I just need to know about the physics behind a balloon powered car and how its made?
First define a ballon powered car :-)
I can think of many ways a car could be powered by a ballon from escaping air pressure to a big bloke called "ballon" peddling.
Hi Bevis, welcome.
I've got a link in ahead of Orac!!!
If this doesn't answer your question, there is plenty of hot air about on this forum at the moment that might help.
www.wikihow.com/Make-a-Balloon-Car