this post was submitted on 26 Jul 2026
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Ragebait answers only

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[–] davidagain@lemmy.world 1 points 1 hour ago

Everyone else is wrong. (Ragebait.)

Speed of approach = speed of separation.

If the box left the blue portal at a slower speed than it entered the yellow one, the top of the box would be moving slower than the bottom of the box, which would compact the box dramatically during the transition, but we can see that its size is unchanged and it is still square.

The top of the box is pushed rapidly out of the blue portal by the bottom of the box being thrust into the yellow portal. (The bottom of the box is pulled rapidly up into the air by the top of the box which is already moving quickly.)

[–] saigot@lemmy.ca 2 points 22 hours ago

It should be a.

Imagine if the cube was actually a long rod and the orange portal start with the column half way inside it. Then the orange portal moves, in this case it would be very odd for the rod to jump in this scenario like in case b, the thing you would expect would be for the rod to stay still (besides tipping sideways a bit) consistent with case a.

[–] Ibex@lemmy.world 22 points 1 day ago (1 children)

The object going into the portal has no momentum so it would be A.

[–] flying_sheep@lemmy.ml 4 points 1 day ago (7 children)

No momentum in relation to what? Momentum doesn't exist in isolation.

[–] philipp_@discuss.tchncs.de 9 points 1 day ago

Momentum relatively to the source game engine grid.

[–] SirActionSack@aussie.zone 4 points 1 day ago (1 children)

"speedy thing go in, speedy thing come out."

So A.

[–] flying_sheep@lemmy.ml 2 points 1 day ago (1 children)

As I said, there is no “speed” in isolation. Speed is a relative property of an object and a reference frame (i.e. another object, like e.g. a planet)

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[–] Fedegenerate@fedinsfw.app 8 points 1 day ago

"Speedy thing goes in, speedy thing comes out" as the cube isn't a speedy thing (no speed lines) going in, it won't be a speedy thing coming out.

[–] MrRandom@lemmy.zip 9 points 1 day ago

neither, no portal rules were given. Please create an Aperture support ticket.

[–] codexarcanum@lemmy.dbzer0.com 19 points 2 days ago

Portals aren't real and so work however you want them to, but people rarely consistently apply their models.

I'd say A given how they work in the games though. Only the object's momentum is conserved. The portal doesn't transfer momentum. There may be a slight breeze coming out of the blue end as the column of air in front of the portal-plate is pushed in, but the cube is just going to flop out.

[–] bitjunkie@lemmy.world 18 points 2 days ago

Speedy thing did not go in

[–] Crozekiel@lemmy.zip 5 points 1 day ago (1 children)

You can't put a portal on a moving platform, it has to stop moving first, so neither can happen... Unless the moving surface is a celestial body at least the size of The Moon, I guess?

What!? What if the platform is a train on Earth?

[–] myotheraccount@lemmy.world 9 points 1 day ago (3 children)

Neither. The cube is not making contact with the portal at all, since the portal is on a stationary block with some speedy lines drawn on it. Speedy lines don't nake thingy go fast - everyone witb a gel-hairstyle knows that.

EVERY GIT KNOWS FAST LINES AIN'T DA TRICK! RED IZ WOT MAKES THINGS GO FAST!!!

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[–] Olgratin_Magmatoe@slrpnk.net 35 points 2 days ago (1 children)

Niether. Moving surfaces break portals instantaneously.

[–] brockhold@lemmy.world 9 points 2 days ago (1 children)

Portal 2 has moving surfaces, with the cop-out that it's accelerating surfaces that cause the portal to break.

spoilerNo matter that you literally put a portal on a different planet...

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[–] zephiriz@lemmy.ml 6 points 1 day ago (1 children)

Was going to post the correct Answers (A) but then looked at the post and though na. But if you want to know more about portals and how they would work in real life check this out. Great guy.

https://youtu.be/1zgBwQVr-wI

[–] Peffse@lemmy.world 398 points 3 days ago (5 children)
[–] ThatWeirdGuy1001@lemmy.world 93 points 3 days ago (2 children)

Stop stealing all my upvotes

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Perfectly understood the assignment, 10/10, no notes.

