Time to Think With Portals

[White Rabbit]

Not in-game without the sv_allow_mobile_portals cheat, but the red portal in the picture (apparently finding orange in Paint is too hard) is on a panel moving downwards.
Someone tested it, but the Source engine had difficulties: http://forums.steampowered.com/forums/show...41#post22516541

[LANS]

QUOTE (White Rabbit @ May 20 2011, 02:01 PM) Interesting drawing: http://lastopp.no/3/85598fa1714fb80014d1d7c1d04fb2fb.jpg
I don't think even think a meaningful answer is possible. What would happen if the cube is a tall column and there's a low ceiling above the blue portal, and the column smashes against the ceiling? Where's the kinetic energy really coming from?

I found the picture on the Steam forums: http://forums.steampowered.com/forums/show...d.php?t=1897716

Depends if the momentum of the object is considered relative to the portal, or relative to the game corrdinate's origin system. If portal, it goes flying. If coordinate origin, it doesn't move very far.

[Makida]

Edit: At first I thought it was A., because the portal itself isn't a "thing," and the cube is stationary relative to both the platform it starts on and the blue portal's platform; so it seems all that'd happen is the cube would suddenly find itself sitting on a slanted platform rather than a stationary one. Then I thought maybe it's B., because looking up through the orange portal, the cube does have velocity relative to the blue portal's platform. After all, we know portals change the velocities of objects entering and exiting them; if two portals are turned at 90 degree angles to each other, an object entering one would upon exiting the other suddenly be moving with a velocity of 0 along its original vector, and would instantly gain velocity along a different one.

Actually now I think it's B. If you imagine actually looking at what happens to the cube, it's clear it will be emerging from the blue portal very rapidly, just as rapidly as the orange portals' platform is moving; at first only the cube's top would appear from the blue portal, then, only a split-second later, the rest of it... In other words, relative to the blue portal's platform, the cube will be moving very quickly upon its exit from the portal. Since there's nothing to stop it, it will keep moving quickly, and fly off the platform.

Edit: No, wait, it's A. At first the cube will seem to be moving rapidly, but that's only because it's emerging from the blue portal at the same rate as it's being engulfed by the orange portal. As soon as the orange portal stops moving, once the pad it's on hits the cube's original resting place, the cube will stop emerging; there will be nothing acting on it to make it keep moving at that point. Its momentum would be just an illusion. It wouldn't really exist relative to any object in the scenario except for the pad on which the orange platform is located, and that will never come in contact with the cube, and will stop moving relative to it as soon as it hits the cube's first platform.

Edit: No, no, it's B. From the perspective of the blue portal, what's happening is the cube is being pushed upwards through it by a rapidly moving piston (i.e. the platform it's originally resting on). There's nothing to make the cube suddenly stop just because the "piston" pushing it stops; it will still have momentum, and will be a speedy thing...

Maybe this confusion is why moving portals don't work well in the games. Someone build a real-life wormhole so we can test it out...

[Bard]

Hrm. I wonder if I can put a portal on the front of a Half-Life 2 Train?.

[White Rabbit]

Video here: http://www.youtube.com/watch?v=S85nudR6D-Y
Testing commences at 0:50.

Older video here: http://www.youtube.com/watch?v=S1AIR6m8uLk...feature=related