# Conservation of energy 3.1-3.14

Follows specification

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## Change in GPE - 3.1

Change in gravitational potential energy (Joules,J) = mass (kg) x gravitational field strength (N/kg) xchange in vertical height (m)

⏏GPE = M x G x ⏏H

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## Energy associated with moving object

Kinetic energy (J) = 1/2 x mass (kg) x speed2 (m/s)

KE = 1/2 x m x v2

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## Conservation of energy 3.4

The law of conservation of energy

• Energy cannot be created of drestroyed, it can only be transferred from one store to another.
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## Systems and energy 3.5

• A system is a portion of the universer chosen for analysis - it can be anything
• In analysing the energy transfers within system, we talk about energy stores and energy pathways.

An object accelerated by a constant force:

• Work is done by a force on an objects. This work is converted to the objects kinetic store.

An object projected upwards:

• The objects energy is initially in the kinetic store as it moves upwards. The objects energy is slowly transferred from the kinetic store to the gravitational potential store as it slows down and climbs higher. Once the object reaches its highest point, all of its energy is in the gravitational potentional store. As the object falls again, energy transfers from the gravitational potential store to the kinetic store.

A vehicle slowing down:

• To begin with, the wehicles energy is kinetic store, the brakes do work slowing down the car. During this process, energy is lost through heat and sound.

A moving object hitting a car:

• The objects energy is in the kinetic store at the start because it is moving. When the object collides with the obstacle, energy is converted to the  kinetic store if the object (making it move) , the thermal store of the object and obstacle ( the particles in the object and obstacle vibrate more). Some energy remains in the objects kinetic store as i moves away after the collision.

Bringing water to the boil:

• Energy transfers from the electrical store of the mains power suply to the thermal store of the water.

Types of energy stores

• Chemical →in food, fuel and electri batteries
• Kinetic → in moving objects
• Gravitational→ in objects raised above the planets surface
• Elastic→In a streched, compressed or twisted object
• Thermal→In any heated object
• Magnetic→in any object with a magnetic field
• Electrical→in any electrostatic forces between charges
• Nuclear→the forces between aomic nuclei

Force pathways include

• Mechanically → when a force acts and an object moves
• Electrically→ when and electric curent flows
• Heating→ a temperature differences between bjecs
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## Energy stores and pathways

Types of energy stores

• Chemical →in food, fuel and electri batteries
• Kinetic → in moving objects
• Gravitational→ in objects raised above the planets surface
• Elastic→In a streched, compressed or twisted object
• Thermal→In any heated object
• Magnetic→in any object with a magnetic field
• Electrical→in any electrostatic forces between charges
• Nuclear→the forces between aomic nuclei

Force pathways include

• Mechanically → when a force acts and an object moves
• Electrically→ when and electric curent flows
• Heating→ a temperature differences between bjecs
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## Energy transfers in a closed system - 3.6

For any system the total energy input will equal the total energy output (although some of this will be useful and some will be wasted), so there is no net change in the total energy in that system.

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## Wasteful mechanical process - 3.7

Mechanical process → Concerned with machines or machinery , relating to physical forces

In any energy transfer, some nergy will be dissipated as thermal energym therefore heating its surrounding.

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## Wasted energy - 3.8

• Lost energy spreads out and is lost to the surroundings. It is very hard to reuse, this is why we should be mindful not to waste energy.
• for example a lamp→ designed to change electrical energy into light energy.
• some is wasted in the form of heat→ ALL electrical devices waste energy through heat
• if you can here the lamp buzzing, it is wasting energy through sound too
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## Reducing wasted energy - 3.9

• Lubrication ( through oil of grease for example) reduces friction between moving parts and hence the transfer of thermal energy. This means that a greater proportion of the total input is transferred as useful energy.
• Thermal insulation reduces the transfer of thermal energy through conduction convection and radiation.
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## Thermal insulation - 3.10

• The thicker the wall the lower the rate of thermal energy is transferred away from the building .
• The lower the thermal conductivity of the material, the lower the rate at which thermal energy is transferred away from the builing.
• good thermal conductors tranfer thermal energy more quickly.
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## Efficiency - 3.11

efficiency = useful energy / total energy supplied to the device

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## Increasing efficiency - 3.12

• Reducing friciton through lubrication for example, reduces the energy transferred as thermal energy (wasted energy)
• therefore, there is more useful energy output for the same total energy input and so the energy transfer is more efficient
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## Main energy sources - 3.13

Renewable energy

• solar
• hydropower
• biomass
• geothermal
• wind

non-renewable energy

• oil
• coal
• nuclear
• natural gas
EnergyEnergy storeRenewable or non-renewableUsesPower outputImpact on environment Fossil fuels (oil, coal and natural gases) Chemical Non-renewable Transport, heating, electricity generation High Releases CO2 (causes global warming) Nuclear fuels Nuclear Non-renewable Electricity generation Very high Radioactive waste (needs to be disposed of safely) Biofuel Chemical Renewable Transport, heating, electricity generation Medium Carbon-neutral so low impact Wind Kinetic Renewable Electricity generation Very low Take up large areas that could be used for farming, people say windmills spoil their view Hydroelectricity Gravitational potential Renewable Electricity generation Medium Local habitats are affected by the large areas that need to be flooded to build dams Geothermal Internal Renewable Electricity generation, heating Medium Very low Tides Kinetic Renewable Electricity generation Potentially very high but hard to harness Tidal barrages can block sewage which needs to go out to sea Sun Nuclear Renewable Electricity generation Potentially very high, but hard to harness Very little Water waves Kinetic Renewable Electricity generation Low Very low
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## patterns and trends - 3.14

Explain pattern and trends in the use of energy resources

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