How do you explain why air rises as it is heated?

Substances that have internal movement(gas, liquid, and solids to a certain degree) will have convection currents. The concept is most easily understood in a gas. As gases are heated their molecules travels faster and faster. The faster they move and the more the kinetic energy involved in the collisions causes the gas to increase in volume. This means that the particles are further apart and therefore the density of the gas decreases. And substances with lower density will rise. This can also be thought of as kinetic and potential energies. As the gas is heated the molecules inside have increased kinetic energy. The increased energy of the molecules allows the molecule to reach higher potential energy levels(which means the molecule can rise).

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