Density Decreases
* Density is mass divided by volume: Density = Mass / Volume
* Mass stays the same: The amount of helium inside the balloon doesn't change when it expands.
* Volume increases: As the balloon rises, the lower air pressure allows the helium to expand.
* Since the mass remains constant and the volume doubles, the density is halved.
In simpler terms: Imagine you have a fixed amount of helium squeezed into a small space. When the balloon expands, you're spreading that same amount of helium over a larger area, making the helium less concentrated (less dense).
