Naima is standing at the base of a hill holding a balloon filled with air, and Keiji stands at the top of the same hill holding an identical balloon. Both balloons are exposed to the same sunlight and atmospheric conditions, except for the difference in altitude. What happens to the balloons as time passes, considering the change in atmospheric pressure from the base to the top of the hill, and what might Naima and Keiji observe regarding their balloons? Respond very briefly.
As time passes, Naima, who is standing at the base of the hill, will observe that her balloon stays about the same size, while Keiji, at the top of the hill, might notice that his balloon has slightly expanded. This is because atmospheric pressure decreases with altitude. At the top of the hill, the lower external pressure around the balloon allows the air inside Keiji's balloon to expand outward more than it does in Naima's balloon at the bottom of the hill, where atmospheric pressure is higher and pushes harder against the balloon's surface, keeping it from expanding as much.