Law of Conservation of Energy: Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed.
Kinetic Energy: energy stored in a moving object
Equation: Ek = 0.5mv2
Ek: kinetic energy (J), m: mass (kg), v: speed (m/s)
Gravitational Potential Energy: energy stored in a falling object
Equation: Ep = mgh
Ep: graviational potential energy (J), g: gravitational field strength (9.8 m/s2), h: height (m)
Elastic Potential Energy: energy stored in a stretched or compressed object.
Equation: provided in exam
Efficiency: useful energy/ total energy or useful power/ total power.
Common energy transfers e.g. kettle: electrical, sound, kinetic, heat.
MAX GPE (at the top) = MAX KE (at the bottom).
When an object falls, some energy can be lost as heat or to the surroundings, but we assume no energy is lost.
Equation: provided in exam
P = E/t
P: Power (W), E: Energy transferred (J), t: time (s)
Work done is another word for energy transferred.
Unwanted energy transfers can be reduced by using lubrication or thermal insulation.
The higher the thermalconductivity of a material the higher the rate of energy transfer by conduction across the material.
Heat transfer in solid: conduction; a particle gains heat and vibrates more, so it bumps into nearby particles and transfers heat.
Thicker walls, lower conductivity help to keep heat inside the house.
Main energy resources: fossil fuels (coal, oil, gas), nuclear, bio-fuel, wind, hydroelectricity, geothermal, tidal, solar, water waves.
A renewable energy resource is one that is being (or can be) replenished as it is used. The uses of energy resources include: transport, electricity generation and heating.