Heat energy is obtained from chemical energy by combustion, e.g. by burning a fuel such as coal, gas, kerosene, etc. It is also obtained by radiation when infrared rays strike an object, e.g. radiation from the sun, electric heating elements, etc. Heat generally causes expansion and can be used up to do work. In a car, for example, a compressed mixture of air and petrol is ignited by a spark, causing an explosion.
The heat generated does work in pushing the piston whose movement is responsible for the motion of the car. Thus, chemical energy is converted into kinetic energy, which, in turn, is converted into kinetic energy. In the Bunsen burner, petroleum gas is burnt to produce heat energy. Heat rays, which are infrared, are electromagnetic waves, which travel with the velocity of light.