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.