Uh... sorry I don't know where I can ask this (I'm new at this) but... can someone explain me about momentum? Thank you :)

Momentum is a Portal game mechanic that involves players to redirect their speed in one direction to another. One example: the exit is on the other side of the map on an elevated plataform without portal surfaces. The side in which the player is has a portal surface above the height of the exit plataform and a hole which has a portal surface on the bottom floor of it. The solution would require momentum: placing the blue portal on the hole, the other on the portal surface on the player's side and jump on the hole.

Also, I think this topic should be on Hammer and Modding.