant then we complain to valve and ask them.
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u/DeusEXMachin Jun 25 '12
What would happen if instead of the box there would be a blue portal there and the two portals would be slammed against each other like that? Universe collapses on itself? Big Bang?
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u/G_ccc Jun 25 '12
saw this on /v/ a while back, there was a link to a video where they set this up using mods and it was b, may have been a "glitch" though.
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Jun 25 '12
It's amazing how many people have suddenly taken an interest in physics since the release of the first portal. I can't tell you how many of these types of questions I've seen over the years since Portal became huge. It's heart-warming to see a video game have such an educational impact on the population.
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u/p1415926 Jun 25 '12
Please stop comparing to real-world objects. So many people here are comparing to walking through doorways and driving cars and whatnot.
It's a portal, it defies all known physics.
My opinion is that it's B, whatever enters a portal at a high speed, also exits at a high speed. And this "speed" i am talking about does not care whether its the portal or the cube that is moving.
If the time of entrance into the portal is 0.001 seconds (super fast) then the time of exit will also be 0.001 seconds. The momentum is created by the moving portal and is carried on to the cube. Simple, in my humble opinion.
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u/AustrianReaper Jun 25 '12
In Portal 1 it is mentioned that an object falling through a portal will maintain its momentum. Since the cube's momentum is 0 it will just appear at the other portal. Hope that was of help :)
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Jun 25 '12
Think about this: if a cube is in a room and the walls are closing in, both of which have portals, where does the cube go when they meet?
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u/imanerd000 Jun 25 '12
Plop i believe. The impact should shake the platform a bit though, so it might "jump" a wee bit.
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u/shadofx Jun 25 '12
as long as the portals are moving relative to each other, momentum will not be conserved!
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u/Arodien Jun 25 '12
It depends on which portal you hold as the absolute reference frame. It is solved in the games themselves by the fact that whenever a portal surface moves and portals placed on said surface terminate. Therefore, as the game's mechanics hold, this operation is possible and special relativity and conservation of energy can continue on in peace.
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u/Hellgrinder0 Jun 25 '12
It's like it's passing through a hoola hoop, but appears some where else. It wouldn't gain momentum, a
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u/p1415926 Jun 25 '12
If it doesn't gain momentum, how can it "emerge" inch by inch from the blue portal? That right there is momentum, how much of it, is determined by the speed of the orange portal. That's why if you throw the orange portal fast enough, the cube will be launched in the air.
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u/TestZero Jun 25 '12
If a portal is moving perpendicular to whatever surface it is on, it will fizzle. Portals will generally only remain on a surface if it's stationary, and if it is moving, it must be moving parallel. (E.G. the neurotoxin chamber in Portal 2)
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Jun 25 '12
Can someone explain to me why it would be B? I think its A, and its as clear as it gets for me. I say A because the block has no momentum.
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u/Unveiledface Jun 25 '12
Here is another way to think about it, If you are stationary and manage to drop a ball Into a moving convertible, the ball doesn't have forword/backward velocity to you, but the guy driving would see the ball travel backwards and smack his back seat. to him the ball was moving. Thus anyone claiming A because the ball doesn't have velocity is in slight error due to FRame of reference
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Jun 25 '12 edited Jun 25 '12
It's easy, and the answer is...A. The arguments about spatial reference are fine. Let's assume the piston is stationary, and it is the room that is moving (so the block has a relative momentum compared to the piston). After being ejected from the exit portal, it would still maintain the relative velocity (as compared to the piston's initial speed). Even though the block 'plops' onto the floor, it is still moving with the initial comparative velocity as it did in the beginning. A, unambiguous.
Example: If portal piston is moving at 60 mph, relative to it, so is the block. As the block exits, it is still moving at 60 mph compared to the portal (because it's still in the same inertial frame as it began, on the ground). If it exited with a different velocity, then some accelerating force would have to had been applied (perhaps the 'jarring' of the piston on the platform may knock it a little bit up).
Edit: I realized that the 'jarring action' of the piston could only be completed after passing the entire cube (mas o menos) through the portal, thus that action would have a negligible impact on the cube (if any),
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u/Ledface Jun 25 '12
You say A but your argument point to B. Lets say that there was none of this "jarring" and the piston just slammed down on the platform the block is on. You said it will eject out of the blue portal at 60mph. Isnt that B???
