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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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the nature of 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
slide3
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
kinetic energy
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)
potential energy
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)
gravitational potential energy gpe
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
there are many forms of energy
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
energy conversions
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.
transforming chemical energy
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
conversions between kinetic and potential energy
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
slide11
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
law of conservation of energy
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
friction and the law of conservation of energy
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)
converting mass into energy
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
human body energy conversions
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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