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/sci/ - Science & Math

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6088152 No.6088152 [Reply] [Original]

Science all up in this bitch please.

>> No.6088162

What's with people and these shitty portals problems. They can all be solved when you apply the basic restrictions of portals to them
1. The surface on which a portal lies cannot move, or the portal will dissipate.
That's it. So when red piston moves, orange portal dissipates, and you just slammed a box with a piston. Nice.

>> No.6088176

>>6088162
>The surface on which a portal lies cannot move, or the portal will dissipate.

Let's throw that in the trash. What then?

>> No.6088174

>>6088152
Assuming that the portal can move, then you would just get A. This is because the cube never had any motion to start with, and there is no force acting on the cube except for gravity and natural force.
If you moved the cube up into the portal, you would get B, assuming the platform the cube is sitting on cant go through the portal.
The answer to this question is Newton's first law of motion.

>> No.6088181

>>6088176
Read the rest of >>6088162
Or are you asking something else?

>> No.6088185

>>6088176
Not necessary. Motion is relative anyway. It's not the piston with a portal on it. It's the box that's sitting on the portal. The picture has just fixed focus on the box so it appears stationary in the absence of background objects for reference.

>> No.6088187

>>6088174
Consider the motion of the portal relatice to the cube.
cube leaves portal at the speed the portal engulfed it

>> No.6088195

>>6088187
Wrong. No force was applied to the box to force it from its stationary position. Newton's first law man,>>6088174 had it right

>> No.6088192

>>6088185
*box that's sitting on the piston

>> No.6088193

>>6088181
I'm asking what happens if the portal remains.
>>6088187
That's exactly what i'm thinking but can't quite be sure.

>> No.6088197

>>6088187
I think I see what you mean now. The box would move out of the blue portal with the same speed that the orange portal was moving, so the cube would have motion after all. Is that what you meant?

>> No.6088210

I assume that if the red piston stops after hitting the platform, you'll get A.

But i think that if the platform was to retreat and the piston maintained its momentum you 'd get B.

>> No.6088209

>>6088174
Forget the first part. That was not completely correct. As long as the orange portal was moving with enough speed, you would get B. This is because the cube would be MOVING out of the blue portal in a perpendicular direction to the blue portal. The orange portal would have to be moving with enough speed though that when the cube came out the other side, it would have enough speed to the force of overcome gravity.

>> No.6088217

>>6088197
We are on the same track now

>> No.6088226

Not OP, but here is another portal question.
Would the edges of a portal act as a perfect knife, able to cut anything? If an atom was lined up properly, could you cut that as well. This is assuming that portals are 2 dimensional by the way, having a length and width but no height.

>> No.6088230

Would the gravitational field also follow trough the portal?

>> No.6088239

>>6088230
Fuck you, you broke my brain.

>> No.6089340

The correct answer is A.

>> No.6089350

A, the box has no momentum.
The portal is just a hole, it does not apply any impulse to the box.

>> No.6089354

Imagine the red piston as a wall with a hole in it. Now, imagine the surface that holds the box as a car, and imagine the box as a box inside or on top of the car. Also let's apply this silly little thing to this example: when a car crashes to the wall, the wall wont break, nor move ie. the wall absorbs all of the energy without breaking/moving/anything. Same goes for the car, when the wall smashes into it.

The car does not fit through the wall, but the box does. Now, imagine a car going ~100km/h against that wall, with the box inside the car. The box will keep it's momentum as the car crashes into the wall thus making the box fly, like in B. BUT however we are not talking about that, we are talking about the wall coming to us at a speed of 100km/h so the box has no momentum. Now as I told you before; the car won't move when the wall crashes into it, thus the box will not fly anywhere, it will just pop out of the other end of the portal like A.
QED

Answer: A

>> No.6089377

the cube jumps out of the portal and dances cha-cha
/thread

>> No.6089419

>>6089354

That is not really a correct comparison. With the hole in the wall example, the space behind the wall is moving with the wall and also stops with the wall. But we are talking about portals. The space behind the portal-hole does not move or stop with the platform that holds the portal.

>> No.6089423

A sliding object does not *plop* (somebody needs read comic books more.)

An object at rest is an object at rest, so the closest would be A.

It's a question of how portals work. When you open a portal or wormhole, you are making two points in space touch each other, but not the next two. If said portal isn't formed in a dipole system, you can't enter said portal. If it is a dipole system, this requires that the distance traveled between each entrance can only approach zero; not be zero.

Let's expand this whole cube thing so that we can at least better identify what we see. Let's call the cube a die so that we can at least claim we are seeing the same face of the object. This doesn't help much actually.... ^_^

Given that the die is "always" not quite zero over the distance of the incline, but is perpendicular to the incline, a sliding effect can occur up until the reaches the edge of the of the portal. (in this case, the corners of the die would hit the circumference.)

