Heat Transfer

Heat is moved on the earth in three ways: Convection, Conduction and Radiation. In the convection method, when air is heated, molecules move around more. The more they move the more they collide and spread out. This causes a given area or space to have less and less pieces of air in it as the air heats up. Less pieces means less mass and we say that air becomes lighter as it gets hot. Cool air has more pieces per unit volume. Warm or hot air is lighter, so it rises above the cooler more dense, air.

In Conduction, as molecules heat up again they gain energy and move around. Molecules bang into other neighboring molecules and transfer the energy to them. This is how the handle of a pot, sitting on the stove, gets its heat.

In Radiation, The light from the sun, or other source travels through the air. Parts of the energy from the sun are called photons. These photons  are like small vibrating bullets that turn to heat when they hit something and are absorbed.  This energy is not always visible as light. Ultraviolet rays and X-Rays have photons that move even faster. This type of energy is the major source of heat on the earth.