Heat is the transfer of energy from one body to another due to the difference in temperature between the two. A hotter object placed next to a cooler object will always transfer heat from itself into the cooler object, until both objects are of equal temperature. For example, when we place ice cubes in hot water, the heat from the hot water transfers to the ice cubes. This transfer of heat energy will continue until equilibrium is reached between the hot water and the ice.

Heat is a measure of the internal energy that has been absorbed or transferred from one body to another. It is not conserved; it can be either created or destroyed. There are two general ways that heating can occur: from a temperature difference, with energy moving from the region of higher temperature, and from an object gaining energy by way of an energy-form conversion.

The SI unit of heat is the joule. The metric unit of heat is called the calorie (cal), which is defined as the amount of heat required to raise the temperature of one gram of water from 14.5oC to 15.5oC. The English system’s measure of heating is called the British thermal unit (Btu), which is the amount of heat needed to increase the temperature of 1 pound of water 1 degree Fahrenheit.

Some examples of heat energy are: chemical energy from the foods is converted into heating our bodies; light from the sun is converted to heat as the sun’s rays warm the earth’s surface; energy from friction creates heat, like when we rub our hands; in light bulbs, electrical energy is converted into heat energy, etc.