As the materials are bound by the approaching zero system, we get stuck with the casimir effect. So the die most likely gets fused to the edge of the incline in an E 3 system which totally blows up the universe. (*maybe.)

The problem is that the die is present at 2 zero positions. It is both sitting on the pedestal and sitting on the incline at the same time. As such, the area covered by the portal is causing pedestal and the incline are also going through the casimir effect with themselves in addition to the corners of the die.

>> No.6089421

>>6089350

Momentum is relative you pleb.

>> No.6089431

Version 2:

The other option is that the casimir effect isn't quite as Quantum-ly bound as we normally think it is. In this case, we get to play with the rotational value of the portals. If the portal is positioned so that one of the surfaces is not perpendicular to the incline, then it is possible that the movement of the incline would cause a centrifugal rotation to the die as it sits there.

The rotational effect could cause the cube to shoot out if the buildup of force is sufficient to alter it's sum vectors. In this case, B would be inaccurate because it isn't showing a vector which is plausible. (die should be counter-spinning relative to the rotation of the incline. and not be just a tangent to a circle. Die should be showing a more then just a single dot.)

>> No.6089516

It's B here is why

The box doesn't move at start
The box doesn't move at B

Do not attempt to argue my IO is 140+

>> No.6089521

Moving portals cause conflicting frames of inertial reference, and thus are not covered under Newtonian physics.

Answer is C. None of the Above.

Move along.

>> No.6089538

>>6089521
so what would happen then

>> No.6089546

it's A the portal can't apply any force on the cube (or it would simply smash the cube under it), so the cube comes out and has the same impuls (or whatever force*mass is called in english) as before, so zero if you consider the original picture

>> No.6089553

>>6089538

Portals do not exist in real life, and we model their behavior assuming they obey Newtonian physics.

If Newtonian physics do not apply might as well ask how many calories does a unicorn steak have.

>> No.6089690

>>6089553
We can still approximate

>> No.6089706 [DELETED] 

Galilean invariance -> setup is equivalent to having the orange portal still and the cube going upwards, so B.

>> No.6089709

Galilean invariance -> setup is equivalent to having the orange portal still and the cube and blue portal going upwards, so A

>> No.6089737

>>6089709
This
If we set the reference frame to only include the block and the platform, all that is happening is that the force of gravity (and the corresponding normal force of the surface) gets shifted around. All the portal in game does is transfer, not accelerate.
If the bottom paltform was the one moving, then B would happen.

>> No.6089739
File: 124 KB, 696x618, 1293863661589.jpg [View same] [iqdb] [saucenao] [google]
6089739

>>6088152
there's no conservation of energy as no energy gets transfered to teh cube.

>> No.6089750

>>6089690
Then the approximation is that the portal surface is moving, therefore the portal will dissipate. That's how it works in the game.

>> No.6089756

This isn't science.

>> No.6089758

I'm still tempted to type out a long post explaining why B is more reasonable, but you should just read the archives for that. We've had this thread a billion times already.

>> No.6089773

Since when do portals conserve momentum? It's a vector quantity.

>> No.6089817

>>6088152
A.
/thread

>> No.6089819

>>6088174
> If you moved the cube up into the portal, you would get B, assuming the platform the cube is sitting on cant go through the portal.
The answer to this question is Newton's first law of motion.
This is happening. Lrn2reference frames

>>6088195
You obv don't know the full of Newton's Law or Galilean invariance.
An object in motion will stay in motion.
Since the only reference frame that matters is the portal's[1], the object is already in motion when it passes through the portal. So B, it will be launched at some non-zero velocity.
>>6088230
No, only momentum is conserved [1]
>>6089354
Again Galilean invariance says both of those scenarios are the same.
>>6089521
>>6089553
See [1]
>>6089773
As long as the mass doesn't change, the velocity vector is proportional to the momentum vector

[1] GLaDOS: "Speedy thing goes in, speedy thing comes out."

>> No.6089847
File: 38 KB, 1148x802, cube.png [View same] [iqdb] [saucenao] [google]
6089847

It'd be A.
I like to think it like pic related. Instead of a portal it's just a normal hoop or something.

>> No.6089871

"Speedy thing goes in, speedy thing comes out." =/= "Stationary thing goes in, speedy thing comes out."

>>6088162 is right anyway. Stop making these threads.

>> No.6089877

Oh boy, another chance to post this. Let us consider the general case of a point particle and two portals. Orange portal faces down, blue faces up, and the particle starts below the orange portal. All velocities are in the vertical axis, and there is no gravity. Positive velocity points up. The lab-frame velocities of the orange portal, blue portal, and point particle are <span class="math">v_o,v_b,v_i[/spoiler] respectively, and the particle's exit velocity is <span class="math">v_f[/spoiler]. We want a rule that tells us <span class="math">v_f[/spoiler] as a function of the other velocities.

