* Air Pressure: Air pressure decreases as you go higher in altitude. Think of it like fewer molecules pushing down on you.
* Balloon's Response: The balloon is filled with air. When the surrounding air pressure drops, the pressure inside the balloon becomes relatively higher. This pressure difference causes the balloon to expand until the internal and external pressures are more balanced.
In simpler terms: Imagine the balloon as a tiny, flexible container. As you climb higher, the air pressure outside the container gets weaker. This allows the air inside the balloon to push outward more easily, making it bigger.
