1.4 Energy

Work (in terms of energy)

A measure of the energy transferred from one store to another

Work (in terms of forces)

When the force causes a displacement of the object

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

work = f * d

Unit for energy and work

Joules (J)

Unit for force

Newtons (N)

Unit for distance

Metres (m)

What one joule is equal to

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, the 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 a device is at transferring energy input to useful energy output

Total input energy

The total amount of energy supplied to a device

Useful energy output

The amount of energy that is transferred to useful energy stores

Wasted energy output

The amount of energy that is wasted or dissipated to the surroundings e.g heat

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

Percentage efficiency

multiplying the efficiency by 100

What is meant by an efficiency greater than 1 or 100%

More energy is being transferred than is being supplied

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

1. Friction between moving parts

2. Heat due to electrical resistance

3. Unwanted sound or light

Ways to improve efficiency

1. Lubricate mechanical to reduce friction between moving parts

2. Insulate heating to reduce dissipation of thermal energy

Energy resource

A 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 fuels (coal, crude oil, natural gas)

nuclear fuels (uranium, plutonium)

Finite

Something that 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

Replenishing renewable resources

Human action, natural processes

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

Nuclear fuels

radioactive materials e.g uranium ore

Bio-fuels

plant and animal waste e.g wood

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

Environmental impact

damage to the environment caused by using an energy resource

Pollution

damage to the land, air or water caused by a toxic chemical or object

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

system 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 is transferred to useless stores we don't want

Dissipate

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

Lubricate

reduce wasted energy by reducing friction between moving parts

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

rate of energy transfer by conduction through a material

Conduction

transferred through solid

vibrating particles collide and transfer energy to one another

comductors have fast and free electrons which pass the energy very quickly

slow process

Convection

transferred through fluids

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

fluid

liquids and gasses, made to flow as the particles can move from place to place

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 insulators

air, fibreglass, mineral wool

cavity wall

gap between two brick walls contains air, an insulator

cavity wall insulation

gap 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

System

An object or group of objects

Kinetic energy

The energy of a moving object

Heat (thermal) energy

energy of the particles in an object due to its temperature

Light (radiant) energy

carried by a light wave

Gravitational potential energy

when an object is raised against gravity

Chemical energy

stored in food, fuels and batteries

Sound energy

released by vibrating objects

Elastic potential energy

stored when an object is stretched or squashed

Electrical energy

stored from moving charges or static electric charges

Nuclear energy

stored in the nuclei of atoms

Magnetic energy

when repelling poles are pushed together or attracting pulled apart

Doing work

scientific way of saying that energy has been transferred

Energy

The capacity to do work