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T(rule)y Problem
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this post was submitted on 18 Aug 2023
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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.
So you're saying that Portal is an accurate physical simulation of reality that should be used to base proper scientific conclusions on?
You're saying that there should be such a thing as a "proper scientific conclusion" to this meme about a video game physics engine? The only definition of these portals that we have to work with is the definition in the Portal physics engine. There is no definition of anything that behaves like these portals in the scientific study of physics. It is meaningless to try to draw a scientific conclusion about something that does not have a scientific definition.
Oopsie again. Try reading what was written.
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.