When an inflated balloon is released with its end unsealed and takes off across

Question

When an inflated balloon is released with its end unsealed and takes off across the room, how is momentum conserved? Momentum is conserved because the air molecules inside the balloon are moving out in the opposite direction from the balloon's movement. Momentum is conserved because the balloon is displacing atmosphere molecules from the air around it. Momentum is conserved because the balloon is getting smaller. Momentum is conserved because the balloon is getting larger. Momentum is conserved because the air from the balloon pushes the air behind it.

Explanation / Answer

Momentum is conserved because the airmolecules inside the balloon are moving out in the opposite direction from the balloon's movement.

REASON

It is a result of Newton's 3rd law of motion - for every action, there is an equal and opposite reaction along the same line. The air rushes out of the balloon, and the balloon goes in the opposite direction and it pushes against the released air.

In more detail, 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.

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