Gotta be B, right? But then if the victims had no momentum... ah this hurts my brain
this post was submitted on 18 Aug 2023
214 points (99.5% liked)
196
16552 readers
1886 users here now
Be sure to follow the rule before you head out.
Rule: You must post before you leave.
founded 1 year ago
MODERATORS
I think it would have to be B due to the laws of relative motion. It was easier for me to think about when I considered the opposite case. Imagine someone is on a vehicle, for example a boat, with one portal on the boat and the other on the shore. You wouldn't expect someone casually walking through the portal on the boat while it's moving to suddenly experience the momentum of the boat after exiting. This is because the person and the portal are both experiencing the same motion.
Going back to the original scenario, the relative motion of the people entering the portal is as fast as the trolly is moving. If there was no portal, they would experience the same force if the trolly ran into them as they would if they ran into a stationary trolly at the same speed.
You have to do funny things with the conservation of momentum when dealing with hypothetical portals because the portals allow you to abruptly change the frame of reference.
Well in the portal games I don’t think portals have ever moved
But the way I see it the “distance” you travel through the portal is the same. You don’t go through a tunnel it’s instantaneous. But one portal is moving so I think just and endpoint is moving
I’m thinking of it like a normal door
If a run through a door I will inherit my momentum like in the portal games
But if a door is quickly coming at me and I’m standing still the frame just goes around me I’m still
But if the door is coming at you fast, isn't the 'room' too?
Yes but
AAAAAAAAAAAAA
Yeah but I don't think the portals can distinguish relative speed, and so it would just see you moving through the portal at 60 mph or whatever and shoot you out at 60 mph at the same angle relative to the portal.
There is ONE case of portals moving and it was specially coded because you’re right that they usually don’t.
Momentum is relative. Whether the victims move to the trolley or the trolley to the victims doesn’t make any difference.
Momentum is transferred from the trolley to the victims. In order for energy to be conserved, when they accelerate, the trolley will slow down. Now that you think about it it's not that different from being hit by a trolley that has no portal on it
As per the games own physics it's A.
Speedy thing goes in. Speedy thing comes out. It doesn't matter if the portals are moving even in the game. The only thing that matters is the momentum of the object moving through the portals.
All y'all physics nerds can take your degrees and shove em cause it's video game logic not real life.
The only reason the portal velocity isn't considered in the game is because the portal velocity is always 0. Moving portals just isn't something they programmed it to do. If they had, I imagine it would be B, if only because it creates more interesting gameplay options.
Kid named neurotoxin generator level:
load more comments
(2 replies)
A, because the portal has the momentum not the people on the tracks?
The people have to exit the portal at the same speed they enter, otherwise they'd have to be squished or something weird.
If 1cm of person enters in 1 second, 1cm of person needs to leave in that second, the only other options are that part of the person disappears or gets compressed to less than 1cm.
Motion is relative though. Both the portal and the people are presumably on earth (or any other planet) and will thus be moving around in space at a fast pace. So the people have momentum, just not relative to the earth (or I guess more specifically not relative to the specific patch of earth they're on).
So there's 2 options:
- Portals do not respect the laws of relative motion -> the people will get yeeted in some direction because the earth they're on goes very fast through space and the portals are not pointing in the same direction
- Portals do respect the laws of relative motion, in which case the people will get yeeted with the speed of the train
The fact that people say A honestly makes me a little bit worried about the state of physics education
Like.. they enter at speed, why would they not exit at that speed?
Because they don't "enter at speed". The portal is moving ; not them. To them, they haven't actually moved.
So like i said, i worry about the state of physics education.
Motion is relative, things don't have some magical hidden speed variable tracked by god, all that matters is how things move relative to other things. This is fundamental physics.
No need to be insufferable. I'd rather a good explanation, if all you have are indirect insults you can keep those for yourself.
I will however admit I wasn't always the most focused student in physics class, and so my perspective may be flawed.
In any case, I don't quite see how a portal is different from an empty window frame. It's just a hole. The hole going towards the cube, and the cube "going through" the hole, should not create any motion relative to me. And yet, it does ?
Even relative to the blue portal, the cube went from 0 motion to have motion. How does that work ?
I'm guessing this will all boil down to "portals aren't possible" but idk.
Imagine the following:
Point A is traveling towards point B at a speed of 50km/h
Point B is traveling towards point A at a speed of 50km/h
In these instances, the distance between point A and point B decreases at the same rate. This means there is the same amount of energy, the same amount of force, being provided towards each other. Which one is moving is irrelevant, just so long as the total energy putting them closer together is the same.
In both instances, they would collide with the force and energy necessary to move 50km/h at their respective masses. For this exercise, let’s say they’re both 100kg. This means the energy required to move a 100kg object 50km/h is approximately 9.6 kilojoules. This means 9.6 kilojoules of energy must be used to accelerate them, and 9.6kilojoules will be dissipated into each other in the event of a collision.
In this case, however, rather than colliding and dissipating the energy into the crash, there is another option.
Tf you have a portal, it’s essentially a door to a room. If you run towards the door, or the room moves closer to you with the door open, you still enter the room at the same speed, with the same forces acting upon your body.