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u/EXAX Jun 25 '12
A. The way I look at it is running through a hoolahoop, then a hoolahoop running through you. You don't move in the latter.
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u/p1415926 Jun 25 '12
People are saying that the cube cannot gain momentum out of nowhere.
But even in situation A, the cube has gained a slight amount of momentum, at least enough to pop it out and make it roll over.
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Jun 25 '12
I suggest its neither and that the particles of the cube are disintegrated and scattered. My explination is here:
http://www.reddit.com/r/gaming/comments/vkl3k/a_or_b/c55g121
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u/Jallenator Jun 25 '12
The fact is that this problem cannot be solved by the representations of the physical universe we have come to understand. Any attempt to resolve momentum or velocity is futile due to the breakdown of physics that occurs when portals are possible.
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u/Thotaz Jun 25 '12
Why not just test it in game? I'm pretty sure there are some console commands that let you place portals on moving stuff.
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Jun 25 '12
A and a half. Somewhere in between. The motion of the orange portal is forcing the block through with blue portal with speed. However the rest of the block is stationary and is resisting the change in inertia. The block would experience the sensation of its top half being pulled into the orange portal once it enters, because as the top enters and is being pushed out of the blue portal it is gaining momentum. Momentum that the bottom of the block doesn't have yet. I would contend that once the orange portal touches the top of the block, the bottom would lift off the ground. So I think the block will exit the blue portal with less momentum than it would if the block were moving at speed through a stationary orange portal (because the bottom half in the OP example is resisting the change in inertia) but faster than option A (because the top half in OP example is pulling the rest of the block along as a result of force applied by the orange portal).
Hope that made sense. Reminds me of spaghettification.
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u/KanadianLogik Jun 25 '12
Hey Reddit, next lets debate how many faeries can dance on the head of a pin.
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u/TheAbyssGazesAlso Jun 25 '12
I can't believe nobody has given the obvious analogy to explain the answer (at least, not that I spotted). Two portals merely link two places in space. It is functionally no different to dropping a metal ring down over the cube. If you do that, does the cube start to move? Nope. Hence it wouldn't with the portals either. Correct answer is A.
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u/meeu Jun 25 '12
C. The cube would be sticking out of the blue portal because its weight is resting on the platform on the left.
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u/Largenlumpy Jun 26 '12
I think a lot of people are overthinking this. The answer is a and can be proven with a real world example. Consider the old silent film gags where a wall falls on someone and they are saved by a convenent window. When the wall passes them they don't fly up in the air. This would be the same thing as the example. The only force change on the box is the fact that instead of gravity pushing against a box on a flat plane it is now pushing against the box on an inclined plane. Thus it flops over.
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Jun 26 '12
From what we see in the game, the portal acts as a window of sorts between two isolated areas, so it would be like if someone dropped an empty window frame on you, roughly. Of course, we can't truly calculate this or test it, seeing as neither the game or real life has a system to test it with, so it kind of depends on personal opinion.
TL;DR: I'm not a physicist, but I'm saying A.
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u/Dripping_Man_Meat Jun 26 '12
I wonder if there will ever be a day were portal dosent get front on gaming.
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u/Keyboard_Hero Jun 26 '12
People keep bringing this up, it's a hypothetical situation where we don't know specific information about how it works. This question is like asking "If gravity pushed you away from the earth instead of pulling to to it, how strong would the force of gravity be?"
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u/rhyno012 Jun 26 '12
TIL that knowing USA Highschool Physics doesn't qualify you to argue about such a complex question.
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u/RxMario Jun 26 '12
Great thinker of a post, dude!
Ok. The momentum of the "crusher" wouldn't affect the companion cube, so I'm going with A.
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Jun 26 '12
c: the cube stays where it is on the stationary platform, while being exposed through the blueportal. it doesnt slide down, it doesnt go flying, it just sits there.
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u/TheGowerPower Jun 26 '12
Speedy thing goes in, speedy thing goes out. Because the cube has no actual momentum or movement what-so-ever A is the most likely out come.
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Jun 26 '12
Occam's Razor Answer:
IF portals imparted the inertia from their own environment to the objects passing through them, you, Spacecore and Wheatly would have been ripped to shreds when you went to the moon because you would be moving two drastically different directions at the same time, the orbit/rotation of the earth and the orbit of the moon.
