times moving in a direction away from the open stem.
The balloon moves because of an unbalanced condition existing
within it. The jet of air does not have to push against the outside
atmosphere; it would function better in a vacuum. When the stem area
of the balloon is released, a convergent nozzle is created. As the
air flows through this area, velocity is increased accompanied by a
decrease in air pressure. In addition, an area of skin against which
the internal forces had been pushing is removed. On the opposite
internal surface of the balloon, an equal area of skin still remains.
The higher internal pressure acting on this area moves the balloon in
a direction away from the open stem. The flight of the balloon will
be of short duration, though, because the air in the balloon is soon
gone. If a source of pressurized air were provided, it would be
possible to sustain flight of the balloon.
If the balloon were converted into a length of pipe, and at
the forward end an air compressor designed with blades somewhat like
a fan were installed, this could provide a means to replenish the air
supply within the balloon.