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What is energy? Slide 2 WHAT IS ENERGY? Energy is the ability to do work. Work is done when a force causes an object to move in the direction of the force. Work is a transfer of energy. Energy and work are expressed in units of joules (J). Slide 3 WHAT IS ENERGY? Slide 4 Kinetic Energy Kinetic energy is the energy of motion. All moving objects have kinetic energy. Kinetic Energy Depends on Mass and Speed If you know an objects mass (m) and its speed (v), you can calculate the objects kinetic energy with the following equation: kinetic energy mv 2 2 Slide 5 Potential Energy Potential energy is the energy an object has because of its position. Gravitational Potential Energy The amount of gravitational potential energy that an object has depends on its weight and its height. gravitational potential energy weight height Slide 6 Mechanical Energy Mechanical energy is the total energy of motion and position of an object. Both kinetic energy and potential energy are kinds of mechanical energy. The equation to find mechanical energy is: mechanical energy potential energy kinetic energy Slide 7 Mechanical Energy The mechanical energy of an object remains the same unless it transfers some energy to another object. But even if the mechanical energy of an object stays the same, the potential energy or kinetic energy can increase or decrease. Slide 8 Other Forms of Energy Thermal Energy is all of the kinetic energy due to random motion of the particles that make up an object. All matter is made up of particles that are always in random motion. So, all matter has thermal energy. Thermal energy increases as temperature increases and increases as the number of particles increases. Slide 9 Slide 10 Other Forms of Energy Chemical Energy is the energy of a chemical compound that changes as its atoms are rearranged. Chemical energy is a form of potential energy because it depends on the position and arrangement of the atoms in a compound. The energy in food is chemical energy. Slide 11 Other Forms of Energy Electrical Energy is the energy of moving electrons. Electrical energy can be thought of as potential energy that is used when you plug in an electrical appliance and use it. Sound Energy is caused by an objects vibrations. The objects vibrations transmit some kinetic energy to the air particles, which also vibrate. These vibrations transmit sound energy. Slide 12 Other Forms of Energy Light Energy is produced by the vibrations of electrically charged particles. Nuclear Energy is energy that comes from changes in the nucleus of an atom. Nuclear energy can be produced when nuclei are joined in a fusion reaction or when a nucleus is split apart in a fission reaction. Slide 13 Other Forms of Energy Solar energy: is the radiant light and heat from the Sun. It is a renewable energy. It is used as solar power to provide electrical generation. Geothermal energy: originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It is power extracted from heat stored in the Earth. Slide 14 Kinetic Energy and Potential Energy An energy conversion is a change from one form of energy to another. Any form of energy can change into any other form of energy. As the skateboarder on the next slide travels up and down the half-pipe, his energy changes back and forth between kinetic energy and potential energy. Slide 15 Slide 16 Kinetic Energy and Potential Energy Elastic Potential Energy Stretching a rubber band stores elastic potential energy in the rubber band. When you let the rubber band go, it goes back to its original shape. It releases its stored-up potential energy as it does so. Slide 17 Conversions Involving Chemical Energy Chemical energy is stored in the food you eat. Your body uses this chemical energy to function. Energy Conversion in Plants The chemical energy in the food you eat comes from the suns energy. Plants use photosynthesis to convert light energy into chemical energy, as shown on the next slide. Slide 18 Slide 19 Conversions Involving Chemical Energy The Process Continues Plants change light energy into chemical energy. The chemical energy in the food you eat is changed into another kind of chemical energy that your body can use. Your body then uses that energy to give you kinetic energy that you use in everything you do. Slide 20 Why Energy Conversions Are Important? Energy conversions are needed for everything we do. Heating our homes, getting energy from a meal, and many other things use energy conversions. Machines, such as a hair dryer, help harness energy and make that energy work for you. Slide 21 Why Energy Conversions Are Important? Conversions Involving Electrical Energy Some common energy conversions that involve electrical energy are shown in the table below. Alarm clock electrical energy light and sound energy Battery chemical energy electrical energy Light bulb electrical energy light and thermal energy Blender electrical energy kinetic and sound energy Slide 22 Energy and Machines A machine can make work easier by changing the size or direction (or both) of the force needed to do the work. Some machines allow you to use less force over a greater distance to do the same amount of work. Machines as Energy Converters Some machines help you use energy by converting it into the form of energy that you need. Slide 23