Energy

Gravitational potential energy equation

ΔGPE(J) = m × g × Δh

m= mass(kg)

g= grav field strength(N/kg)

h= height(m)

kinetic energy equation

KE = ½ mv²

m= mass(kg)

v=speed(m/s)

system

An object or group of objects

closed system

A system where there is no net change to the total energy in that system

Why must the total amount of energy in a closed system stay the same?

Because of the conservation of energy

Principle of energy conservation

Energy cannot be created or destroyed, it can only be transferred from one store to another

Is energy ‘lost‘ in a system?

No, it is dissipated(spread out to the surroundings)

energy store - kinetic

a moving object has a kinetic store of energy

energy store - gravitational 

When objects are lifted above ground they gain energy in their gravitational potential store

energy store - elastic

Objects have energy in their elastic potential store if they are stretched

energy store - electrostatic

When objects with charge interact with one another they gain energy in their electrostatic store

energy store - magnetic

When magnetic objects ineract with one another, they gain energy in their magnetic store

energy store - chemical

Objects with energy in their chemical store can release energy in chemical reactions

energy store - nuclear

Atomic nuclei release energy from their nuclear store during nuclear reactions

energy store - thermal

all objects have energy in their thermal store

the hotter the object the more energy it has in its thermal store

4 energy transfer types

• Mechanically

• Electrically

• By heating

• By radiation

energy transfer - mechanical

when a force acts on an object

i.e. stretching, pulling, pushing

energy transfer - electrical

A charge moving through a potential difference

i.e. charge flowing through an object

energy transfer - heating by particles

energy transfers from a hotter object to a cooler one

energy transfer - heating by radiation

energy transferred by EM waves

i.e. light

How to draw sankey diagrams

Straight arrow represents useful energy

Arrow(s) that bend down represent wasted energy

WIdth of useful energy arrow + wasted energy arrow(s) = width of total energy input

Quantity of energy useful/wasted corresponds with the width of those arrows

energy transfers of a ball being thrown upwards

Person’s chemical energy - KE of ball - GPE of ball

energy transfers of a car hitting an obstacle

chemical store of fuel - KE of car - thermal energy of surroundings + obstacle(mechanically)

energy transfers of a car slowing down

KE of car - thermal energy of surroundings via friction between tyres and ground and between brakes and brake pads

energy transfers of a boiling water in a kettle

Energy transferred electrically from mains supply to the thermal store of water

Also, thermal energy transferred by heating to the thermal store of water

energy transfers of jumping in a trampoline

elastic potential - KE - GPE

useful energy

An energy transfer that serves an intended purpose

wasted energy

An energy transfer that is not useful for the intended purpose and is dissipated to the surroundings

wasted and useful energy of bat hitting ball

useful - KE of ball

wasted - thermal store of surroundings, bat and ball

Explain how can energy dissipation be useful?(2)

Television - useful energy is energy by radiation of visible light and by heating as sound waves; wasted energy is thermal energy dissipation

Heater - useful energy is energy transferred from mains supply to heating element and then dissipated to the surroundings by heating; wasted energy is the dissipation of energy via radiation as visible light

How to reduce energy loss(2)?

Lubrication

insulation

How does lubrication reduce energy loss

Reduces the amount of friction between working parts

therefore, less energy is wasted to thermal store of working parts and person has to do less work to make the bike move

How does insulation reduce energy loss

Reduces energy transfer via conduction by reducing the passing of vibration of particles which is how energy is conducted

3 factors of effectiveness of insulator and why?

• The thermal conductivity of the material

  • The lower the conductivity, the less energy is transferred 

• The density of the material

  • The more dense the insulator, the more conduction can occur

  • In a denser material, the particles are closer together so they can transfer energy to one another more easily

• The thickness of the material

  • The thicker the material, the better it will insulate

What is house insulation often made from and why?

