5.2 ENERGY SOURCES 103 The use of the word energy dates all the way back to the 4th century BC. It comes from the Greek energeia, meaning activity. Developed by Aristotle, enérgeia has no direct translation to English. It is frequently described as being at work . The word energy refers to the capacity or power to do work, such as the capacity to move an object of a given mass by the application of force. Go online and find some information about the history of the word energy. ONLINE RESOURCES Energy problems TYPES OF ENERGY There are many different types of energy , but they all fall into two primary categories: Kinetic: the energy of a moving object; Potential: energy that is stored in an object or substance. Energy sources are forms of potential energy that can be used to perform work. Potential energy Kinetic energy Chemical energy is energy stored in the bonds of atoms and molecules. Batteries, biomass, petroleum, natural gas, and coal are examples of chemical energy. Mechanical energy is energy stored in objects by tension. Compressed springs and stretched rubber bands are examples of stored mechanical energy. Nuclear energy is energy stored in the nucleus of an atom, the energy that holds the nucleus together. Large amounts of energy can be released when the nuclei are combined or split apart. Gravitational energy is energy stored in an object s height. The higher and heavier the object, the more gravitational energy is stored. Hydropower is an example of gravitational energy, where gravity forces water down through a hydroelectric turbine to produce electricity. Radiant energy is electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays, and radio waves. Sunshine is radiant energy, which provides the fuel and warmth that make life on Earth possible. Thermal energy, or heat, is the energy that comes from the movement of atoms and molecules in a substance. Heat increases proportionally to the speed of the moving particles. Geothermal energy is the thermal energy in the Earth. Kinetic energy is energy stored in the movement of objects. The faster they move, the more energy is stored. Wind is an example of motion energy. Sound is the movement of energy through substances in longitudinal waves. Sound is produced when a force causes an object or substance to vibrate. Electrical energy is delivered by tiny charged particles called electrons, usually moving through a wire. plug: presa di corrente to release: rilasciare rubber band: elastico to split apart: dividere spring: molla Energy conservation Energy can be transferred or transformed but the total amount of energy does not change: this is called energy conservation. In fact the law of conservation of energy states that energy can be transferred or transformed, but can never be destroyed or created. This is known as energy conversion and, more precisely: transfer refers to the movement of energy from one location to another. For example, when electricity moves from a wall plug, through a charger, to a battery; transformation occurs when energy changes from one form to another, like when a hydroelectric dam transforms the kinetic energy of water into electrical energy. 226 Think green MechPower.indb 226 30/01/24 17:09