1.4 Energy ⚡

Work (energy)

measure of energy transferred from one store to another

Work (forces)

force causes a displacement of the object

The equation linking work, force and distance (in the direction of the force)

work = force * distance

Unit for energy and work

Joules (J)

Unit for force

Newtons (N)

Unit for distance

Metres (m)

Equivalent of 1J

1J = 1Nm
e.g lifting a (1N) apple 1m

Alternative unit for work done by a force

Newton-metre (Nm)

Effect of doing work against friction

rise in the temperature of the object

Power

rate at which energy is transferred or work is done

The equation linking power, energy transferred and time

power = energy ÷ time

Unit for power

Watts (W)

Unit for time

Seconds (s)

One watt is equal to

1W = 1 J/s

The equation linking power, work done and time

power = work done ÷ time

how is work done affected by kinetic energy

to stop object, same amount of energy is required

Link between gravitational potential energy and kinetic energy

Gravitational potential energy at the top = kinetic energy at the bottom

Elastic potential energy

when an object is squashed it stores energy and is released when it returns

The equation linking kinetic energy, mass and speed

kinetic energy = 0.5 * mass * velocity squared

Unit for mass

Kilograms (kg)

Unit for speed or velocity

Metres per second (m/s)

The equation linking gravitational potential energy, mass, gravity and height

gavitational potential energy = mass * gravity * height

Unit for gravitational field strength

Newtons per kilogram (N/kg)

Unit for height

Metres (m)

Efficiency

how good device is at transferring total energy supplied (input) to useful energy stores (output)

The equation linking efficiency and energy

Efficiency = useful output energy transfer ÷ total input energy transfer

The equation linking efficiency and power

Efficiency = useful power output ÷ total power input

Why can't you have an efficiency greater than 1 or 100%

would break the law of conservation of energy as energy is being created

Reasons devices waste energy

• Friction between moving parts

• Heat due to electrical resistance

• Unwanted sound or light

Ways to improve efficiency

• Lubricate mechanical to reduce friction between moving parts

• Insulate heating to reduce dissipation of thermal energy

Energy resource

useful supply or store of energy

Non-renewable

sources used at a higher rate than can be replaced so will eventually run out (finite)

Examples of non-renewable resources

• Fossil fues (coal, crude oil, natural gas)

• nuclear fuels (uranium, plutonium)

Finite

has a limited number of uses before it runs out

Renewable

Energy sources that are replenished as they are being used so will not run out

Examples of renewable resources

Bio-fuels, solar, wind, geothermal, wave, tidal, hydroelectric

Advantages of wind energy

• renewable energy resource

• no fuel costs

• No harmful polluting gases are produced

disadvantages of wind energy

• noisy and may spoil the view for people living near them

• amount of electricity generated depends on the strength of the wind

• If there is no wind, there is no electricity

Advantages of wave, tide and falling water energy

• renewable energy resources and there are no fuel costs

• no harmful polluting gases are produced

• Tidal barrages and hydroelectric power stations are very reliable and easily switched on

Disadvantages of wave, tide and falling water energy

• difficult to make machines big enough to produce large amounts

• tidal barrages destroy places where birds and fish live

• hydroelectricity dams flood farmland and push people from their homes

• rotting vegetation underwater releases methane, which is a greenhouse gas

Advantages of geothermal energy

• a renewable energy resource and there are no fuel costs

• no harmful polluting gases are produced

Disadvantages of geothermal energy

• most places don’t have suitable areas where geothermal energy can be exploited

Advantages of solar energy

• renewable energy resource and there are no fuel costs

• no harmful polluting gases are produced

Disadvanages of solar energy

• only produce hot water in sunny climates, cooler areas need to be supplemented with a conventional boiler

• warm water can be produced on cloudy days but do not work at night

Advantages of nuclear power

• do not emit greenhouse gases such as carbon dioxide

• do not emit gasses such as sulphur dioxide

• 1 kg of nuclear fuel produces millions of times more energy than 1 kg of coal

Disadvantages of nuclear power

• fuels used for fission (uranium ore) are non-renewable since they wont last forever

• if there is an accident, large amounts of radioactive material could be released into the environment

• waste remains radioactive and hazardous for thousands of years, so must be stored safely

• decommissioning power plants is extremely expensive

Fossil fuels

Fuels formed from the remains of living organisms (coal, crude oil, natural gas)

Advantages of fossil fuels

• relatively cheap and easy to obtain- may not always be the case

• infrastructure is designed to run using fossil fuels

Disadvantages of fossil fuels

• non-renewable so supply is limited and will run out

• Coal and oil release sulphur dioxide gas when burned, causing breathing problems and acid rain

• release carbon dioxide when burned, adds to the greenhouse effect and increases global warming

Reliable (energy resource)

an energy resource that can supply enough energy to meet demand at predictable times

Examples of reliable resources

Fossil fuels, nuclear fuels, bio-fuels, tidal, hydroelectric and geothermal

Atmospheric pollution

• Carbon dioxide from burning fossil/ bio fuels

• sulfur dioxide from burning coal

Carbon neutral

Burning bio-fuels releases same amount of carbon dioxide as crops absorbed for photosynthesis

Closed system

a system (group of objects) with no net change to the total energy

Law of conservation of energy

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed

Useful energy transfer

energy is transferred to useful stores we want

Wasted energy transfer

energy transferred to useless stores we don't want, usually dissipates as heat

Dissipate

energy spreads out and is transferred to less useful energy stores, releasing heat

Insulate

reduce wasted energy by reducing amount of heat that transferred to surroundings

Thermal conductor

allows charge or heat to pass through it easily

• free electrons absorb heat, causing them to move faster

• they collide with metal atoms and transfer kinetic energy

• this causes the atoms to vibrate faster

Thermal insulator

does not allow charge or heat to pass through it easily

• have no free electrons so atoms absorb heat directly

• vibrations pass from atom to atom through the solid

• the process is much slower

Thermal conductivity

how well a material conducts energy when it is heated

Conduction

• transferred through solid

• vibrating particles collide and transfer energy to one another

• conductors have fast and free electrons which pass the energy very quickly

• slow process

Convection

• transferred through fluids (particles can move)

• particles with lots of heat energy move to take place of those with less heat energy

Radiation

• transferred from a hot object to cold

• no particles involved so can take place in vacuum

• object emitting infrared (heat) radiation

dull, matte, or rough dark surface

good absorber and emitter of heat but will cool quicker

shiny light surface

poor absorber and emitter of heat but will cool slower

how is heat loss caused in the home

mainly conduction and convection

examples of insulating materials

air, fibreglass, mineral wool

cavity wall insulation

gap between wall is filled with insulating material

loft insulation

thick layer insulating material reduces heat transfer through the ceiling by trapping air between fibres

double glazed windows

gap between two panes of glass contains air or gas insulator

Energy forms

• chemical

• heat

• electrical

• sound

• light

• magnetic

• strain/ elastic energy

• kinetic

• gravitational potential