B since all movement is relative.
This was a triumph.
A, since portals cannot transfer momentum from the tram to the victims.
To put it another way, if you were standing and the portal was pushed towards you by a tram, do you think you would be launched out of the other side at that rate?
There might be some increase in momentum as the part of you that went through the portal first gets pushed forward by the parts of you that get pushed forward after, but it's not going to be as dramatic as the momentum you would have received being hit by the tram.
Most likely you would stumble forward and fall down or have to catch yourself.
Portals maintain velocity. Velocity is relative. Therefore the velocity they maintain is the relative velocity of the portal and the subject. Any other way and there would be no consistent way to pass any moment when passing through a portal.
After thinking about it longer then i care to admit I think i finally agreed with you.
As you said it is all relative, from the prospective of the moving portal. You could say it isnt moving at all but the entire world around it is moving, thus when people enter the portal from the portal's prospective they people are the ones moving and will continue moving when they exist.
Hmm tlnit that i typed this out I feel like i didn't do a very good job. Owell the answer is B.
The reason this is so confusing with different answers is that the portals don't really exist, so inherently whether you say a or b is gonna depend on assumptions. In game they aren't allowed to move so we have nothing to base it on to match game physics.
Here's my take, momentum is a product of velocity. Velocity needs a reference frame. Without it, there's no real difference in saying the portal has a velocity of 0 and the people tied up have a the velocity and therefore momentum, or the other way around. If we assume velocity with respect to the portal is what matters and is the momentum carried forward, then it should be B. If it's relative to the earth or tied up people, then A.
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?
For whatever reason I feel more willing to break conservation of momentum than I am to
Obviously A
starts world war 3
Yeah definitely A. The momentum of the object going through the portal matters not the objective that has the portal on it.
But how would the objects get on the other side then? The receiving side isn't moving, so the objects essentially need to be pushed through the portal at the speed at which the train is moving, resulting in B. The only way A could work would be both portals moving at the same relative speed.
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?
In classical physics you would be right, but in modern physics there is no standard frame of reference. It's equally correct to think that the people are still and portal is moving as it is to think that portal is still and people go in it immn fast speed.
Regardless, people and portal have large speed difference going in, so there will be large speed difference going out.
But portals can create energy. Put one above the other face to face and drop an object into the bottom one, it now has infinite potential energy.
Speedy thing goes in, speedy thing comes out
E: I was just quoting GladOS..... Not really thinking about the actual physics!
Yeah but the thing isn't moving the portal is, and the energy has to come from somewhere if the portal makes the thing go fast.
The energy would come from the trolley. The people would launch out at approximately the same speed as the trolley interacts with them and the trolley would slow down in response to how much kinetic energy was transferred to the people.
This is correct. The motion of the people is relative to the Portal. It doesn't matter if the trolley is accelerating the Portal towards them or something is accelerating them towards the Portal. Therefore they accelerate out of the other side with some retained momentum. Technically it probably resembles something in between pictures A and B.
This reminds me of the experiment about whether an airplane could take off from a treadmill.
Conservation of momentum says B I would think. From the protal's reference frame, the people are moving fast toward it.
The portal is a hole. The hole is moving. The conservation of momentum is the hole moving as it continues to move along the track. If the people start moving, where does that momentum come from?
Imagine a tennis racket with no strings. Two portals are stretched across the space the strings would normally be, back to back, one orange one blue. If you threw a ball in the air as if you were going to serve and swung the racket, the ball would pass straight through the portals as if they weren't there and would fall straight down due to gravity. The ball maintains its conservation of momentum, and the tennis racket holding the portals also maintains its conservation of momentum as it swings through the air. There is no force applied by a hole.
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.
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.
gonna go with a - the people aren’t moving when they go in, so they won’t be moving when they come out
Can portals exist on a moving object?
Not in the regular game, there are mods/fan games that allow it though.
There is one segment in Portal 2 where you need to cut some tubes that transport neurotoxin, and for that small segment only, the game allows moving portals. https://youtu.be/OrAHvenjZpA
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.
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.
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?
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
This is all irrelevant, portals can't be placed on moving objects.
The earth is a moving object, so all portals are moving through 3d space at all times.
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.
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.
