Energy, Work, and Power Summary

Energy, Work, and Power

Energy

  • Types of Energy:
  • Kinetic: Energy of motion, depends on mass and velocity: ( E_k = \frac{1}{2} mv^2 ). Examples: moving car, flying bird.
  • Gravitational Potential: Energy due to position in gravitational field: ( E_p = mgh ). Examples: water in a dam, book on a shelf.
  • Chemical: Energy in chemical bonds, released during reactions. Examples: burning wood, batteries.
  • Elastic (Strain): Energy stored when objects are deformed. Examples: stretched springs.
  • Nuclear: Energy within atom nuclei, released during fission/fusion. Example: nuclear plants.
  • Electrostatic: Energy due to electric charge interactions. Example: static cling.
  • Internal (Thermal): Total kinetic + potential energy of particles in a system. Example: hot cup of tea.

Energy Transfer

  • Energy transfers occur through:
  • Mechanical Work: Force moves an object.
  • Electrical Work: Battery transfers chemical energy to electric current.
  • Heating: Thermal energy transfer by conduction, convection, radiation.
  • Waves: Energy moved by electromagnetic and sound waves.

Conservation of Energy

  • Energy cannot be created or destroyed; only transformed. Total energy in a closed system remains constant. Example: energy transitions in a roller coaster.

Work

  • Definition: Work done when a force moves an object in the direction of the force.
  • Formula: ( W = Fd ) (Work done = Force x Distance moved).

Efficiency

  • Measure of useful energy output compared to total input.
  • Formula:
  • A. ( \text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \times 100\% )
  • B. ( \text{Efficiency} = \frac{\text{Useful Power Output}}{\text{Total Power Input}} \times 100\% )

Power

  • Definition: Rate of doing work or rate of energy transfer.
  • Formula:
    • A. ( P = \frac{W}{t} ) (Power = Work done / Time taken)
    • B. ( P = \frac{\Delta E}{t} ) (Power = Energy transferred / Time taken)
  • 1 Watt = 1 Joule/second.

Energy Resources

  • Renewable Sources: Solar, wind, hydroelectric, geothermal, biomass.
  • Non-Renewable Sources: Fossil Fuels, nuclear energy.

Advantages and Disadvantages of Energy Sources

  • Fossil Fuels: High energy, reliable but polluting.
  • Solar: Renewable but dependent on sunlight.
  • Wind: Clean but inconsistent availability.
  • Nuclear: High energy output but radioactive waste.

Efficiency Calculations

  • Example: Motor efficiency calculation: Producing 80% of useful output from input.
  • No system achieves 100% efficiency due to unavoidable losses (heat, friction).

Important Equations

  • Kinetic Energy: ( E_k = \frac{1}{2} mv^2 )
  • Change in Gravitational Potential Energy: ( \Delta E_p = mg\Delta h )
  • Efficiency example: Motor receiving 500J, output 400J: Efficiency = 80%.

Sample Questions Overview

  • Understand conservation of energy questions and calculations.
  • Be familiar with the efficiency and power calculations of systems.