Question

if a ballon filled with air and its mouth untied is released with its mouth in the downward direction it moves upwards why

Answer 1

The pressure inside the ballon is greater than the pressure outside the balloon. The pressure wants to equalize, so when the mouth of the balloon is opened, air rushes out the hole. Since the hole has a narrow aperture and the pressure inside is high, this produces sufficient thrust to move the very light balloon in the opposite direction of the escaping air

Answer 2

Explanation:

If the inflated balloon is released with its mouth untied in the downward direction, then it will move upwards because the air rushes out of balloon in the downward direction. The equal and opposite reaction of downward thrust of air pushes the balloon upwards.