# Ideal Gas Law

### The Recipe for Weather: The Ideal Gas Law

When you inflate a balloon, the air molecules inside the balloon get packed more closely together than air molecules outside the balloon. This means the density of air is high inside the balloon. When density of air is high, the air pressure is high. The pressure of the air pushes on the balloon from the inside, causing it to inflate.  If you heat the balloon up, the air pressure gets even higher.

Air pressure depends on the temperature of the air and the density of the air molecules.

Atmospheric scientists use math equations to describe how pressure, temperature, density and volume are related to each other. They call these equations the Ideal Gas Law. This equation helps us explain how weather works, such as what happens in the atmosphere to create warm and cold fronts and storms, such as thunderstorms. For example, if air pressure increases, the temperature must increase. And If air pressure decreases, the temperature decreases. It also explains why air gets colder at higher altitudes, where pressure is lower.

Note: In this equation, the temperature (T) is measured in the unit of kelvin (K).

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