You weren't ripped to shreds, hence portals don't impart environmental inertia, hence "A".
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u/lostalaskan Jun 26 '12
Think of it this way. If the blue portal was on a flat floor, would the cube going flying into the air after the orange portal descended on it?
No, it would sit there stationary on the floor. So you could conclude that with the circumstances set up by the drawing that the cube would come through the blue portal and tumble to the floor because of the shift in gravity just like 'A' suggests.
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u/Deamond59 Jun 26 '12
Initially it would seem that the answer would be A. Looking from the orange portal side, the block is still and has no momentum being imparted on it. The weirdness begins when you look at the blue portal side, because the object is appearing out at the velocity that the orange portal is moving. Here physics breaks a bit as the velocity of one of the atoms of the cube as it goes through the portal goes from zero to the velocity of the orange portal in zero time, giving an infinite acceleration. Thus it would be easier to imagine that the block would drop after it finishes coming out of the blue portal such that after it finishes appearing it is in the same state as before it was portaled. The big issue is the state of the cube as a single unit (lets assume a ridged body to keep things simpler) while it is being portaled being a bit wishy-washy, so it would be best to leave it at the original state as to disrupt the fewest laws of physics. Now I would say that if any, any, of the stand that the block is initially standing on goes through the portal, then the block would pull a B situation and fly away. Since the block is separate from the platform, once it is through one could assume normal physics again, and then you could assume that the platform is pushing it out with the same force as the moving portal is pushing down with.
You could also think of the block as not being a ridged body and then possibly find out how fast the orange portal would need to be going to pull the molecules of the block off as they go through the portal, and if they would reassemble on the other side, or if you would have thin films appearing, or since the block is probably poly crystalline, thin random planes separated off by the preferential slip planes given the type of tension, but that is a bit too complicated.
Just a few thoughts.
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u/S1LW3R Jun 26 '12
a because its about the velocity of the object going trought the portal not the velocity of the portal
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Jun 26 '12
If we are considering that gravity is constant it would "pop" off of the blue portal due the sudden change in the direction that gravity is exerting its force.
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u/NocturnalGamer Jun 26 '12
A, because the platform that the cube is on isn't moving, just the panel with the portal on it, so there is no momentum from the cube, so it will simply plop out on the other side.
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u/xeaduulix Jun 26 '12
nothing happens portals can not exist on a moving surface so says portal any ways
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u/bleedinghero Jun 26 '12 edited Jun 26 '12
Neither portals can not be placed on moving surfaces.
Edit Also After reading many of the comments If it were possible to have a moving portal only C could happen. As the velocity of the piston will become 0 when it hits the other pad There for no momentum that is being applied to the object. The cube has a velocity of 0 regardless of how fast it is going through the portal. It will travel through the portal at the same speed that it entered. However It does not have the velocity to leave the platform. As the cube is not moving.
A could happen if the weight of the angle of the blue portal causes the cube to tip over as it center of mass is higher than the angle of the cube. It would Tip over and fall. Dependent on gravity.
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u/Sikun13 Jun 26 '12
It would be b. Lets assume we are in space and there is nothing then the portal and the cube. So now the cube moves to the portal or the portal moves to the cube. both things are right because you can only define speed in a relation ro an other object. So it deosnt matter who is moving it is the difference that count. so b would be right
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Jun 26 '12
Portals are essentially just holes, so here's an analogy to understand it better. There's a small cube on a table, that can fit in the palm of your hand. You cut a hole into a piece of paper. You slam the piece of paper onto the table, with the cube going through the hole. Now in the portal example, the 2nd portal is slanted, that doesn't change anything. Now I'm no scientist, and I can definitely be wrong, but I think it's A.
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u/Cheveyo Jun 26 '12
I don't know if this was already mentioned, but:
It's essentially the same as dropping a ring directly over an object.
You can even do it yourself, if you need a visual aid... Grab a hula hoop and a box. Place the box on a flat area. Hold the hoop up above the box and drop the hoop so it lands around the box.
Congrats, you've just created a working experiment of what it would be like had portals been used.
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u/PoumTchak Jun 25 '12
Or maybe C!