3. energy

Where is chemical energy stored

food, fuel, batteries

Where is kinetic energy stored

moving objects

Where is thermal energy stored

hot objects

Where is strain/elastic energy stored

stretched, squashed, twisted materials

Where is atomic/nuclear energy stored

atoms

Where is gravitational energy stored

objects in high places

System

something in which we are studying changes

Law of conservation of energy

energy can’t be created or destroyed

Units for energy

Joules (J)

Sankey diagram

shows the amount of energy transferred and where to

Energy transfer diagram

shows energy stores and transfers

Dissipated

spread out into the surroundings

How do mechanical processes become wasteful

when they cause a rise in temperature - energy dissipates through heating to the surroundings

Energy efficiency definition

how good a machine is at transferring energy into useful forms

given in a number between 0 and 1 or a percentage

Energy efficiency formula

useful energy transferred by device

total energy supplied to device

How can you reduce friction

lubrication - making a surface smooth so things can move easily on it

Insulation

slows the pace at which energy is transferred out of a place

Conduction

vibrations passed between particles in a solid

Convection

part of a fluid is warmer (less dense) and rises up, on the other side it is colder (more dense) and sinks down.

this creates a convection current going round in a circle

Radiation

energy transferred through waves, some types (infrared) can pass through solid objects

Thermal conductivity

how well a material allows heat to move through it

can depend on thickness and temperature difference

a good insulator needs low thermal conductivity

Solar energy

heating and lighting from the sun used with solar panels

Wind energy

using wind turbines, kinetic energy of wind turns a turbine

Hydroelectric energy

flowing water turns a turbine

Wave energy

kinetic energy of sea’s waves turned into electricity

Nuclear energy

energy in uranium nuclei is transferred into heating, creates steam and turns a turbine

Fossil fuels

chemical energy in coal, oil, gas transferred into heating, creates steam and turns a turbine

Biomass energy

chemical energy in things that were once alive burned and turned into heating

Geothermal energy

rocks underground are very hot, heat produces steam which turns a turbine

Tidal energy

water trapped behind a dam at high tide is released, turning a turbine