Topic 1 - Energy (finished but recheck with sme)

4.1.1 - Energy changes in a system, and the ways energy is stored before and after such changes
4.1.1.1 - Energy stores and systems

The energy stores include:

  1. Thermal energy stores

  2. Kinetic energy stores

  3. Gravitational potential energy stores

  4. Elastic potential energy stores

  5. Chemical energy stores

  6. Magnetic energy stores

  7. Electrostatic energy stores

  8. Nuclear energy stores

Energy is transferred:

  • Mechanically (by a force doing work)

  • Electrically (work done by moving charges)

  • By radiation (light or sound)

When a system changes, energy is transferred:

  •  Energy can be transferred into or away from the system:

    • Between different objects in the system

      •                     OR

    • Between different types of energy stores

  • A system is a fancy word for a single object or a group of objects that you’re investigating/interested in

  • Closed systems are systems where neither matter nor energy can enter or leave

    • The net change in the total energy of a closed system is always zero

Energy can be transferred by doing work:

  • Work done = energy transferred

  • Wok can be done when:

    • Current flows

    • a force moves an object

  • System Examples:

    • The initial force exerted by a person to throw a ball upwards does work

      • Causes an energy transfer from the chemical energy store of the person’s arm to the kinetic store of the ball and arm

    • Friction between a car’s brakes and its wheel does work

      • Energy is transferred from the wheel’s kinetic energy stores to the thermal energy store of the surroundings

    • The normal contact force in a collision between a car and a stationary object does work

      • Energy is transferred from the car’s kinetic energy store to other energy stores(E.P.E and thermal energy)

    • When something is dropped from a height - the gravitational force does work

      • Energy from G.P.E store is transferred to its kinetic energy store

    • The boiling water in a kettle

      • Energy from the kettle’s heating element is transferred to the water’s thermal energy store

4.1.1.2 - Changes in energy

Kinetic Energy stores:

  • Energy is transferred to this store when the object speeds up

  • Energy is transferred away from this store when the object slows down

  • The energy in the kinetic energy store depends on the object’s mass and speed:

    • Equation of kinetic energy:

      • Ek = ½mv2

        • m = mass(kg)

        • v2 = Speed2(m/s2)

Gravitational Potential energy stores:

  • The higher an object, the more energy is transferred to the object’s gravitational potential energy store

  • The energy in an object’s potential energy depends on the object’s mass, its height and the strength of the gravitational field it is in:

    • Equation of gravitational potential energy:

      • Ep = mgh

        • m = mass(kg)

        • g = Gravitational field strength(N/kg)

        • h = height (m)

Elastic potential energy stores:

  • Stretching or squashing an object can transfer energy to its E.P.E store

    • As long as the limit of proportionality isn’t exceeded

  • Equation for E.P.E:

    • Ee = ½ke2

      • k = Spring constant(N/m)

      • e2 = Extension2(m)

4.1.1.3 - Energy changes in systems

Specific heat capacity:

  • Specific heat capacity = the amount of energy needed to raise the temperature of 1kg of a substance by 1oC

  • The amount of energy stored in or released from a system as its temperature changes can be calculated using the equation:

    • ∆ E  = m c  ∆ θ

      • ∆ E = change in thermal energy (Joules)

      • m = Mass (kg)

      • c = Specific heat capacity (J/kgoC)

      • ∆ θ = Temperature change (oC)

4.1.1.4 - Power

  • Power is the rate of energy transfer, or the rate of doing work

  • Power is measured in watts

    • 1 watt = 1 joule of energy transferred per second

    The 2 calculations to calculate power are:

  1. P = E/T

    1. P = Power (w)

    2. E = Energy transferred (J)

    3. T = Time (s)

  2. P = W/T

    1. P = Power (w)

    2. W = Work done (J)

    3. T = Time (s)

  • E.g - a car with a more powerful engine will reach the finish line faster (it will transfer the same amount of energy but over less time as power is the rate of energy transfer and not the amount of energy)

4.1.2 - Conservation and dissipation of energy
4.1.2.1 Energy transfers in a system

(come back to this and do conduction+convection)

Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed

  • Dissipated energy is the energy being stored in a way that is not useful (usually energy has been transferred to thermal energy stores)

  • E.g:

    • When you use your phone, energy is usefully transferred from the chemical energy store from the battery. But some of this energy is dissipated in the form of thermal energy (phone gets hot after a while of using it)

      • Your phone is a system

    • When a cold spoon is dropped into an insulated sealed flask of hot soup, energy is transferred from the thermal energy of the soup to the useless thermal energy of the spoon causing the soup to cool down

      • It is a closed system between the soup and the cold spoons as no energy has left the system - the net energy change = 0

Reducing unwanted energy transfers:

  • Lubricants can be used to reduce the friction between the object’s surfaces when they move so less energy is dissipated as there is less frictional force

  • Thermal insulation can be used to prevent energy losses via heating - for example:

    • Houses have cavity walls - made up of inner and an outer wall with an air gap in the middle

      • The air gap reduces the amount of energy transferred by conduction via the walls

    • Some houses have cavity wall insulation, where the cavity wall air gap is filled up with foam

      • Reduces energy transfer by convection

    • Loft insulation are usually made out of fibreglass wool as it it is a good thermal conductor

      • Reduces energy loss by conduction

      • Prevents convection currents from forming

    • Double-glazed windows have an air gap between 2 sheets of glass to prevent energy transfer by conduction through the windows

    • Draught excluders around doors and windows to reduce energy transfers via convection

  • Some houses have thick walls that are made from a material with a low thermal conductivity

