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I am wanting to start building a portal 2 map for single player mode.

I have used the hammer world editor before but not for portal.

As far as portals are concerned will the distance I drop vertically be equal to the distance I am thrown horizontally?

So a 16 unit drop throws me 16 units forward?

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It doesn't work like that at all. Look into the physics of velocity and acceleration. Falling vertically accelerates you until you hit the portal at which point you're at a certain speed, then you're flung out of a horizontal portal at that speed. That could potentially carry you very, VERY far forward - you'd only stop when wind drag brings you to a halt, or when you hit the ground. – doppelgreener Oct 1 '11 at 4:56
Google projectile motion. – Amplify91 Oct 1 '11 at 18:46
Do note, however, that Portal has a terminal velocity. See Here – Raven Dreamer Nov 11 '12 at 21:32

Portal does not model Air Resistance (this is why you can alternate between two ground-based portals indefinitely, without losing height), though there does appear to be a terminal velocity.

But below that terminal velocity threshold, vertical distance remains the same -- fall 16 units, get shot up 16 units*.

*Assuming both portals are on the ground.

If you're mixing horizontal and vertical portals (or 45* angle portals), the distance will not be the same; as Jonathan Hobbs mentions in the comments, projectile motion comes into play, and you will go less high if your exit portal is at 45*, and less far if your exit portal is vertical (unless you also have room to fall downwards at the same time; hitting the ground cancels your momentum immediately).

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It depends on how high above the ground you exit the portal. If you exit at ground level you're not going to go far at all. If you exit well above ground level you could move horizontally much further. Like the comments say though, looking into projectile motion will help too.

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