Physics GCSE 4.1 Energy

Energy stores

Kinetic - energy of motion

Gravitational potential - energy due to height

Elastic potential - Energy in stretched/compressed objects

Chemical - stored in bonds (muscles in humans)

Thermal - temperature

Electrostatic, magnetic, nuclear

System (open and closed)

Portion of the physical universe that you’ve chosen to analyse

Matter can exchange energy with environment (outside) (can lose or gain energy)

No energy can be gained or lost in a closed system - Overall energy change is always 0

Boiling water in Kettle energy transfer

Electrical energy from the Plug socket flows to heating element of kettle

It is transferred electrically to the thermal energy store of the kettle’s heating element

The thermal energy is then transferred to the water’s thermal energy store, heating it up

Mechanical work done

Involves using a force to move an object

e.g: Kicking the ball in the air - chemical energy from foot transferred to balls kinetic energy store

Electrical work done

Done when current flows

Energy required to overcome the resistance in the wires of a circuit

Object slowing down energy transfer/work done

To stop, object (car, train etc.) applies brakes creating friction between the brakes and the wheels

The friction “does work” as it slows the train down

Causes the energy in the wheels kinetic energy stores to be transferred to the thermal energy stores of the surroundings in the form of heat

A coal fire energy transfer example

Coal has a large store of chemical energy (energy within chemical bonds).

When coal is burned the chemical energy is transferred by heating to the thermal energy store of the coal.

Hot coals and flames transfer energy to the surroundings by heating and radiation.

Car braking energy transfer example

The moving car has kinetic energy.

The brakes mechanically do work on the car to slow it down.

The kinetic energy of the car decreases and the thermal energy store of the brakes increases.

Archery firing a bow and arrow energy transfer example

As the string of the bow is pulled back chemical energy in the archers muscles is transferred mechanically to the elastic potential of the bow.

When the archer releases the string of the bow, the elastic potential energy of the string is transferred mechanically to the kinetic energy store of the arrow.

Kinetic Energy

The kinetic energy of an object is the energy that it possesses due to its motion.

Amount depends on object’s speed and mass

The faster the object is moving, the more KE it has

The more mass an object has the more KE it has

Kinetic Energy Equation

KE = ½ mv²

Kinetic energy (J) = ½ Mass (kg) x Velocity²(m/s)

Gravity

Force of attraction between 2 objects

Size of force depends on Mass of objects and How far apart the objects are

Gravitational Field

Field of gravity’s influence around an object

Strength of this field is Gravitational field strength

On earth gravitational field strength is (9.8 N/kg)

Weight

Force exerted on an Object due to Gravity

Depends of mass object and gravitational pull

Weight (N) = mass (kg) x gravitational field strength

Weight changes based on what planet your on (gravitational field strength changes) whereas mass never changes

Gravitational Potential Energy

Energy required to lift an object up and overcome force of gravity

Formula: GPE = mgh

Gravitational potential energy (J) = mass (kg) x Gravitational field strength (N/kg) x Height (m)

Elastic potential energy

Amount of elastic potential energy stored in a stretched spring calculated using:

EPE = ½ k e²

Elastic potential energy = 0.5 x Spring constant x (extension) ²

Assuming the limit of proportionality has not been exceeded

Transfer between Kinetic Energy and Gravitational Potential energy

As an object rises, KE is converted to GPE

As an object falls, GPE is converted to KE 

KE lost = GPE gained

KE gained = GPE lost

Internal Energy

Total energy stored by the particles making up a substance or system

Potential energy stores and Kinetic energy stores

Temperature

Temperature is a measure of the average internal energy of a substance

When a substance is heated up, thermal energy is transferred to the kinetic energy stores of the particles of the substance, increasing their internal energy - measured as an increase in temperature

Specific Heat Capacity

Amount of energy needed to raise the temperature of 1kg of a substance by 1 Degree Celsius

Also - amount of energy released as a substance cools

Specific Heat Capacity Equation

ΔE = mcΔθ

Change in Internal Energy (J) = mass (kg) x Specific Heat Capacity (J/kg°C) x Change in temperature (°C)

c of water = 4200 J/kg°C

Conservation of Energy Principle

Energy can be transferred usefully, stored or dissipated (as wasted energy like heat), but can never be created or destroyed

Can only move between different objects

How heat energy is transferred

Conduction

Convection

Radiation

Conduction

Heat energy is transferred through collisions between neighbouring vibrating particles

When solid is heated up, particles gain more KE therefore vibrate more and collide with neighbours more often - transferring heat energy throughout object

Happens mainly in solids as particles are packed closely together making it easier for them collide

Thermal conductivity

Describes how well a material conducts heat

Metals have high thermal conductivity

Non-metals and fluids have low thermal conductivity (insulator - material doesn’t conduct heat well)

Convection

Heat energy is transferred by particles moving position, rather than just vibrating

Happens most in fluids

When fluid particles are heated, they gain KE and start to move faster.

