balloon deflates
Gas molecules also exert pressure. Earths atmosphere exerts pressure because gravity acts on the huge number of gas particles contained in the atmosphere, holding it in place. Pressure is also exerted by a small sample of gas, such as that which is contained in a balloon. Gas pressure is the pressure that results from collisions of gas particles with an object. Inside the balloon, the gas particles collide with the balloons inner walls. It is those collisions which keep the balloon inflated. If the gas particles were to suddenly stop moving, the balloon would instantly deflate. The Figure below is an illustration of gas particles exerting pressure inside a container.