    • The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material

    • Therefore, the thicker the walls and the lower their thermal conductivity, the slower the rate of energy transfer

4.1.2.2 Efficiency

There are two equations to work out Efficiency:

  1. Efficiency = Useful output energy transfer/Total input energy transfer

    1.                                     OR

  2. Efficiency = Useful power output/Total power input

No device is 100% efficient:

  • Electric heaters are an exception as all energy in the electrostatic energy store are transferred to useful thermal energy stores

  • Can increase the efficiency by insulating objects, lubricating them or making them more streamlined

4.1.3 - National and global energy resources

Non-renewable energy = 

  • They will all run out one day

  • They all do damage to the environment

  • But are reliable

  • Fossil fuels:

    • Fossil fuels = natural resources that form underground over millions of years

    • Burnt to provide energy

    • 3 main fossil fuels:

      • Coal

      • Oil

      • (Natural) Gas

  • Nuclear fuels:

    • e.g. - uranium and plutonium

Renewable energy =

  • Will never run out (energy can be replenished as it is used)

  • Most of them do damage to the environment - but less nasty than the non-renewable energy sources

  • Don’t proved as much energy

  • Some are unreliable (depend on weather)

  • Renewable sources are:

    • Solar

    • Wind

    • Water waves

    • Hydro-electricity

    • Bio-fuel

    • Tides

    • Geothermal

Energy resources can be used for transport:

  • Non-renewable energy resources:

    • Petrol and diesel powered vehicles use fuel created from oil

    • Coal is used in some old-fashioned steam trains

  • Renewable energy resources:

    • Vehicles that run on pure bio-fuels or a mix of bio-fuel and petrol/diesel

Energy resources can be used for heating:

  • Non-renewable energy resources:

    • Natural gasses as fuel for heating homes in the UK

      • Gas is used to heat water which is pumped throughout radiators 

    • Coal is burnt in fireplaces

    • Electric heaters use electricity generated from non-renewable resources

  • Renewable energy resources:

    • Geothermal heat pump

    • Solar panels use thermal radiation to heat water

    • Burning bio-fuel

    • Electric heaters use electricity generated from renewable resources

Energy resources can be used for generating electricity:

  • Non-renewable energy resources:

    • Fossil fuels are combusted to heat water to produce steam to turn turbines to generate electricity

    • Nuclear fuels are reacted to heat water to produce steam to turn turbines to generate electricity

  • Renewable energy resources:

    • Wind turns turbines directly to generate electricity

    • Hydro-electric - water is stored at a height then when released rushing water turns the turbines directly to generate electricity

    • Tidal - movement of water due to tides turn turbines directly to generate electricity

    • Geothermal - hot rocks underground used to heat water to produce steam to turn turbines that generate electricity

    • Solar cells use light to generate electricity

    • Water waves - moving water due to waves turn turbines directly to generate electricity

Pros and cons of renewable energy resources:

  • Wind power -

    • Pros:

      • No pollution (a bit when manufactured)

      • No permanent damage to landscape

      • No fuel costs and minimal running costs

    • Cons:

      • Very noisy

      • Effect on scenery

      • Unreliable - turbines stop is wind is too strong or if the wind stops

      • Initial costs are quite high

  • Solar cells -

    • Pros:

      • No pollution

      • Sunny countries find that it is very reliable

      • Minimal running costs

    • Cons: 

      • Can’t increase energy output if demand is high

      • Manufacturing cells produce pollution

      • Can only generate electricity on a small scale

      • Initial costs are high

  • Geothermal -

    • Pros:

      • Reliable - always available and constant energy source

      • Little pollution (gases can be released naturally from the ground)

    • Cons:

      • initial cost is very high

      • Only possible in volcanic areas

  • Hydro-electric -

    • Pros:

      • Immediate response to an increase demand of electricity

      • No fuel costs and minimal running costs

      • Reliable - constant supply of water

      • No pollution

    • Cons:

      • Reservoirs ruin scenery 

      • Loss of habitat

      • Initial costs are high

  • Wave power -

    • Pros:

      • No pollution

      • No fuel costs and minimal running costs

    • Cons:

      • Disturbing the seabed and habitats

      • Hazard to boats

      • Unreliable - waves die out when wind drops

      • Initial costs are high

      • Doesn’t provide energy on a large scale

  • Tidal -

    • Pros:

      • No pollution

      • Reliable (tides happen twice a day without fail)

      • No fuel costs and minimal running costs

      • Has potential to generate significant amount of energy

    • Cons:

      • Altering habitats

      • Initial costs are high

      • Preventing free access by boats

      • Spoiling the view

  • Bio-fuels:

    • Pros:

      • Carbon neutral (burning and growing plants at the same rate)

      • Reliable - crops take a short time to grow and different crops can be grown all year round

      • Cannot respond to immediate energy demands

    • Cons:

      • Cost to refine biofuels so that they are suitable for use is high

      • Could neglect food security (not enough space and water for food crops)

      • Loss of natural habitats for crops

      • Decay of this vegetation produces carbon dioxide

Use of renewables is limited by reliability, money and politics:

  • Scientific evidence do not have enough power to make people, companies or governments change their behaviour

  • Building renewable power plants cost money - so energy provides don’t want to switch considering how cost-effective fossil fuels are

    • Cost of switching will have to paid by customers via bills, via government and taxes

    • People can’t and don’t want to pay therefore it might not be ethical

  • Even if the power plants are built there will be arguments where to put them

    • For instance people don’t want to live next to wind turbines because of noise

    • Research on improving reliability and cost of renewables takes time and money

    • making personal changes are expensiveÂ