Energy P1

8 energy stores

Thermal (heat energy - temperature)

Chemical (energy in chemical bonds)

Kinetic (movement/ motion)

Magnetic (energy holding magnets together)

Elastic (energy stretched spring)

Gravitational potential (energy position gravitational field)

Electrostatic

Nuclear (energy breaking atoms apart)

4 energy transfers

Mechanically (physical with force)

Electrically (current/plugging socket)

Radiation (light/sound waves)

Heating

Law of conservation of energy

Energy is never created or destroyed only transferred between different objects and forms

Example conservation of energy- phone

1) Plug phone in wall electrical energy travel along wire

2)Transfer to chemical energy store in battery

3) When use phone chemical energy convert back to electrical energy

4)Flows around circuit and powers parts

5) To see screen electrical energy convert to light energy

6)For speaker convert to sound energy

7) Some energy is dissipated as waste (usually heat)

Open system

Matter of system can exchange with outside environment to gain/ lose energy

Closed system

Matter of system cannot exchange with outside environment so energy cannot leave or enter (energy is transferred within system with overall change zero)

2 types of work done (=energy transferred)

Mechanically (a force moving an object)

Electrically (current flowing in circuit)

Kinetic energy

Energy possessed due to motion, amount depends on speed and mass of object. Faster= more kinetic energy or More mass=more kinetic energy

Kinetic energy equation

Kinetic energy (J)= ½ x mass (kg) x velocity squared (m/s)

Gravity and factors affecting strength

Gravity = force of attraction between objects with mass

Gravitational potential difference= how strong the pull of gravity is at specific location

Size of force depends on: Mass of object (larger mass= stronger pull). Distance apart (further away= weaker pull)

Gravitational field strength values

On earth: 9.8 N/kg

On moon: 1.6 N/kg (smaller mass)

Mass

Property of an object (amount of matter inside). Stays same everywhere

Weight

The force acting on an object due to gravitational field strength. Changes depending on planet

Weight equation

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

Gravitational potential energy

The energy stored by an object lifted up against the force of gravity

Gravitational potential energy equation

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

Energy changes in a system (rollercoaster): ideal conditions

Object falling- energy transferred mechanically from GPE store to KE store

Object rising- energy transferred mechanically from KE store to GPE store

No friction or air resistance means GPE lost= KE gain or KE lost= GPE gain

Energy changes in a system (rollercoaster) : Real world conditions

Work is done against friction and air resistance

Small amounts energy dissipated (wasted) to surroundings and transferred into thermal energy store of wheels, tracks and air

Object less LE and lower speed than calculated

Internal energy

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

Kinetic energy is the main energy store in particles

How heating temperature affects particles and temperature

Heating transfers energy to kinetic energy stores, this increases internal energy of the system

Temperature is a measure of average kinetic energy of particles (more internal energy= higher temperature)

Specific heat capacity

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

For cooling: amount of energy raised as 1kg of a substance cools by 1 degree

Specific heat capacity equation

Change in internal energy (J)= mass (kg) x specific heat capacity (J/kg degrees) x change in temperature (degrees)

Specific heat capacity: Real world conditions

Some thermal energy is lost to surroundings, temperature will not rise as much as calculated

Reduce this- put a lid on container and insulate sides to reduce unwanted heat transfer

Reducing heat loss: stopping conduction

Thick walls with low thermal conductivity

Cavity walls filled with insulating foam (trapped air bubbles)

Double glazed window with narrow air gap (stop heating directly passing through solid)

Reducing heat loss: stopping convection

Foam seals around doors and windows (prevent warm air out of room)

Thick curtains across windows (stop energy escaping through convection currents)

Conduction

Particles at hot end gain kinetic energy, vibrate faster and collide with neighbouring particles more often so they pass on kinetic energy from hot end to cooler end.

Happens mainly in solids as particles are tightly packed together (easier to collide)

Thermal conductivity

Measure of how quickly a material conducts heat

Metals have high thermal conductivity (heats up faster)

Non-metals have low thermal conductivity (heats up slower)

Insulator

Material that doesn’t conduct heat well (low thermal conductivity) e.g plastic sleeve on drink prevents heat escaping (keep warm) and protect hands

Convection

Fluid particles heated, gain kinetic energy and move faster, so spread apart and become less dense. Less dense heated fluid rises above cooler denser fluid, then cools down causing them to sink again (convection current cycle)

Happens in fluids as heat energy is transferred by moving positions rather than just vibrating (in solids)

