* Kinetic Energy: Heat causes the air molecules inside the balloon to move faster. This means they have more kinetic energy and collide with the balloon's inner walls more frequently and with more force.

* Pressure: The increased collisions create higher pressure inside the balloon.

* Expansion: The balloon expands to accommodate the increased pressure, resulting in a larger volume.

Think of it like this: imagine the air molecules as tiny bouncing balls. The hotter they get, the faster they bounce, pushing outwards against the balloon's walls and making it bigger.