Yep - it's gotta be about momentum and total force and vectors and ...something...to do with magnets.

I kinda thought the handwave was that the frosted look (and vomiting) was because they didn't have the Earth 'gate tweaked quite right (with no DHD) and Sam didn't like throwing up or having frostbite on her nose so she fixed it (ie: it would get really old doing that EVERY episode)

Do you think their ears pop?

That should be a t-shirt or something - "I'm glad they conserve momentum" :)