physics train

hey thanks to everyone who posted in my corkscrew train topic, but i have another problem now. Here is a post from that thread that i have a question about:

<DIV class=forumtext>Surely with the HL2 uberPhysics (TM), you can make a real constraints based rollercoaster. You should be able to make something that is attatched to a track with a low friction linkage, then winch it up to a height, and let it slide down a track of whatever path you like? </DIV>
<DIV class=forumtext> </DIV>
<DIV class=forumtext>I just purchased HL2 and have started with the SDK, and i am very confused. If someone would tell me how to make such a train in the new hammer (one that would use real physics somehow) i would greatly appreciate it</DIV>

This is something I think you're probably going to have to figure out on your own bud. It's not one of those standard things we can just whip out an easy answer to. Read all the physics tutorials you can find, and do lots of experimentation. If it's possible, I'm sure you'll figure something out.

mkay ill look, if i figure it out ill post an answer