Bad physics in trailer

alpha_centauri_ · 07-13-2011, 11:40 AM

I don't know if anyone besides me cares about this, but I am a bit disturbed about the claims in the Portal trailer that say that momentum is conserved while entering a portal. As everyone knows, momentum = mass x velocity, and velocity is a vector. See where I'm going here? Although it doesn't sound as cool, it should be advertized that speed is maintained being that it is independent of direction while velocity is not.

Maybe the portals don't teleport what passes through them at all, but shift all of space so that momentum is conserved? While this introduces many more physics problems, I guess it would make the statement "momentum is conserved" true, otherwise it would be the only exception to that rule.

Before anyone tells me "C'mon, it's just a game, things don't need to be correct according to physics!", I'd like to point out that the word "momentum" simply needs to be replaced with the word "speed". Anyone who got through high school physics should know that.

Zekiran · 07-13-2011, 12:21 PM

Maybe in your universe.

But in CAVE JOHNSON'S universe, things are different.

ZZUBYTTIHS · 07-13-2011, 08:27 PM

First off I know nothing about physics lol.
I look at space like a sheet of paper, if you fold the paper and punch a hole (a portal) I can't see why you would lose speed passing through it like a doorway. unlike a teleport, you end up getting destroyed and rebuilt. hell I'm not even sure how the portals in the game are supposed to work.

you got me

iRaphael · 07-20-2011, 08:30 AM

Actually, I have to disagree... Think about this: You're in a building. You place a portal on the ceiling of the first floor and the other portal on the floor of the second floor. If you jump into the second portal, you will come out on the other portal following the same trajectory as you entered the first one. In this case, the portals work just like a hole on the floor: If you jump in a diagonal trajectory, you will come out following the same trajectory. The same goes for portals that are not placed like I mentioned: If you jump in a portal on the floor, in a diagonal trajectory, you will come out on the other in a diagonal trajectory, no matter where this portal is places (floor, ceiling, wall, etc). Remember when you place both portals on the floor and put something in it? The reason why we can't maintain it jumping around for a long time is because it would require a much precise trajectory, and we are humans... if the trajectory we put the object is a little diagonal, it will come out the other portal diagonally, making it fall off the portal and fall on the floor next to it. Following this thinking, I would say that, yes, trajectory is maintained through portals and, therefore, the velocity vector is also maintained. This way, using the expression "momentum is maintained" is correct. What do you think?

alpha_centauri_ · 07-20-2011, 11:20 AM

In your first example you are correct that momentum is conserved however it is not in your other examples. The trajectory is maintained out the second portal relative to the first but usually momentum is not. Like I said earlier, momentum is velocity * mass and velocity is a vector. The two parts of the velocity vector are speed and direction.

Now here's an example of my own. The two portals are on the north wall of a room. You travel north at 3.5 m/s. After passing through the portal you are traveling south at 3.5 m/s. Obviously the direction of travel has changed, therefore the velocity has changed, therefore momentum was not conserved.

iRaphael · 07-20-2011, 08:30 PM

Quote:

Originally Posted by alpha_centauri_

Obviously the direction of travel has changed, therefore the velocity has changed, therefore momentum was not conserved.

That is relative! Let's forget gravity for a moment and pretend I can move in any direction, in a straight line, at the same speed, for how long I want.
If you are seeing as an outsider point of view, yes, I started to move downwards, went through a portal, came out on the wall portal and now I am moving horizontally. However, if you look at it in my point of view, I haven't changed direction at any time. So, to me, I am still moving in a straight line, therefore, speed and direction were maintained. And so was momentum.

+ Plus: To change the direction of an object, you need a force. That is also basic physics. Since there isn't any force (told u, forget gravity), in my perspective I didn't change direction.

alpha_centauri_ · 07-20-2011, 10:40 PM

Quote:

Originally Posted by iRaphael

That is relative! Let's forget gravity for a moment and pretend I can move in any direction, in a straight line, at the same speed, for how long I want.
If you are seeing as an outsider point of view, yes, I started to move downwards, went through a portal, came out on the wall portal and now I am moving horizontally. However, if you look at it in my point of view, I haven't changed direction at any time. So, to me, I am still moving in a straight line, therefore, speed and direction were maintained. And so was momentum.

+ Plus: To change the direction of an object, you need a force. That is also basic physics. Since there isn't any force (told u, forget gravity), in my perspective I didn't change direction.

I don't mean to get into a pointless internet argument here, but I'm still not sure you understand the direction part in a vector.
Perspective means nothing, the point is that you are no longer traveling in the same direction you were before entering the portal. If you were holding a magnetic compass the needle would spin 180 degrees. That is not the same direction no matter how you perceived it.

Again, I understand this is just a game and nothing to get upset about. All I'm saying is that speed, not velocity (and therefore momentum) is conserved.

