Can you explain why an inflated balloon shoots off when air is released?

Answer 1

The air inside the balloon is at a higher pressure than atmospheric pressure so the gas molecules inside the balloon are closer together on average than gas molecules outside the balloon. This means that the repulsive forces between the gas molecules inside the balloon are greater than the repulsive forces between the gas molecules outside it. When the balloon is opened, the gas molecules in the open end at the border between the higher pressure interior and lower pressure exterior will experience a greater repulsive force from the gas molecules inside the balloon than the molecules on the outside. This means that they experience a net force pushing them out of the balloon. As these gas molecules are pushed out by the gas inside the balloon, they push back on it with an equal and opposite force (due to Newton's 3rd Law of Motion). This equal and opposite reaction force causes the gas in the balloon to be pushed in the opposite direction to the escaping gas, which in turn pushes the balloon. As more and more gas escapes, the reaction force on the balloon continues to accelerate it, making it shoot off, until enough gas has escaped for the pressure inside the balloon to have dropped to the same level as the pressure outside the balloon.