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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


  • 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



Law of conservation of energy
Law of Conservation of Energy: potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same

  • 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 potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same

  • 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 potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same

  • 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 potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same

  • 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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