Conduction is the transfer of heat through direct contact between two objects. Convection is the transfer of heat through the movement of a fluid, such as air or water. Radiation is the transfer of heat through electromagnetic waves.
Convection currents occur when a fluid is heated, causing it to expand and become less dense. The less dense fluid then rises, while the cooler, denser fluid sinks. This creates a continuous circular flow of fluid, transferring heat from one area to another.
Metals are good conductors of heat, while materials such as wood, plastic, and air are good insulators. This is because metals have loosely bound electrons that can easily transfer heat, while insulators have tightly bound electrons that do not allow heat to pass through easily.
Radiation can both heat and cool objects. When an object absorbs radiation, its temperature increases. When it emits radiation, its temperature decreases. This is why objects can feel hot or cold when exposed to different sources of radiation, such as the sun or a fire.
Heat is transferred in the Earth's atmosphere through a combination of conduction, convection, and radiation. The sun's radiation heats up the Earth's surface, which then creates convection currents in the air. These currents transfer heat through the atmosphere, while some heat is also transferred through conduction between the surface and the air above it.