Momentum, a function of mass and velocity, is conserved between portals. In layman's terms, speedy thing goes in, speedy thing comes out.

Do you think I'm trying to trick you with reverse psychology? I mean, seriously, now.

Your entire life has been a mathematical error... a mathematical error I'm about to correct!

Time out for a second. That wasn't supposed to happen. Do you see that thing that fell out of me? What is that? It's not the surprise. I've never seen it before! Never mind, it's a mystery I'll solve later... by myself, because you'll be dead.

Remember, the Aperture Science Bring Your Daughter to Work Day is the perfect time to have her tested.