As they move faster, they spread apart, making the heated fluid less dense

The less dense heated fluid rises above cooler, denser fluid which then heats up as it is nearer to heat source and the less dense fluid cools down and sinks back down again, creating a convection current

Radiation

When heat energy is transferred without particles - uses infrared waves - can even travel through a vacuum (like space) where there are no particles at all

Hotter objects emit more radiation

Cooler objects emit less radiation

Reducing unwanted energy transfers

Thermal insulation

Lubrication

How do we prevent heat from escaping homes (Convection)

House is sealed closed

Foam seals on windows and curtains drawn at night-

Prevents heat loss from convection

How do we prevent heat from escaping homes (Conduction) - walls

Conduction can be prevented from walls

• Thick walls (made from materials with low thermal conductivity)

• Tend to have cavity walls (2 layers of bricks with air gap in between reducing conduction - air is a bad conductor)

• Air gap still allows convection therefore is filled with insulating foam (lots of isolated air bubbles - reduces convection and conduction)

How do we prevent heat from escaping homes (Conduction) - windows

• Single glazing windows - one pane of glass - heat is easily lost

• Double glazing windows - two layers of glass with a tiny air gap in between - reduces conduction of heat

Reducing Friction

Friction - Resistance an object encounters when moving a solid/through fluid

Reduces efficiency of energy transfer as object heats up

Can be reduced by adding a lubricant by oil to reduce friction

Can be reduced by making objects (cars, planes etc.) streamlined therefore we reduce friction from air resistance - using less fuel / more efficient

Power 1

Power is the rate at which energy is transferred

P = E/T

Power (N) = Energy Transferred (J)/Time taken to transfer energy (s)

Power 2

Power is the rate at which work is done

P = W/T

Power = Work done/Time

Work done definition

Measure of energy transferred. When a force is used to move an object by a certain distance

Efficiency

Proportion of the energy supplied transferred into useful energy output

Efficiency = Useful energy/power output / Total energy/power input

Efficiency (lamp example)

Input - electrical energy

Output - Light energy and Heat energy

Light energy is useful energy output whereas heat energy is wasted energy output (not purpose of the lamp)

Non-renewable energy sources

Fossil fuels - coal, oil and gas

Renewable energy sources

Resource that is being or can be replenished as it is used

Solar, Wind, Hydroelectric, Geothermal, Biofuels and Tidal

Energy used for transport in UK

Transport: petrol/diesel for cars + Kerosene for flight. Electricity for trains (used to be coal)

Increased use of biofuels (renewable) and electric cars

Energy used for Domestic reasons in UK

Domestic: Cooking + Heating - natural gas burnt to heat water which is then pumped into radiators - thermal energy transferred to air inside rooms

Coal can also be used in fire places

Renewable sources of energy for heat: Solar water heaters and biofuels

Electricity generation

Isn’t renewable or non-renewable - depends on how it is made

Main sources of electricity in UK are from non-renewable sources

Fossil Fuels

A fossil fuel is a hydrocarbon-containing material formed naturally in the earth's crust from the remains of dead plants and animals.

Three main types: Coal (solid), Crude oil (Liquid), Natural gas (gaseous)

Uses of Fossil Fuels

Fossil fuels may be burned to provide heat.

Heat can be used to:

Burned to provide heat for direct use (e.g. cooking)

To power engines (e.g. the internal combustion engines in cars)

To generate electricity

Pros of Fossil Fuels

Relatively cheap

Can be used in any conditions (e.g. don't require wind or sunshine to work)

Much of our current infrastructure is designed to run using fossil fuels (e.g. most of our cars use petrol or diesel which are both made from crude oil)

Cons of Fossil Fuels

They're a limited resource so will run out one day

They produce carbon dioxide when burned, which is a greenhouse gas and contributes to global warming

They sometimes produce toxic gases when burned - such as sulfur dioxide and carbon monoxide

Nuclear energy

Nuclear energy is energy obtained via nuclear reactions, such as nuclear fission reactions in nuclear power stations.

