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Let a balloon in the Space means space having no air or any external force, a balloon is filled with a higher energetic particles of gas, the structure of the balloon  is just like a Earth,particles of the gas in the balloon is applying the force on the wall of the balloon in every direction and with equal magnitude! (there is no any gravitational force)! tell me the status of the balloon means it will move up or down or right or left ?

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The key is in your first statement:  no external force!   Newton's 2nd law is F=mA so if F=0 then A=0 (the balloon and gas inside have mass not equal to 0).  So the balloon is definitely not accelerating.

Is the balloon moving?  Two possibilities exist:  If the balloon was initially moving and there are no external forces on the balloon then the balloon is still moving with a constant velocity.  If the balloon was initally at rest and there are no external forces then the balloon is still at rest.

What can be said of the balloon is that it is in equilibrium.

What goes on inside the balloon is immaterial because the internal gas is randomly hitting the balloon walls in every direction and with no unbalanced force on the balloon structure.

There are two ways to make the balloon move.  If an external force acts on the balloon it will accelerated and the balloon velocity will change.  The other way is to allow gas to escape from the balloon. The escaping gas creates a force on the balloon and accelerates it much like a rocket is propelled.




You did a great job in expressing all that is taking place in this scenario.  My assumption was that the gas would be released; therefore, creating a force on the balloon. 

Wishing you well,  Prasenjeet!

Hi Lori,
Thanks for the very positive comment about the balloon in space. We could have mentioned Brownian motion of the balloon's center of mass but I think that would have been over the top.
Best regards,

Your sentence, "Tell me the status of the balloon means it will move up or down or right or left,"  is a bit confusing. 

What do you mean by status, direction?    If you mean direction, then, up, down, right, ,or left would be relative. You need to have a point of reference. When the balloon releases the particles, it will use the wall most far from the release station to project, or move, the object. The relative direction could be determined by where that point of release is located, but you may still need to give a point of reference to set up a coordinate system.

Let me know if this was helpful.

What will happen here is that the balloon will expand in size. The net force (sum of forces on all points) exerted by the gas inside will be zero so that the balloon's motion will not accelerate in any direction. Here I assume the baloon is sphere-shaped.


One more detail:

The balloon will expand as long as the forces of the gas can overcome the baloon's surface tension. Most balloons will eventually pop in these conditions.