energy

Energy

  • Definition: Energy is never created or destroyed; it is only transferred.

  • Energy Transfer: When a system changes, energy is transferred from one form to another.

    • Example: Electrical energy changes into kinetic energy in a motor.

Closed System

  • Definition: A closed system is a system that experiences no external forces.

  • Examples:

    • A circuit

    • A skydiver

  • Characteristic: In a closed system, the total energy remains constant at all times.

Changes in Energy

Gravitational Potential Energy

  • Formula: \Delta GPE = mg\Delta h

    • Change in gravitational potential energy (joule, J) is calculated as:

    • Mass (kilograms, kg) × Gravitational field strength (newton per kilogram, N/kg) × Change in vertical height (metres, m)

Kinetic Energy

  • Formula: KE = \frac{1}{2} mv^2

    • Kinetic energy (joule, J) is calculated as:

    • \frac{1}{2} × Mass (kilograms, kg) × Speed squared ((metre/second)², (m/s)²)

Work Done

  • Definition: Work done refers to the transfer of energy to a system by an external force.

  • Example: A human doing work to push a ball up a hill.

Energy Transfer Forms

Electric

  • Chemical Potential Energy: This energy, stored in batteries, is converted into electric energy.

Heating

  • Energy Transfer: Electric energy transfers into thermal energy when work is done against heating coils, causing them to heat up.

Work Done Formula

  • Formula: E = Fd

    • Work done (joule, J) is calculated as:

    • Force (newton, N) × Distance moved in the direction of the force (metre, m)

Waste Energy

  • Energy Transfer Efficiency: Energy is rarely 100% transferred into the desired form, leading to waste.

  • Dissipation: Some energy is dissipated and stored in less useful ways.

  • Mechanical Processes:

    • Wasteful when they generate heat (often due to friction).

    • Energy is lost to the surroundings as heat, causing an increase in temperature.

Power

  • Definition: Power is the rate at which energy is transferred.

  • Formula: P = \frac{E}{t}

    • Power (watt, W) is calculated as:

    • Energy transferred or work done (joule, J) ÷ Time taken (second, s)

    • 1 Watt = 1 Joule/second

Efficiency

  • Definition: Efficiency measures how much energy is not lost as waste.

  • Formula: \text{Efficiency} = \frac{\text{Useful Output Energy}}{\text{Total Input Energy}}