Conduction takes place most readliy in solids, but also takes place in liquids and gases. An example would be the heat that moves up an iron rod that is held in a fire. Convection is the movement of heat by a moving medium. Convection takes place only in liquids and gases since solids do not flow. The movement of the forced hot air of a furnace is an example of convection.
Radiation is the movement of heat by an invisible ray.
The heat that comes from the rays of sun is an example or radiation. The BTU is the amount of heat that will raise the temperature of 1 pound of water 1 degree Fahrenheit. If you compress a gas, it creates heat. A gas is made up of small particles, which have a vibrational energy. This heat is called the heat of compression.