Chapter 13- Energy 8 th Grade

Energy –The ability to do work or cause change. –Units? Joules (J) Power –The rate at which energy is transferred. Work –Transfer of energy from one object to another. –An object GAINS energy when work is done on it. 2 Basic Kinds of Energy –1) Kinetic –2) Potential

Kinetic Energy –Associated with motion Ex. Baseball being thrown through the air –Increases when both mass and velocity increase Ex. Bowling ball and golf ball

Potential Energy –Stored energy –A ball thrown into the air has its greatest potential energy as it reaches the highest point in its path. Potential Energy changing to Kinetic Energy –Ex. Niagara Falls –As water runs over the waterfall potential is converted to kinetic. 2 Types of Potential Energy –1) Gravitational Potential Energy –2) Elastic Potential Energy

Gravitational Potential Energy The more an object weighs, or the greater the object’s height, the greater its potential energy. The gravitational potential energy of a book on a shelf is equal to the work done to lift the book to the shelf.

Gravitational Potential Energy

Elastic Potential Energy Associated with objects that can be stretched or compressed. Ex. A compressed spring (Slinky) Ex. A pole-vaulter first converts kinetic energy into elastic potential energy.

Forms of Energy Mechanical Thermal Electrical Chemical Nuclear Electromagnetic

Forms of Energy Mechanical Energy –Associated with position and motion of an object. –Formula? Kinetic + Potential Thermal Energy –Total potential and kinetic energy of particles in an object. –In a machine, work output is less than input because some energy is converted into thermal energy. –Ex. An ice cube melts when its thermal energy increases. Electrical Energy –Energy of electric charges –Ex. Lightning

Forms of Energy Chemical Energy –In foods we eat –Released when fossil fuels are burned –Chemical potential energy is stored in fossil fuels. Nuclear Energy –Potential energy stored in nucleus of an atom –Ex. Nuclear power plants Electromagnetic Energy –Ex. Visible Light, sunlight, X-rays, radio waves

Energy Transformations Most forms of energy can be transformed into other forms. –Ex. Moving water to produce electricity. Single Transformations –Ex. When you rub your hands together on a cold day, you use friction to convert mechanical to thermal.

Single Transformations –Ex. Natural gas is used to heat water (chemical to thermal). –Ex. A light bulb converts electrical energy into electromagnetic energy.

Single Transformations Ex. An electric motor converts electrical energy to mechanical energy.

Energy Transformations Multiple Transformations Car engine- –Electrical energy produces a spark. –The thermal energy of the spark releases chemical energy in the fuel. –The fuel’s chemical energy in turn becomes thermal energy. –Thermal energy is converted to mechanical energy used to move the car and to electrical energy to produce more sparks.

Energy Transformations One of the most common energy transformations is the transformation between potential energy and kinetic energy As a pendulum swings, energy is continuously transformed between kinetic energy and potential energy.

Energy Transformations How is the kinetic and potential energies changing at position 2? Describe kinetic and potential Changing at position 4? Is the potential energy Changing at position 5?

Energy Transformations Where is the greatest potential energy? Where is the greatest kinetic energy? Where is the least potential energy? Where is the least kinetic energy?

Conservation of Energy States that when one form of energy is transformed to another, no energy is destroyed in the process. Energy cannot be created or destroyed. Albert Einstein –Suggested that energy can be created under certain conditions –Theory of Relativity –Energy alone is not conserved. However, since matter can be transformed to energy, scientists say matter and energy together are always conserved.

Energy and Fossil Fuels Fossil Fuels –Made from materials that formed hundreds of millions of years ago. –Coal, petroleum, and natural gas –Contain energy that came from the sun –When burned they released energy stored millions of years ago.

Energy and Fossil Fuels Combustion –The process of burning fuels During combustion, a fuel’s chemical energy is converted into thermal energy.

Turbines In coal-fired power plants, coal is burned to produce steam which is then used to turn a turbine. Turbines are connected to generators, when the turbines spin the generators produce electricity.

Turbines Spinning turbines have mechanical energy. (chemical, thermal, mechanical, electrical) This electrical energy is used to light your home and run electric devices.