Energy Stores and Transfers

  • Energy Stores: Energy can be stored in various forms within matter.
    • Kinetic Energy: Energy of motion (particles, objects).
    • Gravitational Potential Energy: Energy due to position in a gravitational field.
    • Chemical Energy: Stored in molecular bonds.
    • Elastic Energy: Stored in stretched springs or compressed objects.
    • Nuclear Energy: Stored in the nucleus of atoms.
    • Electrostatic Energy: Stored in electric fields.
    • Internal (Thermal) Energy: Random motion of particles.
  • Energy Transfers: Energy moves between objects or stores.
    • Mechanical Work: Force moving an object.
    • Electrical Work: Moving electricity through a circuit.
    • Heating: Transfer via thermal energy.
    • Waves: Transfer via sound or light.
  • Conservation of Energy: Energy cannot be created or destroyed. It only changes from one store to another. Total energy remains constant. Image description: Sankey diagram showing energy flow through a power cycle

Work

Work represents energy transferred or stored from one place to another. $$ \text{Work} = \text{Force} \times \text{Displacement} $$ $$ \text{W} = \text{Fd}$$

Work is done only when force moves an object in the direction of the force.

Energy Equation: $$\text{W} = \Delta \text{E}$$ (Work done equals the change in energy).

  • Example: Pushing a refrigerator requires mechanical work. The energy transfers from the chemical energy in the body (respiration) to kinetic potential energy in the refrigerator. Image description: Diagram illustrating mechanical work pushing an object

Energy Resources

  1. Fossil Fuels: Coal, oil, natural gas. High energy density, limited supply, released over millions of years.

  2. Biofuels: Plant and animal material. Renewable, lower energy density, requires land/space.

  3. Water: Tidal, wave, and hydroelectric. Renewable, reliable, high capacity.

    • Example: Dam creates head pressure to turn turbines.

  4. Geothermal: Heat from Earth’s interior. Reliable, low environmental impact, limited geographic availability.

  5. Nuclear: Uranium or plutonium fission. High energy, long-lived fuel.

    • Example: Nuclear reactor produces massive heat for electricity generation.

  6. Solar: Photovoltaic cells and solar thermal. Renewable, abundant, intermittent.

    • Example: Solar panels on buildings convert sunlight to electricity.

  7. Wind: Turbines capturing kinetic energy of air. Renewable, variable.

Roles of Boiler, Turbine, Generator:

Boiler: Converts fuel to steam.
Turbine: Converts thermal energy to rotational motion.
Generator: Converts mechanical motion to electrical energy.

Energy Resources Table

Resource Renewability Availability Reliability Scale Environment
Coal/Oil No Finite High Large High impact
Biofuels Yes Limited Medium Small/Medium Low impact
Tidal Yes Low High Small/Medium Low impact
Geothermal Yes Local High Medium Low impact
Nuclear No Finite High Very Large Waste/Heat
Solar Yes High Low Large Low impact
Wind Yes Medium Low Medium/Small Low impact
  • Concept of Efficiency: No system converts 100% of energy. Some energy is lost as heat.
  • Efficiency = (Useful Energy Output / Total Energy Input) $\times$ 100%
  • Comparison: Efficiency allows us to compare how well different resources or machines perform.

Efficiency and Power

  • Power: Rate of energy transfer or storage. Power is energy per unit time.
    • Formula: $P = \frac{\Delta E}{t}$
    • Unit: Watt (W).
  • Efficiency Formula (Power): $\text{Efficiency} = \frac{\text{Useful Power Output}}{\text{Total Power Input}} \times 100%$
  • Examples:
    • Nuclear Energy: Fusion in the Sun is the primary energy source for the Sun. Fusion research aims for large-scale electrical energy production on Earth.
    • Solar Energy: Photovoltaic cells convert sunlight to electricity with varying efficiency depending on panel quality.
    • Wind Energy: Turbines convert wind speed to electricity. Efficiency depends on wind strength.