Hiểu theo nghĩa thông thường, năng lượng là khả năng làm thay đổi trạng thái hoặc thực hiện công năng lên một hệ vật chất. | 10 energy a beginner s guide height above ground h and the gravitational constant g Ep mgh. Springs that have been tensioned by winding are a common example of the practical use of elastic potential energy that is stored due to their deformation and released as useful work as the coil unwinds and powers a watch or a walking toy. Biomass living in plants micro-organisms animals and people and dead mainly in soil organic matter and tree trunks and fossil fuels formed by the transformation of dead biomass are enormous stores of chemical energy. This energy is held in the atomic bonds of tissues and fuels and released through combustion rapid oxidation which produces heat an exothermic reaction . This results in new chemical bonds the formation of carbon dioxide frequently the emission of nitrogen and often sulfur oxides and in the case of liquid and gaseous fuels the production of water. HEAT Heat of combustion or specific energy is the difference between the energy of the bonds in the initial reactants and that in the bonds in the newly-formed compounds. The poorest fuels wet peat wet straw release less than a third of the thermal energy produced by burning gasoline or kerosene. The energy content of a fuel foodstuff or any other combustible material can easily be determined by burning an absolutely dry sample of it in a calorimeter a device that measure the heat given off during chemical reactions . Heat is produced by a number of other energy conversions nuclear fission is a major commercial process whose heat is used to generate electricity heat arising due to the resistance to the flow of electric current is used to prepare food boil water and warm interior spaces and friction produces a great deal of unwanted inside vehicle transmissions as well as unavoidable between vehicle tires and road heat. Once produced heat can be transferred in three ways conduction that is direct molecular contact most commonly in solids convection by moving liquids or gases and .
