# Portal Physics 211

In the Aperature Labs testing course there are no enemies, nor any weapons. There are however walls you cannot climb, chasms you cannot cross, and doors you cannot access. So you may be wondering by now, "How the heck am I supposed to get through the course then?? That's impossible". Thanks to the innovations here at Aperature Science Labs, we have made the impossible, easy. Our latest product is currently in the testing phase right now, and you our one of the privileged few that get to experience tomorrow, today; with the Aperture Science Handheld Portal Device, or as some have called it, the Portal Gun. Using the Portal Gun, the user can create a stable inter-spacial wormhole for travel over short distances. Using these portals, the user is able to transport themselves instantly from one portal end to the other, makes otherwise difficult travel, easy.

#### IMAGE SOURCE: http://en.wikipedia.org/wiki/File:Portal_physics-2.svg

We can see from the above image just how movenment through a protal works. You may have an final velocty of J before entering the blue portal. When you exit the orange one, you are still moving with that velocity. However, now that you are height H above the ground, you now have a potential energy. Since there are no obstacles all that pontential energy is transformed into kinetic energy, also known as movement. The game makes use of this to help propel players across great distances. The higher the ledge we jump off of, into a portal below, the greater or entering velocity is, and we then exit the other portal with that same velocity, but a new direction. The "destination" portal, the one we are jumping to, can be moved, mid air, so players can use this to their advantage to move their next "out" portal to a higher ledge, or the like.

#### IMAGE SOURCE: http://www.wired.com/images/article/magazine/1510/pl_games1_630.jpg

We can use this same mechanic with both portals being shot onto "floor" surfaces. By doing this, we can gain height by using our velocity gained by gravity to propel us high enough to shoot a portal onto a higher ledge. We can repeat this process over and over to traverse a room where there are only pedestals of differing, but increasing height. In pretty much all of these cases we in essence gain "free" potential energy. There was no work done to get up to our new height, the portal just took us there instantaneously. As the game progresses along, each level becomes longer where the player eventually has to start using all of the techniques they have learned. They will use gravity to gain velocity so that they can then be should horizontally like a projectile. Since the physics of the game are modelled (almost) exactly like the real world, players quickly learn the rules.

#### IMAGE SOURCE: freeze frame of youtube video below.

The video shown below is an "orientation" video for the game. In it, it demonstrates the many uses of the "portal gun". In it, we see a short glimpse of a diagram for "skydiving". Since we can essential gain free kinetic energy, we can place two portals one directly above the other. If we move into this path, we start to fall contiously. While we will gain velocity initially, eventually the drag force pushing up on us equals that of gravity pulling us downward. At that point we reach our terminal velocity. While not useful in the game at all, it does unlock an acheivment.