Heat Transfer

Three Methods of Heat Transfer Heat always goes from hot to cold. Heat is movement of energy from a warmer object to a cooler object.

Radiation Heat transfer by radiation takes place with no direct contact between a heat source of an object. Will transfer through the vacuum of space. Matter is not required. Other familiar forms of radiation include the heat you feel around a flame or open fire. Radiation enables sunlight to warm Earth’s surface.                                See full-size image.

Conduction What happens as a spoon heats up in a pot of soup? The heat is transported from the hot soup and the pot to the particles in the spoon. The particles near the bottom of the spoon vibrates faster as they are heated, so they bump into other particles as they travel through the handle of the spoon and pot. Soon the handle will be too hot to hold! Usually associated with solids.

Convection Conduction heats up the spoon, but how does the soup inside the pot heat up? Heat transfer involving the movement of fluids- liquids and gases- it is called convection. During convection, heat particles of fluids begin to flow transferring heat energy from one part of the fluid to another.

Convection and Density The warmer particles are moving faster, they spread out more. So they are less dense and rise. After giving their energy to the cooler fluid at the top, they are now cooler and more dense. More dense fluids sink.

Convection Currents Diagram

Convection Currents The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to place the currents in motion. Convection currents continue as long as heat is added without heat the currents will stop when all of the material has reached the same temperature. However, heat from the Earth’s mantle and core causes the currents to form in the asthenosphere.

Key Terms! Heat Transfer- The movement of energy from a warmer object to a cooler object. Radiation- The direct transfer of energy through empty space by electromagnetic waves. Conduction- The transfer of heat from one substance to another by direct contact of particles of matter. Convection- The transfer of heat by movements of a fluid. Density- The amount in a given space; mass per unit volume. Convection Currents- The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another.