Gravitational Potential Energy is energy stored because of an object’s position in a gravitational field. Kinetic Energy is energy stored in moving objects
where ΔGPE = Change in Gravitational Potential Energy (J), m = Mass (kg), g = Gravitational Field Strength (N/Kg) and Δh = Change in Height (m)
where KE = Kinetic Energy, m = Mass (kg) and v = Velocity (m/s)
Energy can be stored, transferred between stores and dissipated (meaning it is lost in less useful ways to the surroundings), but it can never be created or destroyed. The total energy of a closed system has no net change. Energy can be transferred mechanically, electrically, or by heating or radiation.
Diagrams can show how energy is transferred between stores. These stores can be in thermal, chemical, elastic potential, electrostatic, magnetic, nuclear, kinetic or gravitational potential stores.
| Example | Original Store | Transfer | Transferred Store |
| Object projected upwards | KE | Mechanical | GPE |
| Moving object hitting obstacle | KE | Mechanical, Sound | Thermal |
| Object accelerated by force | GPE | Mechanical | KE |
| Vehicle slowing down | KE | Mechanical through friction | Thermal |
| Boiling Water | Chemical | Electrical, Heating | Thermal |
Efficiency is only useful when it is transferred from one store to a useful store. Mechanical processes become wasteful when they cause a rise in temperature in the surroundings through dissipation. In all systems, energy is dissipated so that it is dissipated in different ways. This can be decreased by increasing the efficiency of a device, reducing friction in mechanical processes, or ensuring that all energy released burning fuel is used
Sankey Diagrams can be used to illustrate useful and wasteful energy transfers.
Energy can be transferred by conduction, vibrations passed on between particles in a solid, convection, currents in a liquid, or by radiation through gases, solids and vacuums.
Lubrication reduces frictional forces as objects move. For objects that are in contact, lubricant can be used to reduce friction between surfaces as they move. They are typically liquids like oil which can flow easily to coat these surfaces. Insulation slows down the rate at which energy is transferred by heating.
All objects have thermal conductivity, the ability of a material to transfer energy by conduction, but this conductivity can vary in levels. If decreased, less energy is transferred. Insulating materials can be used in the construction of houses, and walls can be made thicker. Cavity walls have an air gap between two walls, which reduces the energy transferred by conduction and keeping the house warm
| Biomass | Organic matter burnt for power or used to produce biofuels. Burning biomass requires little technology so is appropriate for LICs, but is only renewable if the resource is managed sustainably |
| Wind | Turbines use the energy of the wind to generate electricity, on- and off-shore, in wind farms. No greenhouse gas emissions but wind is variable |
| Solar | Energy from the sun generates electricity using photovoltaic cells. These are very expensive and only work during the day, but excess energy produced in homes can be sold to the grid |
| Hydro | Using energy of falling water. Water is trapped by a dam and allowed to fall through tunnels where it turns turbines to generate electricity. Building reservoirs destroys habitats and land |
| Tidal | Currents or tides are used to turn turbines and generate electricity. Although it does not work continuously, tidal cycles are regular so can be reliably predicted |
| Wave | Wind blowing across water makes waves which turn turbines and generate electricity. They are expensive and do not produce much energy in calm conditions |
| Geothermal | Water is pumped into the ground where heat in the crust turns it into steam which drives a turbine to generate electricity. Cheap to set up but only works in tectonically active areas |
| Fossil Fuel | Burnt to release energy. Emit CO2 and other greenhouse gases and contribute to climate change, and therefore usage is decreasing as more renewable resources are explored and used |
| Nuclear | Huge amounts of energy from very little fuel. However, plants are expensive to build and decommission, waste must be stored carefully for thousands of years and accidents can be deadly |