Maglev is a much talked about technology that uses the simple theory of physics that opposite poles of magnets repel. Maglev vehicles use superconductive magnets to propel and support a train above a track. Trains can be made to travel extremely fast on these tracks because the train doesn't come into contact with the track, therefore there is no friction, and the main barrier to even higher speeds is air resistence. Trials began on a maglev train track in Japan in the 70's and a speed of 500kph has been attained. The train is levitated by electromagnets and forward thrust is provided by linear motors aboard the cars. A small low power maglev system is in use at Birmingham Airport, England. In Osaka, Japan there is a subway line which uses maglev carriges.