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Chapter 4-- Energy

Chapter 4-- Energy. The Nature of Energy. What is Energy — Energy is present all around us all day Energy changes are taking place constantly Ex: baseball flying and hitting a window, combing your hair, walking to class, etc. Energy is the ability to cause change

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Chapter 4-- Energy

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  1. Chapter 4-- Energy

  2. The Nature of Energy • What is Energy— • Energy is present all around us all day • Energy changes are taking place constantly • Ex: baseball flying and hitting a window, combing your hair, walking to class, etc

  3. Energy is the ability to cause change • Anything that causes change must have energy • There are many different forms of energy including electrical, chemical and thermal

  4. Kinetic Energy • -is energy in the form of motion • Ex: spinning wheel, sprinting runner, football passing through goalposts • Amounts of Kinetic Energy depend on two quantities: mass and velocity • (more mass = more energy) • (more velocity = more energy)

  5. Potential energy • -is stored energy due to position • Objects that have potential energy have the ability to cause change • Elastic Potential Energy= energy stored by something that can stretch or compress (ex: rubber band) • Chemical Potential Energy = energy stored in chemical bonds (ex: atoms)

  6. Gravitational Potential Energy (GPE) • Gravitational Potential Energy is energy stored by objects that are above Earth’s surface • The amount depends on the MASS of the object, Acceleration Due to Gravity and HEIGHT above the ground • GPE = mass X 9.8 m/s/s X height • GPE is measured in Joules also

  7. There are many forms of energy: • Electrical--movement of electrons • Radiant--from the sun) electromagnetic energy • Thermal –heat energy • Chemical—stored in bonds of atoms and molecules • Nuclear—stored in the nucleus of an atom

  8. Energy Conversions: • Transforming electrical energy • Happens all day, everyday • Ex: lightbulbs transform electrical energy into light • Some of the electrical energy is turned into thermal energy (hot bulbs) • Other ex: alarm clock, straighteners, toaster, etc.

  9. Transforming chemical energy: • Fuel is stored in the form of chemical potential energy • Engines transform chemical potential energy stored in gas into kinetic energy • Ex: a car engine—Fig. 7 in the textbook • Green plants convert light energy from the Sun into stored energy in chemical bonds

  10. Conversions between kinetic and potential energy • Many situations involve conversions between potential and kinetic energy • Ex: bicycles, roller coasters, swings, etc. • Mechanical energy is the total amount of potential and kinetic energy in a system • Mechanical energy = GPE + KE

  11. When energy is transformed from potential to kinetic, the potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same • Ex:—apple tree, baseball, swing

  12. Law of Conservation of Energy: • Kinetic and potential energy are constantly changing as the object speeds up and slows down • However, mechanical energy stays constant • So: -Energy cannot be created or destroyed, it simply changes form

  13. Friction and the Law of Conservation of Energy • Friction slows moving objects, which seems to decrease mechanical energy of an object. • However, friction converts energy to other forms such as thermal energy (heat)

  14. Converting Mass into Energy • Nuclear fusion—a special kind of energy conversion • During this process a small amount of mass is transformed into a tremendous amount of energy by fusing atomic nuclei (sun) • Nuclear fission—similar process, but nuclei are broken apart, not fused together

  15. Human Body –Energy Conversions • Complex chemical and physical processes in the body obey the law of conservation of energy • Energy is stored as fat and converted to energy as needed for life processes • 1 Calorie (C) is equal to 4,184 J • Every gram of fat supplies 9 C of energy • Section 2 Assessment questions

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