2. Energy transformations.

• A battery contains chemical energy which is transformed into electrical energy (electric current). Then a lightbulb transforms the electrical current into luminous and thermal energy.
• The chemical energy in our muscles can be transformed into mechanical energy in order to move objects.
• Chemical energy can be stored in fireworks. When fireworks explode, that chemical energy is coverted into light, heat, sound and mechanical energy.
• Photovoltaic solar panels tranform luminous energy from the Sun into electrical energy.
• A kitchen mixer converts electrical energy into kinetic energy to turn the machine's axis.
• Internal combustion engines transform the chemical energy of fossil fuels into thermal energy. Most of this thermal energy is transformed into motion, but some is lost as heat. Some energy is also lost as sound when certain parts of the motor hit each other and vibrate.
• In stars, the nuclear energy of atoms, such as hydrogen, is transformed into very intense luminous and thermal energy. 

Energy can be transformed, but it cannot be created or destroyed. This is the principle of energy conservation.