4.+Energy+exists+in+many+forms

MAJOR UNDERSTANDINGS 4.1a The Sun is a major source of energy for Earth. Other sources of energy include nuclear and geothermal energy. 4.1b Fossil fuels contain stored solar energy and are considered nonrenewable resources. They are a major source of energy in the United States. Solar energy, wind, moving water, and biomass are some examples of renewable energy resources. 4.1c Most activities in everyday life involve one form of energy being transformed into another. 4.1d Different forms of energy include heat, light, electrical, mechanical, sound, nuclear, and chemical. Energy is transformed in many ways. 4.1e Energy can be considered to be either kinetic energy, which is the energy of motion, or potential energy, which depends on relative position. 4.2a Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature. 4.2b Heat can be transferred through matter by the collisions of atoms or molecules (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection). 4.2c During a phase change, heat energy is absorbed or released. Energy is absorbed when a solid changes to a liquid and when a liquid changes to a gas. Energy is released when a gas changes to a liquid and when a liquid changes to a solid. 4.2d Most substances expand when heated and contract when cooled. Water is an exception, expanding when changing to ice. 4.2e Temperature affects the solubility of some substances in water. 4.3a In chemical reactions, energy is transferred into or out of a system. Light, electricity, or mechanical motion may be involved in such transfers in addition to heat. 4.4a Different forms of electromagnetic energy have different wavelengths. Some examples of electromagnetic energy are microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. 4.4b Light passes through some materials, sometimes refracting in the process. Materials absorb and reflect light, and may transmit light. To see an object, light from that object, emitted by or reflected from it, must enter the eye. 4.4c Vibrations in materials set up wave-like disturbances that spread away from the source. Sound waves are an example. Vibrational waves move at different speeds in different materials. Sound cannot travel in a vacuum. 4.4d Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of energy. 4.4e Electrical circuits provide a means of transferring electrical energy. 4.4f Without touching them, material that has been electrically charged attracts uncharged material, and may either attract or repel other charged material. 4.4g Without direct contact, a magnet attracts certain materials and either attracts or repels other magnets. The attractive force of a magnet is greatest at its poles. 4.5a Energy cannot be created or destroyed, but only changed from one form into another. 4.5b Energy can change from one form to another, although in the process some energy is always converted to heat. Some systems transform energy with less loss of heat than others.