Radiation

Heat energy transfer through infrared waves without any particles, all objects absorb and emit radiation constantly

Hotter objects emit more radiation than they absorb

Cooler objects absorb more radiation than they emit

Friction

Resistance an object encounters when moving over a solid/ through a liquid, reducing the efficiency of energy transfers and cause objects to heat up

Methods to reduce friction

Adding oil/ lubricants (parts slide smoothly against each other)

Streamlining cars/planes (reduce friction from air resistance)

Less fuel used as system more efficient

Power

The rate at which energy is transferred (e.g electrically to a phone)

The rate at which work is done (e.g mechanically pushing a car)

Power equations

Power (w)= energy transferred (J) / time (s)

Power (w)= work done (J) / time (s)

Efficiency

The proportion of energy supplied that is transferred into useful energy output

Efficiency equation

Efficiency= useful energy output / useful energy input

Efficiency= useful power output / useful power input

Effeciency for devices

No device is 100% efficient as they all waste some energy that is dissipated as thermal (heat) energy

A few devices (electric heaters) 100% efficient as intended function is to produce thermal energy (wasted heat counts as useful output)

Non- renewable and energy resources

Energy resources that cannot be replenished as it is used (finite-limited amount)

Coal, oil, natural gas (fossil fuels), nuclear

Renewable and energy resources

Energy source being replenished as it is used

Hydroelectric, geothermal, solar, wind, biofuels, tidal

Reliable

Produce energy irrespective of conditions e.g weather

Trends in energy resources

Past- almost completely reliant on non- renewable fossil fuels

Current/ future- Increased use of biofuels and electricity (e.g electric cars and solar water heaters)

To reduce environmental impact- lowering CO2 emission and climate change

Status of electricity as a resource

Neither renewable or non- renewable as depends how it is generated (e.g wind turbine or coal)

80% of global electricity is non- renewable

Uses of energy resources

Transport- fuelling cars, trains, planes ships (petrol, diesel and kerosene)

Domestic- warming homes and cooking food (natural gas)

Electricity generation

Fossil fuel pros and cons

Pros- relatively cheap, reliable, national grid infrastructure designed for them

Cons- finite resource, produce CO2 (green house gas + causes climate change), produce toxic gas e.g sulfur dioxide to cause acid rain

Nuclear power pros and cons

Pros- Reliable, no pollutants produced, higher energy density transferred per kg than fossil fuels

Cons- finite resource, quite expensive, produce radioactive waste

Wind power

Converts kinetic energy from moving air into electrical energy using a generator, placed in exposed areas like coasts or hills

Solar power

Directly generates electrical currents from sunlight, used in low energy devices (watches/calculators) and remote regions not connected national grid

Wind/ Solar power pros and cons

Pros- renewable, no pollutants produced, low running costs

Cons- unreliable, high upfront costs, no supply control when peak demand, visual/noise pollution

Geothermal power

Thermal energy stored in hot rocks underground

Direct heating use- pumping cold water into ground and back up to heat directly for homes (cheaper)

Generate electricity- water turns into steam to spin a turbine to drive a generator (more expensive)

Geothermal power pros and cons

Pros- renewable, reliable over long periods, no pollutants produced, little damage to environment

Cons- only use in certain areas (volcanic regions), power plants expensive to build

Biofuels

Fuels made from recently living organisms (animal waste or plants)

Plants absorb CO2 through photosynthesis when growing the release same amount of CO2 when burned for fuel so net zero release or CO2 atmosphere (carbon neutral)

Biofuel pros and cons

Pros- renewable, reliable, relatively cheap, easy to transport, mix directly with fossil fuels in normal cars

Cons- massive space to grow crops (deforestation/ loss of habitats), harvesting/processing/ transporting still releases CO2 from machinery

Hydroelectric and Tidal

A massive dam to prevent water flowing naturally, creating a difference in water levels leaving a higher water level on one side

Hydroelectric- traps water moving downstream from an upstream reservoir

Tidal- traps water in an estuary as the tide comes in due to moons gravity

Hydroelectric and tidal energy transfers

Trapped high level water has huge amount of gravitational potential energy, as water is released the falling water transfers energy to kinetic store of the turbines, rotating turbines spin generators to generate electricity

Hydroelectric/ Tidal pros and cons

Pros- renewable, reliable sources, no pollutants produced, low running costs, work on large and small scales. Hydroelectric pro- release water instantly when high demand

Cons- high upfront cost, affects fish migration/ boats travelling, impacts surrounding environment (habitat/wildlife). Hydroelectric pro- flood huge areas