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Chapter 15 Energy and Work Done - Notes

Chapter 15: Work and Energy

15.1 Energy and Work Done

  • Work is defined as the process of energy transfer that occurs when an object is moved over a distance by an external force.

  • SI Unit for Work and Energy: Joule (J)

What is Work?

  • Work is performed only when two conditions are met:

    • A force acts on an object.

    • The object moves in the same direction as the force.

Calculating Work Done

  • Formula:

    • Work (W) = Force (F) x Distance (d)

    • Units: Newton-meter = Joule (J)

  • Example calculations:

    • Maxi pushes a box with a force of 60N over 10m: W = 60N x 10m = 600J.

    • Peter bench presses 200N over 0.5m: W = 200N x 0.5m = 100J.

    • Kim lifts 150N, using 100J, calculate distance: d = 100J / 150N = 0.67m.

    • Fiona pushes a car uphill with 2.5kN (2500N) over 2.5m: W = 2500N x 2.5m = 6250J.

    • Jessie bench presses 1.5kN (1500N) using 3000J, calculate distance: d = 3000J / 1500N = 2m.

Conditions for Work

  • To do work on an object, both necessary conditions must be satisfied:

    • A force must act on the object.

    • The direction of movement must align with the direction of the force applied.

Example Questions

  • What is energy? It's defined as the ability to do work, measured in Joules (J).

  • What does 'work' refer to in physics? It involves the interaction of force and movement.

Vocabulary

  • Converted: Change in form or function.

  • Propels: To push or drive forward.

  • Conserved: Saved or protected from destruction.

Forms of Energy

  • Types of energy include:

    • M: Magnetic

    • K: Kinetic

    • H: Heat

    • L: Light

    • G: Gravitational potential

    • C: Chemical

    • S: Sound

    • E: Electrical

    • E: Elastic potential

    • N: Nuclear

  • Mnemonic: Great Name Mr. H.E.C.K.L.E.S.

Energy Changes

  • Work done indicates that energy is transferred from one form to another.

  • Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

Energy Transfer Diagrams

  • These diagrams illustrate how different types of energy are transferred or transformed through various processes.

  • Example: A car engine converts chemical energy from fuel into kinetic energy for movement.

Impact of Different Energy Sources

  • Non-renewable vs. Renewable energy sources:

    • Non-renewable: Fossil fuels (coal, oil, natural gas) are limited and result in pollution when used.

    • Renewable: Solar, wind, hydroelectric power sources are sustainable and less harmful to the environment.