In this topic you will learn about how heat energy moves from one location to another.
The energy of any moving object is called kinetic energy. Energy cannot be created or destroyed. It can only be changed from one form to another. A speeding roller coaster has a great deal of kinetic energy as it reaches the bottom of the first hill. The kinetic energy cannot disappear when it reaches the bottom of the hill. It changes to a new form called potential energy. Potential energy is defined as the energy stored in an object or a material.
Molecules in a material move around at different speeds. Taken together they have an average speed. The average speed of the molecules in a material determines the molecules' average kinetic energy. Temperature is a measure of the average kinetic energy of the molecules in a material.
Energy always flows from the hotter object to the cooler one. Energy will continue to flow until the two objects reach the same temperature. The energy that flows between objects that have different temperatures is called heat.
Heat can move. The transfer of energy by electromagnetic waves is called radiation. Objects near room temperature give off mainly infrared radiation, which our eyes cannot see. When objects are heated to about 600°C, they begin to give off visible light.
The spread of molecular motion between areas of different temperatures that are in contact is called conduction. Conduction is the only way heat can travel through solids. Another type of heat transfer, called convection, can occur in liquids and gases. Convection is the transfer of energy by the flow of a liquid or a gas. In the atmosphere, warmer air carries heat upward. The warm air rises because of its lower density. Cooler air is denser and sinks.
Insulation prevents heat from flowing in or out of a material. A material can be insulated by wrapping it securely with something that is not a good conductor of heat. Air is a very poor conductor of heat and is therefore a good insulator.