A basic rule of physics is that momentum is always conserved, so the physics in the game doesn't make sense anyway. I'm not complaining about that though, because it's awesome.

Like I said in my first post, one way that would make basic physics laws still apply is if space is shifted so that the portals temporarily occupy the same space and then shifts back within the same instant. This may sound crazy... and you're right. It's quantum mechanics. The fun part about quantum mechanics is that it doesn't make any sense, and nobody knows what's going on.

Another idea is that the entire game is actually a computer simulation where every subatomic particle is individually rendered, acted upon by real-world physics (allowing for some exceptions) coded into the simulation. The creepy part of this idea is that it is completely possible. It's already been done, granted on a MUCH smaller scale involving only about 200 atoms of copper.

Physics is fun, I wanted to major in it for quite awhile before I realized that engineering pays a lot more!

iRaphael · 07-21-2011, 07:07 AM

Perhaps the entire room shifts like you said... It makes sense, even though it doesn't (like you said, it's not supposed to...)

All i was saying is that, in my perspective, The portals acted like the "hole" in the first example. I never changed the direction I was moving. But it's ok. I don't have to be right (hell, I don't even know if I am! You said you're going to major, I am in the first year of High School!)

-Bai

ZZUBYTTIHS · 07-21-2011, 05:48 PM

You guys went over my head haha.

I would have to say quantum mechanics effect in a computer simulation. Since we can do things that kinda break the rules, not just bend them. I think... this would be an example http://www.youtube.com/watch?v=KRjRpTj_cqQ

First orange portal I aim a little to the right, this keeps me off the wall, and helps me land on the platform, nothing strange or rule breaking there. but after the second portal fling I seem to pick up speed somewhere.
I do this by duck/jumping as I enter the portal. you might have had this happen by mistake when just walking through one, sometimes you come out with way more speed than you entered.

_NJD_ · 07-21-2011, 08:12 PM

Speedy thing goes in. Speedy thing comes out.

alpha_centauri_ · 07-22-2011, 02:00 PM

Quote:

Originally Posted by _NJD_

Speedy thing goes in. Speedy thing comes out.

Yes, speed is maintained.

nrnoble · 07-22-2011, 03:10 PM

Actually, in the game it states:

"Speedy thing goes in, Speedy things comes out"

Now if you think about it for a moment... what are they talking about :P

But ya now, at some point ya just have to let some things go because when they made Portal, they weren't trying the save the world.

Dinosaur Rex · 08-02-2011, 12:19 AM

It keeps it's momentum, just the direction of the forces changes, It's like making a hole through the earth, when you reach the center of the earth, the gravity force equals zero, but you can't just stop there, the energy is in there, so you come out at the same height you threw yourself into that hole but on the other side. If you are taking this to a theoretical level, make the equations.

rent-a-hero · 08-07-2011, 02:42 PM

momentum... ok, mass x velocity, a vector....

so, the question is: where or what is your referencial point?

if its chell or one of the same pair of portals , i think momentum is conserved.

always remenber, if in the future laws of physics do not apply, god help you.

alpha_centauri_ · 08-07-2011, 05:56 PM

Ummmm... I really don't think you guys understand... If you exit a portal not in the same direction you entered momentum is not conserved. I keep saying momentum is a vector... Please, nobody post anymore without reading what I said first and with a knowledge of physics.

Again, I don't really care that the game made the mistake of saying "momentum" instead of "speed", but please stop saying that momentum is conserved. It isn't.

07-13-2011, 11:40 AM	#1
alpha_centauri_ Join Date: Jul 2011 Reputation: 1 Posts: 43	Bad physics in trailer I don't know if anyone besides me cares about this, but I am a bit disturbed about the claims in the Portal trailer that say that momentum is conserved while entering a portal. As everyone knows, momentum = mass x velocity, and velocity is a vector. See where I'm going here? Although it doesn't sound as cool, it should be advertized that speed is maintained being that it is independent of direction while velocity is not. Maybe the portals don't teleport what passes through them at all, but shift all of space so that momentum is conserved? While this introduces many more physics problems, I guess it would make the statement "momentum is conserved" true, otherwise it would be the only exception to that rule. Before anyone tells me "C'mon, it's just a game, things don't need to be correct according to physics!", I'd like to point out that the word "momentum" simply needs to be replaced with the word "speed". Anyone who got through high school physics should know that.

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07-13-2011, 12:21 PM	#2
Zekiran Join Date: Jun 2008 Reputation: 3967 Posts: 20,722	Maybe in your universe. But in CAVE JOHNSON'S universe, things are different.