First, consider a case we already know: <span class="math">v_o=v_b=0[/spoiler]. We know that in this case <span class="math">v_f=v_i[/spoiler]. Note that this makes sense, in that when <span class="math">v_i<0[/spoiler], we get <span class="math">v_f<0[/spoiler]. A negative <span class="math">v_f[/spoiler] means that the particle would exit the blue portal with a negative velocity. In other words, it would fail to exit at all, which makes sense, since <span class="math">v_i<0[/spoiler] is exactly the case in which the particle never enters the orange portal. So, could this be the general rule nonzero portal velocities? If it were, then case A above would be correct, so let us call it rule A. But we shall see that it cannot be the general rule.

To see why <span class="math">v_f=v_i[/spoiler] cannot be the general rule, consider the case where <span class="math">v_o\neq 0[/spoiler] but <span class="math">v_b=0[/spoiler]. We want our rule to have <span class="math">v_f>0[/spoiler] only when the particle will enter the orange portal, and <span class="math">v_f<0[/spoiler] otherwise. But consider the case where <span class="math">v_i=-1 m/s,v_o=-2 m/s[/spoiler]. In this case, rule A says that <span class="math">v_f=-1m/s[/spoiler], meaning it does not exit the blue portal, but we know that the particle will enter the orange portal. We need a rule that works in this case, and one such rule is rule B: <span class="math">v_f=v_i-v_o[/spoiler]. This is the rule that leads to case B above.

>> No.6089879

>>6089877 , cont.
Finally, consider the case when all velocities can be nonzero. Even rule B fails in this case, since there are cases when the particle goes in the orange but rule B says it doesn't go out the blue portal. For example: <span class="math">v_i=1 m/s,v_o=0,v_b=2m/s[/spoiler]. Rule B says the particle exits the blue portal at 1 m/s, but this is slower than the blue portal is moving, so the particle cannot exit. The only rule that works in this general case is rule C: <span class="math">v_f-v_b=v_i-v_o[/spoiler]. From this starting rule, it is possible to determine what force portals apply on objects, and what happens when we introduce extended objects, angled portals, transverse motion, etc.

>> No.6089891

Don't try to apply Newtonian mechanics to this problem. Even if you assumed that portals were some form of wormhole, rather than being pure fantasy bound only by made-up physics, you'd be doing it wrong.

Unfortunately there isn't a good answer based on the game engine. The experiment has been tried, and the cube doesn't pass through the portal at all, but gets pushed into the ground in a glitchy fashion. They will almost certainly fix the mechanics of moving portals if they ever use one in a game in a situation where you can actually interact with it.

http://www.youtube.com/watch?v=S85nudR6D-Y

As far as what the game should do, B is the answer that makes the most sense.

To see why, just analyze the situation when the block is halfway through the portal. It is entering the orange portal with a certain speed. It MUST exit the blue portal with the same speed (relative to the blue portal), otherwise part of it would either be duplicated (if it exits faster) or disappear (if it exits slower). It is reasonable for the block to retain that speed and continue as a projectile.

>> No.6089903

>>6089871
It's not stationary. l2 galilean invariance
It's moving towards the portal.

>> No.6089994

It all boils down to weather a moving portal can impart momentum to an object going through it.

We know stationary portals preserve momentum (AKA Speedy thing goes in, speedy thing comes out.) but we know nothing about the properties of them in motion.

And to those saying that coming out of the blue portal would necessarily impart momentum because of the speed it exits the portal, what if it's simply space folding itself to allow the transportation of the cube?

The problem is just undefined.

>> No.6090194

The answer is resolved by considering if their is gravity or not.

If there is gravity then the answer is A because the block will fall to the ground.

IF there is no gravity the answer is B.

We know this because the block comes out perpendicular to the portal in B. This is physically impossible because as soon as the head of the block came out it would feel a new gravity and begin rotating. It is not rotating and hence, solution B has no gravity.

Hence hence, the answer depends on gravity.

>> No.6090216

The answer is pretty obviously B
When the box leaves the portal it obviously has to have a speed, since it's moving
According to "newton's first law" people the box wouldn't even move through the portal, which doesn't make sense. It's obviously moving. Then if you say "what speed is it moving at?" it's clear that it's moving the speed the platform was moving at
There's plenty of other reasons why it's obvious B is the real one but this is the most simple argument

>> No.6090231

>>6089847
Both ends of a hula hoop are moving at the same speed
Both ends of a portal are not moving at the same speed
You can't compare the two

>> No.6090261

>>6090216

What if the box it's moving, but the space around it is?