How would I make it so players don't loose momentum when jumping or falling?

Right now, Roblox has it so when a player is in a falling or jumping state, all their momentum was lost. This becomes an issue if your game involves quickly moving parts, meaning players could move off easily. In real life, when you jump, you stay parallel to the surface you jumped off from. Obviously, this excludes air friction, but how could I have it so that players keep their momentum when jumping or falling?