This energy can be used to generate electricity, which can then be transmitted to homes and factories across the country. 

Pros of Nuclear Energy

Nuclear fuels do not produce any pollutants like sulphur dioxide, or greenhouse gases like carbon dioxide
Can be used in any conditions (e.g. nuclear power doesn't depend on environmental forces like sunshine or wind)
Although nuclear fuel (like uranium) is a limited resource, it is very unlikely to run out for a very long time 

Cons of Nuclear Energy

Nuclear fuels (like uranium) are technically a finite resource (although nuclear power stations only use very tiny amounts so it won't run out any time soon)

Nuclear power stations produce radioactive waste, which remains harmful for thousands of years and so must be stored very carefully

It is quite expensive 

If there is a problem at the power station, there is a very small chance of a nuclear meltdown which could release large amounts of radioactive material into the environment

Wind Power

Captured through the use of Wind Turbines

Placed in exposed areas where there are strong winds

Each turbine have generators inside them - when the blades spin from the wind - the generator turns - kinetic energy from movement is turned into electrical energy

Solar power

Generated from solar cells (panels) - generate electric currents directly from sunlight

Work in low energy devices like watches and calculators and Remote regions that aren’t connected to main power grid

Can be used in larger towns

Pros of wind and solar power

Low running costs

Don’t produce pollutants - no Co2

Don’t damage the environment

Getting cheaper every year

Cons of Wind and Solar Power

High upfront costs

Process of making them produces pollutants

Dependent on weather

No way to increases supply in times of peak demand

Take up lots of space

“Don’t look nice” + Too Noisy

Geothermal energy

Geothermal Energy: Energy stored in the Earth’s crust - heat energy originated from initial formation of the planet + from ongoing radioactive decay from materials like uranium deep inside the earth

Can be used directly for heat or to generate electricity

Geothermal power to produce heat and electricity

Heat:

Pump water into the ground

Water warms up from geothermal energy

Water then pumped back onto surface

Electricity:

Leave water underground for so long it turns to steam

Gas rises and turns turbines which drive generators to produce electricity

Pros and Cons of Geothermal Power

Pros:

Installing only damages environment slightly

Doesn’t produce any pollutants

Renewable

Reliable over long periods

Cons:

Can only be used in certain areas (volcanic regions)

Power plants required can be expensive to build

Biofuels

Fuels made from recently living organisms

plants or algae - lock up sun’s energy

Carbon neutral - release co2 but took up co2 when growing

Pros and Cons of Biofuels

Pros:

Renewable resource

Relatively cheap to make

Easy to transport

Can mix with fossil fuels

Cons:

Need somewhere to grow (means converting natural land - cutting down forests releasing Co2)

Harvesting processing and Transport require energy - more co2 released

Hydroelectric Dams and Tidal Barrages Function

Big dam prevents water from flowing causing a higher water level on one side

Hydroelectric dams: traps the water from upstream which accumulates large amount of water (reservoir)

Tidal Barrages: Use tides which rise and fall on sea level due to moon’s gravity - occurs in estuaries (where river meet the ocean)

Traps water as tide comes in - higher water level on one side

Generating electricity from Hydroelectricity and Tidal barrages

Stored water has huge gravitational potential energy - differences in water level generates electricity

Water that is released from reservoirs behind the dams spin the blades of the turbines inside the dams which are connected to generators that generate electricity as they spin which causes water to then flow back into the river on the other side of the dam

Pros of Hydroelectric dams and Tidal barrages

Large amounts of energy with no pollution

Reliable sources of electricity

Low running costs

Work on large and small scales

Hydroelectric dams: Immediate response to increased demand

Cons of Hydroelectric dams and Tidal barrages

Big impact on surrounding environment

Stop boats and Fish from travelling up or down the river

Initial set up is often expensive

Hydroelectric dams: flood huge areas (habitats)

Wave power

The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy in this movement to drive electricity generators.

Wave Power pros and Cons

Pros:

It is a renewable energy resource and there are no fuel costs

No harmful polluting gases are produced

Cons:

It is difficult to scale up the designs for wave machines to produce large amounts of electricity

Having many wave machines can negatively affect wildlife