Chapter 4: Energy 

Section 1: The Nature of Energy

  • What is energy?   * Every change that occurs—large or small—involves energy.   * When something is able to change its environment or itself, it has energy.   * Energy is the ability to cause change.   * Energy can be stored and it can move from place to place.   * Radiant energy from the Sun travels a vast distance through space to Earth, warming the planet and providing energy that enables green plants to grow.
  • Kinetic Energy: the energy a moving object has because of its motion.   * The kinetic energy of a moving object depends on the object’s mass and its speed.   * Joule: The SI unit of energy
  • Potential Energy: Stored energy due to position   * Energy doesn’t have to involve motion.   * Elastic Potential Energy: energy stored by something that can stretch or compress, such as a rubber band or spring.   * Chemical Potential Energy: Energy stored in chemical bonds   * Gravitational Potential Energy: energy stored by objects due to their position above Earth’s surface.   * According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground.   * An object’s gravitational potential energy increases as its height increases.

Section 2: Conservation of Energy

  • Changing Forms of Energy   * A lightbulb is a device that transforms electrical energy into light energy and thermal energy.   * Fuel stores energy in the form of chemical potential energy.   * In the engine of a car, several energy conversions occur.   * Some energy transformations are less obvious because they do not result in visible motion, sound, heat, or light.
  • Conversions Between Kinetic and Potential Energy   * To understand the energy conversions that occur, it is helpful to identify the mechanical energy of a system.   * Mechanical Energy: the total amount of potential and kinetic energy in a system and can be expressed by this equation.     * Mechanical energy is energy due to the position and the motion of an object or the objects in a system.   * Energy transformations also occur during projectile motion when an object moves in a curved path.   * Objects that can fall have gravitational potential energy.
  • The Law of Conservation of Energy: states that energy cannot be created or destroyed.   * Mechanical energy stays constant.   * Kinetic and potential energy simply change forms and no energy is destroyed.   * Energy can change from one form to another, but the total amount of energy never changes.   * The law of conservation of energy requires that the total amount of energy going into a hair dryer must equal the total amount of energy coming out of the hair dryer.     * The law of conservation of energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed.   * Sometimes it is hard to see the law of conservation of energy at work.   * The total amount of energy always stays the same.   * A special kind of energy conversion—nuclear fusion—takes place in the Sun and other stars.   * Mass is converted to energy in the processes of fusion and fission.   * Another process involving the nuclei of atoms, called nuclear fission, converts a small amount of mass into enormous quantities of energy.   * In either process, fusion or fission, mass is converted to energy.   * In processes involving nuclear fission and fusion, the total amount of energy is still conserved if the energy content of the masses involved are included.   * The process of nuclear fission is used by nuclear power plants to generate electrical energy.
  • The Human Body - Balancing the Energy Equation   * Some of the chemical potential energy stored in your body is used to maintain a nearly constant internal temperature.     * A portion of this energy also is converted to the excess heat that your body gives off to its surroundings.   * The complex chemical and physical processes going on in your body also obey the law of conservation of energy.   * Your body stores energy in the form of fat and other chemical compounds.   * To maintain a healthy weight, you must have a proper balance between energy contained in the food you eat and the energy your body uses.   * Your body also can use the chemical potential energy stored in fat for its energy needs.   * Every gram of fat a person consumes can supply 9 C of energy.

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