1. Energy is the ability to do work. 2. The SI unit of measurement for energy is the joule (J). 3. The sun is Earth’s primary source of energy. 4. Green plants trap some of the sun’s energy in a process called photosynthesis. 5. All types of energy fall into two main groups: kinetic energy and potential energy. 6. Kinetic energy is the energy of movement. 7. Forms of kinetic energy: motion energy, heat energy, electrical energy, sound energy and light energy.
8. Potential energy is stored energy. 9. Forms of potential energy: gravitational potential energy, elastic potential energy, chemical energy and nuclear energy.
10. The law of conservation of energy states that energy cannot be created or destroyed, it can only change from one form to another.
11. Energy can change from one form to another to perform a function, e.g. an electric light bulb: energy input = electrical energy; energy output = light and heat energy.
12. In an energy conversion some energy is changed into useful forms and some is dissipated.
13. The efficiency of a device is determined by how much of the input energy is changed into useful output energy.
14. Calculating efficiency:
Useful energy output (J) x 100 Total energy input (J)
= % Efficiency
15. Appliances have energy efficiency ratings. This tells us how efficient the appliance is. A is the most energy efficient. G is the least energy efficient.
16. The energy efficiency of a device may be improved by reducing friction and heat loss.
17. Houses for sale or lease must have a Building Energy Rating (BER) certificate. This tells us how energy efficient a house is. An A rating means the house is very energy efficient. G means the energy efficiency of the house is poor.
Questions and Exercises K C
Key Concepts Rewrite the following sentences in your copybook and fill in the blanks. 1. Energy is the ability to do ___________. 2. Energy is measured in ___________. The symbol for this unit is ___________. 3. The sun can be described as the earth’s ___________ source of energy. 4. Green ___________ trap some of the sun’s energy in a process called ___________.