So the only logical conclusions that can come of this are the following:
Either the portals obey the laws of relative motion, (meaning all of the factors I described are the only factors to worry about) or they don’t. If they do not, that means absolute motion must be taken into account, including the absolute point in space the earth was, the velocity at which the earth spins, etc. Since this is clearly not demonstrated in the Portal games, the only logical conclusion is this:
As the portal accelerates towards you, (or you accelerate towards the portal) your body must move with the forces necessary to accelerate at the speed at which the collision would occur. In other words, if you weigh 100kg, and the trolley is traveling towards you at 50km/h, your new velocity will be perpendicular to the exit angle of the second portal with 9.6 kilojoules of energy affecting you.
I hope this explains why option B is the right answer
Imagine your example of an empty window frame, but in an empty void, with no points of reference other than the important objects. You could see this interaction in two ways. The frame moves towards the people, around the people, and then away from the people or the people move towards the frame, through the frame, and than away from the frame. This is the same interaction. It does not matter which is "moving", either one results in the same interaction.
In this portal case, you combine the two methods of observing the interaction. The portal moves towards the people. The people go through the portal. The interaction now says the portal moves away from the people, but this second portal is stationary. So you flip how you look at it. The portal now "moves" away from the people by the people moving away from the portal.
Hopefully this makes sense.
But if you draw out the velocity vectors, the portal and people would have a would have a positive differential.
Imagine a building comes flying at you and but you barely jump into the window. To you, you're not moving, but everything else around you is. It would be the same principle if a moving portal came flying at you.
What happens to a pole?
If the portal approach you as you hold it then the other end needs to be moving in it's local space outside the second portal. That means it is given momentum which must come from the portal, likely taken from the momentum of the first portal which is moving. Also, the far end of the pole will likely experience a degree of inertia and push on the end you're holding (at an equivalent of half the speed of the portal).
Whoopsie. Maybe take another look at how portals are handled in the game. Then extrapolate that to this "conundrum "
The answer is neither. They wouldn't be ejected at all theyd just fall right back into the portal. Which would make them fall back through the orange back and forth forever. Until someone grabs the blue portal wall and pulls them out.
load more comments
(3 replies)
Yeah, I'd be a bit more careful about making statements on physics education. The setup in itself is breaking physics itself. Arguing about what would happen is like saying "if we ignore the rules, what would happen according to the rules?". It's theoretical either way and there's no correct answer.
B, even as the people do not have momentum, the portal does. Think of it this way, the first person coming out of the portal, let's say they are having zero speed, but he is right infront of the portal, the second person to exit will exert a force on the first person to move and create space so that the second person can be next to the portal. What speed is this second person coming through the portal, why that will be similar speed to the moving portal. Only if the second portal is moving away at a similar speed will the people experience a situation like A, but as can be seen portal A is fixed to an angled block
Yeah, this is my interpretation as well. The people have to have momentum as they exit the portal, to make room for the other mass to exit if for no other reason.
It's A. Object momentum is the only part that matters to portals, so they would just plop down.
Motion is relative, there is no sationary reference frame. From the reference frame of the portals, they do have momentum going towards the portal
load more comments
(1 replies)
The portal is not below them. They are all run over and some blood and guts either shoot out or spill out.
B, because position and speed are relative,
it would slow the train down equal to the momentum gained by the people.
A. If I move a large hula hoop over your body, you don't go flying out the other side. Portals are just large hula hoops with either side in different places.
A hula hoop would be two portals facing opposite directions. Not the same scenario at all. First portal accelerates the object, second traveling in the opposite direction decelerates it equally resulting in a net zero. If the second portal doesn't move with the opposite direction or speed, then it won't cancel out. The moving portal would have force exerted on it in order to equal out the energy of accelerating the victims
I think in this scenario it's pretty clearly B. Though I have a secondary scenario. What if you're standing against a wall and the portal slams into that wall. You're against the wall but the wall itself never goes through the portal. Would you still get launched then? The portal is still moving when you go through it but stops abruptly as soon as it reaches the wall. You're still physically touching the wall that's now on the other side of the portal. Would you get forced off of it and launched?
load more comments
(1 replies)
I was team A, but after thinking all morning I'm team B
Imagine the exit portal is on the back of the trolley, it doesn't even have to be a portal, even just imagine it's an open hole in the front and back of the trolley. As it approaches you jump up, enter the front and exit the back without landing, you then land where you started. See how in this case your momentum doesn't change because both portals are moving at the same speed. If the exit portal isn't moving, you'll gain that momentum.
B, final answer. Who tests this?
Since their heads and feet would be outside of the portal, neither of the choices are correct, because in both choices they are uninjured at the pictured time.
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?
Portals already are infinite energy machines. Just out a portal up higher than the other one, and you get infinite energy generation via gravity.
dammit, you just explained why they can't exist
...
Fuck.
Portals already break the laws of physics. The virtual world inside the orange portal is moving at the same velocity as the trolley, think about how much kinetic energy that is
I don't think the portal contains anything within itself, though. The portal is a non-entity - it's just that if you pass through the portal, you suddenly find yourself in a different location, as if that location were right next to you. The portal itself has no other properties of its own, I'd think.
I think in the hypothetical scenario of a magically self sustaining portal that seemingly generates its own energy to keep active, energy would be applied to the people via the portal
This still assumes that the portal is an infinite-energy machine, though, which I think is unwarranted and creates more difficulty than is necessary. I would assume that the portal itself has no properties and does not act on other objects.
load more comments
(2 replies)
view more: next ›