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[–] UnderpantsWeevil@lemmy.world 31 points 2 days ago (5 children)

Ragebait answers only

I'm giving so many people Fs on this assignment because you failed to read all the instructions.

The correct answer is B due to the graphical conservation of speed lines.

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[–] moakley@lemmy.world 4 points 1 day ago

The top of that masher is clearly protecting the cube from the rain, so I'm not sure how the rain is expected to shoot the cube out as in option B.

A.

[–] TheOakTree@lemmy.zip 2 points 1 day ago* (last edited 1 day ago)

If you considered the cube to be 1m^3 , the time at which the cube enters the orange portal t1, and the time at which the cube fully exist the blue portal t2, then the speed of the cube relative to the world outside of the blue portal would be 1m / (t2-t1).

Assuming the cube maintains this speed after exiting the blue portal, it would behave as in scenario B.

[–] Azrael@reddthat.com 7 points 2 days ago (1 children)

It would probably be A because of Newton's first law of motion.

[–] justme@lemmy.dbzer0.com 10 points 2 days ago

because of that law it is B ;). the cube "teleports" into the reference frame of after the portal and in this frame it is highly in motion.

it's like you trying to jump on to a moving train, you first need to match the trains velocity (speaking relative to earth), then you are at rest in the trains frame.

this kind of thoughts is what makes special relativity so cumbersome.

[–] mirshafie@europe.pub 28 points 2 days ago (2 children)

B.

Momentum/velocity is not an intrinsic property of an object, it is a relative property between two objects in a frame of reference.

Behind the yellow portal is the part of the universe where the blue portal is. The yellow portal, and therefore the space where the blue portal is, has momentum relative to the cube.

Put yourself in the frame of reference of the cube. You see the yellow portal come toward you. Imagine there are objects on the other side of that portal. You see those objects rush toward you through the portal. Why would the objects just stop dead when you came through the portal? (If they did just stop, it would be as though you hit a wall, and you wouldn't actually go through the portal at all.)

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[–] surewhynotlem@lemmy.world 71 points 3 days ago (5 children)

This was answered decades ago

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The real answer is the enemies we made along the way

[–] whereitsat@lemmy.zip 4 points 1 day ago

you know only engineer/computer science nerds post on lemmy because nobody has called out that the box looks like the box from hellraiser.

no matter what you do to it, you'll probably end up in hell.

[–] Tigeroovy@lemmy.ca 34 points 2 days ago (7 children)

Portals don’t stay on moving platforms.

But if they did, it would be A as the cube itself has no momentum.

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[–] ChaoticNeutralCzech@feddit.org 12 points 2 days ago (1 children)

https://www.youtube.com/watch?v=B19nlhbA7-E

Not providing a link to alternative platforms is my ragebait

[–] bss03@infosec.pub 4 points 1 day ago

In addition https://www.youtube.com/watch?v=DydIhwLrbMk which tries to make portals act "real" by treating them as spacetime with an unusual (but not mathematically disallowed) geometry.

Yes, they are fictional, so they behave however Valve (and fan works) want them to behave, but trying to bridge the gap between fictions and current physics models and be a fun and enlightening experience.

[–] TotallynotJessica@lemmy.world 126 points 3 days ago (12 children)

You can't place a portal on a moving surface in either game, so neither.

[–] lime@feddit.nu 77 points 3 days ago (5 children)

you can in one specific spot in portal 2!

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[–] MacNCheezus@lemmy.today 1 points 1 day ago

Portals aren't real, you know.

More importantly, what if I straddle the blue one?

Img pls?

[–] BlackLaZoR@lemmy.world 6 points 2 days ago (1 children)

It's a superposition of both states until you make a measurement

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