07-13-2011, 08:27 PM	#3
ZZUBYTTIHS Join Date: Jul 2004 Reputation: 57 Posts: 460	First off I know nothing about physics lol. I look at space like a sheet of paper, if you fold the paper and punch a hole (a portal) I can't see why you would lose speed passing through it like a doorway. unlike a teleport, you end up getting destroyed and rebuilt. hell I'm not even sure how the portals in the game are supposed to work. you got me

07-20-2011, 08:30 AM	#4
iRaphael Join Date: Jun 2011 Reputation: 30 Posts: 42	Actually, I have to disagree... Think about this: You're in a building. You place a portal on the ceiling of the first floor and the other portal on the floor of the second floor. If you jump into the second portal, you will come out on the other portal following the same trajectory as you entered the first one. In this case, the portals work just like a hole on the floor: If you jump in a diagonal trajectory, you will come out following the same trajectory. The same goes for portals that are not placed like I mentioned: If you jump in a portal on the floor, in a diagonal trajectory, you will come out on the other in a diagonal trajectory, no matter where this portal is places (floor, ceiling, wall, etc). Remember when you place both portals on the floor and put something in it? The reason why we can't maintain it jumping around for a long time is because it would require a much precise trajectory, and we are humans... if the trajectory we put the object is a little diagonal, it will come out the other portal diagonally, making it fall off the portal and fall on the floor next to it. Following this thinking, I would say that, yes, trajectory is maintained through portals and, therefore, the velocity vector is also maintained. This way, using the expression "momentum is maintained" is correct. What do you think?

07-20-2011, 11:20 AM	#5
alpha_centauri_ Join Date: Jul 2011 Reputation: 1 Posts: 43	In your first example you are correct that momentum is conserved however it is not in your other examples. The trajectory is maintained out the second portal relative to the first but usually momentum is not. Like I said earlier, momentum is velocity * mass and velocity is a vector. The two parts of the velocity vector are speed and direction. Now here's an example of my own. The two portals are on the north wall of a room. You travel north at 3.5 m/s. After passing through the portal you are traveling south at 3.5 m/s. Obviously the direction of travel has changed, therefore the velocity has changed, therefore momentum was not conserved.

07-21-2011, 07:07 AM	#8
iRaphael Join Date: Jun 2011 Reputation: 30 Posts: 42	Perhaps the entire room shifts like you said... It makes sense, even though it doesn't (like you said, it's not supposed to...) All i was saying is that, in my perspective, The portals acted like the "hole" in the first example. I never changed the direction I was moving. But it's ok. I don't have to be right (hell, I don't even know if I am! You said you're going to major, I am in the first year of High School!) -Bai

07-21-2011, 05:48 PM	#9
ZZUBYTTIHS Join Date: Jul 2004 Reputation: 57 Posts: 460	You guys went over my head haha. I would have to say quantum mechanics effect in a computer simulation. Since we can do things that kinda break the rules, not just bend them. I think... this would be an example http://www.youtube.com/watch?v=KRjRpTj_cqQ First orange portal I aim a little to the right, this keeps me off the wall, and helps me land on the platform, nothing strange or rule breaking there. but after the second portal fling I seem to pick up speed somewhere. I do this by duck/jumping as I enter the portal. you might have had this happen by mistake when just walking through one, sometimes you come out with way more speed than you entered.

07-21-2011, 08:12 PM	#10
_NJD_ Join Date: Jun 2011 Reputation: 32 Posts: 100	Speedy thing goes in. Speedy thing comes out.

07-22-2011, 03:10 PM	#12
nrnoble Join Date: May 2008 Reputation: 1123 Posts: 7,669	Actually, in the game it states: "Speedy thing goes in, Speedy things comes out" Now if you think about it for a moment... what are they talking about :P But ya now, at some point ya just have to let some things go because when they made Portal, they weren't trying the save the world.

08-02-2011, 12:19 AM	#13
Dinosaur Rex Banned Join Date: May 2011 Reputation: 155 Posts: 1,424	It keeps it's momentum, just the direction of the forces changes, It's like making a hole through the earth, when you reach the center of the earth, the gravity force equals zero, but you can't just stop there, the energy is in there, so you come out at the same height you threw yourself into that hole but on the other side. If you are taking this to a theoretical level, make the equations.

08-07-2011, 02:42 PM	#14
rent-a-hero Join Date: Mar 2010 Reputation: 0 Posts: 33	momentum... ok, mass x velocity, a vector.... so, the question is: where or what is your referencial point? if its chell or one of the same pair of portals , i think momentum is conserved. always remenber, if in the future laws of physics do not apply, god help you.

08-07-2011, 05:56 PM	#15
alpha_centauri_ Join Date: Jul 2011 Reputation: 1 Posts: 43	Ummmm... I really don't think you guys understand... If you exit a portal not in the same direction you entered momentum is not conserved. I keep saying momentum is a vector... Please, nobody post anymore without reading what I said first and with a knowledge of physics. Again, I don't really care that the game made the mistake of saying "momentum" instead of "speed", but please stop saying that momentum is conserved. It isn't.