Memes

B since all movement is relative.

This was a triumph.

Portal would fail due to being placed on moving object

It needs to be 2. Otherwise all the people will materialize inside eachother. In fact, everyone will be deposited onto the 2-dimensional pane of the blue portal itself, like an infinitely thing coat of paint, absolutely smearing them.

Think about it. As your fingertips enter the orange portal, they materialize at the entrance of the blue portal. Then your wrist enters the orange portal, where does it materialize at the blue portal?

• If your fingers shift to make room, then that has imparted momentum and it's option B.
• If you continue to materialize on the other side of the portal like a mirror image, then for all intents and purposes the blue portal is also moving at the same speed as the orange portal, even if orange ring appears still.
• If your fingertips don't have momentum and your wrist materializes at the portal, then your wrist is occupying the same space as your fingertips. Congratulations, you're now a paste.

For whatever reason I feel more willing to break conservation of momentum than I am to

I think it has to be A. You figure that if it were B, the people on the track would suddenly be traveling at a high velocity, but the train's velocity wouldn't be impacted at all, since there was no impact between the train and the people. Wouldn't this mean that the portal had created energy, which is impossible?

Conservation of momentum says B I would think. From the protal's reference frame, the people are moving fast toward it.

Speedy thing goes in, speedy thing comes out

E: I was just quoting GladOS..... Not really thinking about the actual physics!

B. Since there is relative velocity between the orange portal and the target, the momentum is conserved and they will launch.

Relative to the train, and by extension the portal, the people are moving towards it at the same speed as the train relative to the ground, since the people are tied to the ground. I'm gonna work with the definition of momentum that equals it to the velocity of an object times its mass, and with the assumption that the portals conserve mass and momentum of the objects during teleportation, or with negligible losses. Having found that the momentum stays constant, and given the mass before and after teleportation is constant, the velocities relative to the portal are gonna be constant too. (p1=p2 <=> mv1=mv2 <=> v1=v2). And since the velocity of the people relative to the portal is the velocity is the train relative to the ground, and the velocity of the train relative to the ground is far bigger than the velocity of the people relative to the ground, the answer is gonna be B, where the people shoot out of the portal with great speed.

If the people actually go into the portal and not under it that is.

How can it not be b? Every situation in the Portal games is already exactly like this, but with the portal fixed to a slab that moves with the rotation of the Earth, whereas in the drawing the portal moves as the sum of earth rotation + the movement of the train.

gonna go with a - the people aren’t moving when they go in, so they won’t be moving when they come out

I believe it should be A. People aren't moving, and the portal doesn't carry momentum. At most people would be appearing on the other side with very little delay between eachother resulting in the most recently teleported person violently pushing away the last one.

B. Velocity is relative.

Can portals exist on a moving object?

The train is not moving. The rest of the world is moving underneath it. Therefore, by the principle of "speedy thing go in, speedy thing come out", the people will be launched.

I think B and maybe it's easier to explain my reasoning with a more dramatic example. instead of people on a track, maybe the trolly is heading towards a 50 foot horizontal pole. when the trolly comes to the pole at 90mph, the pole is not moving. but after the trolley's portal has "swallowed" 40 feet of the pole, all 40 feet of that pole are exiting the portal at 90mph, being pushed by the 10 feet of pole that the trolly is still "swallowing", so the momentum of 40feet worth of pole would continue to launch the remaining mass of the pole out of the portal and it would be launched out instead of flopping to the ground.

if we go back to our people on a track example, I think this would also kill them as for people on either side of the portal, it would feel like they're being ran into at 90mph by the people on the other side of the portal.

did that all make sense?

If the train drives slow enough that is takes 3s between when your head gets through and your feed are trough, it also needs to take 3s on the other side or you are ripped to pieces or squashed.

Now if it takes 0.1s, you also have to come out in this time and will have a velocity, the same as the train.

Discussed this with some friends and the view we came to is that your momentum relative to both the portal and your surroundings is preserved (which explains how you could portal to the moon and not get liquefied by the difference in rotational momentum between earth and the moon). The portal speeds you up or slows you down depending on local conditions on the other side to preserve your relative momentum. This would, logically, indicate that energy is created or destroyed depending on the difference, which (to me) means that 'portals' technically exist outside our universe as a concept and are therefore not subject to conservation of energy.

B

Lets say the train is moving with 10 meters per second. That means that the people will enter the portal with 10 meters per second. Therefore, they will leave the other portal with, you guessed it, 10 meters per second. Henceforth, they will be traveling with 10 meters per second after leaving the portal. 10 meters per second.

There's a reason why in the game you could never put a portal on a moving surface

i still can't believe people think it's A

Is that guy wearing blue and black jeans or white and gold?

B for sure. Consider a long pole (stationary relative to the track) entering the portal at the front of the trolley, it would leave the portal at the speed the trolley is moving.

This is all irrelevant, portals can't be placed on moving objects.

Unfortunately, this isn't testable in Portal because portals can't be affixed to moving surfaces.

I would assume the people just plop out fine since they would retain their momentum (which is nil), and the portal's own momentum wouldn't be applied to them. But God damn it I wish I could just make a Portal map with a moving portal and see.