CO

Conservation of Energy

Conservation of Energy Notes

Energy Stores and Transfers

  • Definition: Energy is essential for initiating processes; it can move between various stores.
Energy Stores
  • Kinetic Energy: Stored in moving objects.
  • Thermal Energy: Stored in all objects, increases with temperature.
  • Chemical Energy: Stored in substances that can undergo chemical reactions (e.g., food, fuels).
  • Gravitational Potential Energy: Stored in objects within a gravitational field, dependent on height.
  • Elastic Potential Energy: Stored in stretched or compressed objects (e.g., springs).
  • Electrostatic Energy: Stored in charged objects interacting with each other.
  • Magnetic Energy: Stored in magnetic objects that interact.
  • Nuclear Energy: Stored in atomic nuclei, released in nuclear reactions.

Energy Transfers

  • Definition: Energy can be moved in and out of different stores or systems.
  • Closed System: An isolated system where no energy enters or leaves, ensuring net energy change is zero.
    • Example: A sealed thermos retains heat; energy cannot escape.
  • Methods of Energy Transfer:
    • Mechanically: Movement caused by forces (e.g., pushing, pulling).
    • Electrically: Movement of charge (current) through a voltage difference (e.g., circuits).
    • By Heating: Energy transfers from hot to cold objects (e.g., heating water).
    • By Radiation: Energy transfer through waves (e.g., sunlight).
Example of Energy Transfer
  • When boiling water in a kettle, energy is transferred from the heating element to the water, raising its thermal energy.

Work Done

  • Work done equals energy transferred; can be mechanical or electrical.
  • Examples of Work Done:
    • Throwing a ball transfers chemical energy from the muscles to kinetic energy of the ball.
    • Friction in slowing vehicles converts kinetic energy to thermal energy.

Conservation of Energy Principle

  • Energy can neither be created nor destroyed.
  • Changes in energy store during a process can be calculated using:
    • Kinetic Energy: KE = rac{1}{2}mv^2
    • Gravitational Potential Energy: GPE = mgh
  • Total energy input = useful energy output + wasted energy.

Dissipation and Efficiency

  • Not all energy transfers are useful; some energy dissipates, often as thermal energy to surroundings.
  • Efficiency: A measure of useful energy output versus total energy input.
    • Less wasted energy indicates greater efficiency.

Energy Transfer Diagrams

  • Diagrams visualize energy stores and transfers, using boxes for stores and arrows for transfers.
  • For example, throwing a ball upwards involves:
    • Loss of kinetic energy,
    • Gain of gravitational potential energy,
    • Heat loss due to air resistance.

Practice Questions

  • 1. Name eight energy stores.
  • 2. What is the net change in energy for a closed system?
  • 3. State the conservation of energy principle.
  • Application: Describe energy transfer in practical scenarios and illustrate with diagrams.