The Real Doctor wrote:
It amazes and depresses me how prevalent the nonsensical believe that
"gravity powers gliders" extends in the gliding world.

We all owe you a debt of gratitude for showing us how ignorant we are.

Cars won't be able to work either, since no gravity = no weight = no
friction at the tyres. Would you say that gravity powers cars?

I think pedantic trolling powers cars:
http://blog.modernmechanix.com/2008/...-makes-85-mph/

I don't really go in for arguments from authority, but

I removed the contradiction in order to protect small children.