Hot air balloon

Today, I was watching the move "Up", and I was mindful of how a hot air balloon works.  The reason why it is able to move up and take people along for the ride is because of the hot air that is applied to the inside of the balloon (it is also known as the "envelope").  The hot air makes it buoyant because it makes it have a lower density than the colder air around it, (warmer air rises over colder air). The balloon doesn't have to be closed at the bottom because the air at the bottom of it has the same pressure as the surrounding air.

The balloon can be manipulated to move up and down.  To make it rise, the hot flame is opened (the bigger the flame, the faster it moves up).  To make it come down, a "valve" at the top of the envelope is opened to release the hot air inside the balloon, making it descend.