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Chapter 4--Energy - PowerPoint PPT Presentation

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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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Chapter 4--Energy

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Chapter 4 energy

Chapter 4--Energy

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

Chapter 4 energy

  • 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

Chapter 4 energy

  • 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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