Glass fibre as there is air trapped between woven fibres which reduces density

Glass can’t conduct heat that well as well, thus it is suitable for insulation

thermal conduction

the process where energy is transferred by vibrating particles in a substance

The vibrating particles transfer energy from their kinetic store to the kinetic store of neighbouring particles

Direction of energy transfer in conduction

hot to cold

The higher the thermal conductivity of a material………

the higher the rate of energy transfer by conduction across the material

How long does it take relatively to heat something up with good vs poor thermal conductivity

Good is quicker to heat up

Poor takes longer to heat up

Example of good thermal conductor

metal

Examples of bad thermal conductor

Non-metals are poor thermal conductors whilst liquids and gases are extremely poor

When will objects stop cooling down

until they reach thermal equilibrium (equal temperature) with their surroundings

example of thermal equilibrium

a coffee mug cools down until it reaches r.t.p

Factors affecting thermal conduction

• The thickness of the material

• The thermal conductivity of the material

• The temperature difference between two areas of the material (for example the internal and external surfaces of a wall)

How can the rate of energy transfer by conduction be reduced?

• Increasing the thickness of the material

• Decreasing the thermal conductivity of the material

• Decreasing the temperature difference

efficiency

The ratio of the useful energy output from a system to its total energy output

efficiency equation

useful energy output/ total energy input

How can efficiency be reduced?(4)

• Reducing Friction between their moving parts

• Reducing Air resistance

• Reducing Electrical resistance

• Reducing Noise

How can electrical resistance be reduced to improve efficiency?(2)

• Using components with lower resistance

• Reducing the current 

How can noise be reduced to improve efficiency?(2)

• Tightening loose parts to reduce vibration

• Lubricating parts

How can air resistance be reduced to improve efficiency?

Streamlining the shape of moving objects

Renewable energy resources(6)

• Solar energy

• Wind

• Bio-fuel

• Hydroelectricity

• Geothermal

• Tidal

Non-renewable energy resources(2)

• Fossil Fuels (coal, oil and natural gas)

• Nuclear fuel

How is energy generated regardless of energy resource?

• A turbine is turned, which turns a generator, which generates electricity

• The element that differs is how the turbine is made to turn

fossil fuels

combusted to heat water to produce steam to turn turbine and generate electricity

advantages of fossil fuels

reliable

can produce large amounts of energy in fairly short notice

disadvantages of fossil fuels

significant ghg emission and pollution

non renewable

nuclear

nuclear fuels are reacted to produce water - steam - turbines - electricity

advantages of nuclear

reliable

no ghg emission

large amount of energy produced from small amount of fuel

disadvantages of nuclear

produce dangerous radioactive waste that can take thousands of years to decay

non-renewable

biofuels

plant matter/ethanokl/methane

can be used in place of fossil fuels

advantages of biofuels

renewable

net CO2 emission is 0 as CO2 released when burning fuel = CO2 absorbed whilst producing fuel

disadvantages of biofuels

can take up a lot of land and consume resources that are needed for food production

wind

turn turbines directly to produce electricity

advantages of wind

renewable

no ghg emission or pollution

land still usable for farming

disadvantages of wind

unreliable due to dependence on if its a windy day

can be visually unappealing and noisy

not everywhere is suitable

hydroelectric

water stored at a height and when released rushing water turns turbines directly to generate electricity

advantages of hydroelectric

renewable

no ghg emission

can produce large amount of energy in short notice

disadvantages of hydroelectric 

can involve flooding large area

can destroy important wildlife habitats

tidal

Movement of water due to tides turn turbines directly to produce electricity

advantages of tidal

renewable

tides very predictable

large amounts of energy can be produced at regular intervals

disadvantages of tidal

very few suitable locations

can cause environmental harm and affect shipping

geothermal

hot rocks underground heat water - steam - turbines - electricity

advantages of geothermal

renewable

reliable

geothermal stations are usually small

disadvantages of geothermal

can result in release of harmful gases from underground

not many places are suitable

solar

Use light to generate electricity

solar panels use thermal radiation to heat water - steam - turbines - electricity

advantages of solar

renewable

no ghg emission or pollution

good for producing energy in remote places

disadvantages of solar

unreliable as only works when sunny

solar farms can use up lots of sunland

3 main uses of energy resources and which energy resource they use

• Transport - mainly fossil fuels(crude oil), though now more cars are being powered by electricity

• Electricity generation - mainly fossil fuels

• Heating - natural gas(fossil fuel) or in geologically active countries such as Iceland, geothermal energy is used for heating