Energy Stores and Transfers

Key Concepts in Energy and Its Conservation

Definitions

  • Conservation: The principle that the total value of a quantity remains constant before and after a change.
  • Efficiency: The percentage of energy that is utilized for a useful task, contrasted with the amount that is wasted.
  • Energy Store: Refers to a form of energy that can be stored in different states or forms.
  • Energy: A mechanism capable of transferring from one store to another form.
  • Gravitational Potential Energy (GPE): The energy stored in an object due to its height above the ground. When an object falls, this energy converts into kinetic energy and heat.

Units of Energy

  • Joule (J): The unit measurement for energy, denoted by the symbol [J].
  • Kinetic Energy (KE): Also referred to as movement energy; the energy an object possesses due to its motion.
  • Mass: The quantity of matter in an object, measured in kilograms (kg).

Energy Transfers

  • Sankey Diagram: A visual representation of energy conservation that illustrates how much energy is useful and how much is wasted.

Different Forms of Energy Storage

  • Kinetic Energy Store:

    • Description: Energy stored in moving objects (e.g., a running person, a car on the road).
    • Examples: A speeding car, a thrown ball.

  • Gravitational Potential Energy Store:

    • Description: Energy stored in an object when raised above the ground (e.g., a book on a shelf).
    • Examples: Water in a dam, objects at height.

  • Chemical Energy Store:

    • Description: Energy stored in chemical bonds; these bonds can release or absorb energy during reactions.
    • Examples: Fuels, batteries, and foods.

  • Elastic Potential Energy Store:

    • Description: Energy stored in materials that can be stretched or compressed (e.g., slingshots, catapults).
    • Examples: A stretched spring or a drawn bow.

  • Magnetic Energy Store:

    • Description: Energy associated with magnets and magnetic fields.
    • Examples: Fridge magnets, magnetic motors.

  • Electrostatic Potential Energy Store:

    • Description: Energy stored between charged objects, such as in electric fields.
    • Examples: Lightning strikes, charged balloons.

  • Nuclear Energy Store:

    • Description: Energy stored in the nucleus of atoms, released during nuclear reactions.
    • Examples: Nuclear power plants, atomic bombs.

  • Thermal Energy Store:

    • Description: Energy stored in an object due to its temperature, associated with the motion of particles.
    • Examples: Heat energy in a cup of tea or a hot bath.

Energy Transfers Mechanisms

  1. Mechanically: Energy is transferred when a force is applied over a distance.

    • Example: Pushing a box across the floor.

  2. Electrically: Transfer of energy occurs when electric charges move through a circuit.

    • Example: Energy transferred to a light bulb.

  3. By Heating: The transfer of energy from a hotter object to a cooler one.

    • Example: Heating the surroundings around a hot object.

  4. By Radiation: Energy is transferred through light waves or electromagnetic waves.

    • Example: Heat from the sun reaching the Earth.

Principles of Efficiency

  • Efficiency: Refers to how effectively a system utilizes energy, defined as:
    • \text{Efficiency} = \frac{\text{useful energy output}}{\text{total energy input}}
    • Percentage Efficiency: \text{% efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%
    • Example: For a light bulb with 40% efficiency:
    • Useful energy output: 40J
    • Total energy input: 100J
    • Efficiency calculation: \frac{40}{100} = 0.4 = 40\%

Energy Changes in Systems

  • Energy changes can be analyzed through the identification of starting and ending energy states, and the mechanisms involved in energy transfer.

  • Example: A person lifting a dumbbell

    • Start: Chemical Energy
    • End: Gravitational Potential Energy
    • Transfer Mechanism: Mechanically
    • Change: Increases in GPE and decreases in chemical energy.

  • Further Examples with Analysis:

    1. A skydiver falling from an airplane
    • Start: Gravitational Potential Energy
    • End: Kinetic Energy
    • Transfer Mechanism: Mechanically
    1. Burning a piece of coal
    • Start: Chemical Energy
    • End: Thermal Energy
    • Transfer Mechanism: By heating.

The above notes encapsulate the wide-ranging definitions and applications of energy storage and transfers, demonstrating the core scientific principles and examples relevant to the subject.