* Kinetic Energy: Heat is a form of energy. When you add heat to air, you increase the kinetic energy of the air molecules. This means they move faster and collide more frequently.

* Expansion: The increased movement of air molecules causes them to spread out and occupy more space. This results in an increase in the air's volume.

* Charles's Law: This fundamental gas law states that the volume of a gas is directly proportional to its absolute temperature (measured in Kelvin) when pressure is held constant. So, as temperature goes up, volume goes up proportionally.

Example: Think of a hot air balloon. The air inside the balloon is heated, causing it to expand. This expansion makes the air inside less dense than the surrounding air, which creates buoyancy and allows the balloon to rise.