<P> Air pressure, technically, is a measurement of the amount of collisions against a surface at any time . In the case of balloon, it's supposed to measure how many particles at any in any given time space collide with the wall of the balloon and bounce off . However, since this is near impossible to measure, air pressure seems to be easier described as density . The similarity comes from the idea that when there are more molecules in the same space, more of them will be heading towards a collision course with the wall . </P> <P> The first concept of air pressure within a balloon that is necessary to know is that air pressures "try" to even out . With all the bouncing against the balloon wall (both interior and exterior) there will be a certain amount of expansion / contraction . As air pressure itself is a description of the total forces against an object, each of these forces, on the outside of the balloon, causes the balloon to contract a tiny bit, while the inside forces cause the balloon to expand . With this knowledge, one would immediately assume that a balloon with high air pressure inside would expand based on the high amount of internal forces, and vice versa . This would make the inside and outside air pressures equal . </P> <P> However, balloons have a certain elasticity to them that needs to be taken into account . The act of stretching a balloon fills it with potential energy . When it is released, the potential energy is converted to kinetic energy and the balloon snaps back into its original position, though perhaps a little stretched out . When a balloon is filled with air, the balloon is being stretched . While the elasticity of the balloon causes tension that would have the balloon collapse, it is also being pushed back out by the constant bouncing of the internal air molecules . The internal air has to exert force not only to counteract the external air to keep the air pressures "even", but it also has to counteract the natural contraction of the balloon . Therefore, it requires more air pressure (or force) than the air outside the balloon wall . Because of this, when helium balloons are left and they float higher, as atmospheric pressure decreases, the air inside it exerts more pressure than outside it so the balloon pops from tension . In some cases, the helium leaks out from pores and the balloon deflates, falling down . </P>

How to do a balloon in a balloon