In Portal, the player controls the protagonist, Chell, from a first-person perspective as she is challenged to navigate through a series of rooms using the Aperture Science Handheld Portal Device (portal gun or ASHPD). The portal gun can create two distinct portal ends, orange and blue. The portals create a visual and physical connection between two different locations in three-dimensional space. Neither end is specifically an entrance or exit; all objects that travel through one portal will exit through the other. An important aspect of the game's physics is momentum redirection. As moving objects pass through portals, they come through the exit portal at the same direction as the exit portal is facing and with the same speed with which they passed through the entrance portal.