Physics 4.1 - Energy changes in a sysytem, and the ways energy is stored before and after such changes

System

An object or group of objects

What happens when a system changes?

There are changes in the way energy is stored

Closed system

Systems where neither matter nor energy can enter or leave

Ways that energy can be transferred

• heating

• Work done by forces

• Work done when a current flows

When an object is projected upwards how is energy transferred?

If a person throws a ball up, they do work on the ball by accelerating it against the force of gravity. There is an energy transfer from the chemical energy store of the person to the kinetic energy store of the arm to the gpe of the ball.

When a moving object hits an obstacle how is energy transferred?

Energy is transferred because the normal contact force does work on the car. Energy is transferred from the kinetic energy store of the car to the elastic potential and thermal every stores of the object

When an object accelerates how is energy transferred?

The driving force does work. Energy is transferred from the store of the force to the kinetic energy store of the object

When a car slows down how is energy transferred?

The friction between the brakes and wheels does work. Energy is transferred from the wheel's kinetic energy to the thermal energy store of the surroundings

When water is boiled in an electric kettle how is energy transferred?

Energy is transferred by heating. Energy is transferred from the chemical energy store of the kettle to the thermal energy store of the water

Specific heat capacity

The amount of energy needed to raise the temperature of one kilogram of the substance by 1 degree Celsius.

Power

The rate at which energy is transferred or the rate at which work is done

Conservation of energy

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed

Dissipated energy

In a non-enclosed system, dissipated is ‘wasted energy’ that has been transferred to the environment rather than the desired transfer, usually by heating or sound waves

Ways of reducing unwanted energy transfers

• Lubrication reduces friction so less energy is dissipated by thermal energy to the atmosphere

• Insulation reduces the rate of energy transfer by heating.

Methods of thermal insulation

• Cavity walls made of an inner and outer wall with a gap in between of air. The air gap reduces energy transferred by conduction

• Cavity wall insulation with foam has the same effect but also reduces energy transferred by convection

• Loft insulation can reduce convection currents being formed in lofts

• Double-glazed windows work in the same way as cavity walls

• Draught excluders around doors and windows reduce energy transfers by convection

Conduction

The process where vibrating particles transfer energy to neighbouring particles

The higher the thermal conductivity

The higher the rate if energy transfer by conduction across the material

Convection

Where energetic particles move away from hotter to cooler regions

What forms does convection happen in

Liquids and gases

How does thickness of walls effect thermal conductivity

Thicker walls lower the thermal conductivity so the rate of energy transfer will be slower

How does thermal conductivity of walls effect the rate of cooling

The lower the thermal conductivity, the lower the rate of cooling of a building

Can a device be 100% or more efficient

No because some energy is always dissipated

How to increase efficiency

• Thermal insulation

• Lubrication

• Streamlining

The main energy resources available for use on Earth

• Coal

• Oil

• Gas

• Nuclear fuel

• Bio-fuel

• Wind

• Hydroelectricity

• Geothermal

• Tidal

• Solar

• Waves

Fossil fuel examples

• Coal

• Oil

• Natural gas

Renewable energy source

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

Uses of energy resources

• Transport

• Electricity generation

• Heating

Non-renewable energy resources examples

• Fossil fuels

• Nuclear fuel

Renewable energy resources example

• Solar

• Wind

• Water waves

• Hydro-electricity

• Bio-dules

• Tidal

• Geothermal

Which energy resources are used for transport

• Petrol and diesel (from oil)

• Coal for steam trains

• Bio-fuels

• Hybrids

Which energy resources are used for heating

• Natural gas

• Coal

• Electric heaters

• Geothermal

• Solar water heaters

• Burning biofuels

What is wind power

It involves lots of little wind turbines in exposed places like round coasts which rotate a generator

What are the environmental impacts of wind power

• No air pollution

• Visual polution

• Sound pollution

• No permanent damage to the landscape

What are the costs of wind power

Initial costs are high but there are no fuel costs and minimal running costs

Reliability of wind turbines

They rely on the wind, when the wind stops or is too high they stop spinning and don’t produce electricity and it is impossible to increase supply when theres extra demand

What is solar energy

Solar cells generate electric currents directly from absorbing

Environmental impacts of solar energy

• No pollution

• Require quite a lot of energy to set up in the first place

Costs of solar energy

Initial costs are high but after that energy is free and running costs are almost 0

Reliability of solar energy

Very reliable in sunny countries but only in the daytime

What is geothermal power

In volcanic areas or where rot rocks lie near the surface, energy can be harnessed

Environmental impacts of geothermal power

• Almost none

Costs of geothermal energy

Basically free but the costs of building a power plant is high

Reliability of geothermal power

Reliable but there aren’t many suitable locations for power plants

What is hydro-electric power

It uses falling water by building a dam and allowing water out through turbines

Environmental impact of hydro-electric power

• No pollution

• Flooding

• Loss of habitat for some species

• Visual pollution

Cost of hydro-electricity

Initial costs are high, but there are no fuel costs and minimal running costs

Reliability of hydroelectric power

VEry reliable except in times of drought. Can provide an immediate response to an increased demand for electricity.

What is wave power

Lots of little wave powered turbines are located around the coast. The moving turbines are connected to a generator

Environmental impact of wave power

• No pollution

• Disturbs the seabed and habitats of marine animals

• Visual polluion

• Hazard to boats

Costs of wave power

Initial costs are high, no fuel costs and minimal running costs

Reliability of wave power

Very unreliable since waves die out when wind drops. Never likely to provide energy on a large scale.

What is tidal energy

Tides are used by building tidal barrages, big dams built across river estuaries with turbines in them. As the tide comes in it fills up the estruary. Then water is allowed out the estuary at controlled speeds.

Environmental impacts of tidal barrages

• No pollution

• Prevents free access by boats

• Visual pollution

• Alters the habitat of wildlife

Costs of tidal energy

Initial costs are moderately high, but there are no fuel costs and minimal running costs

Reliability of Tidal energy

Pretty reliable as tides happen twice a day without fail and can be predicted. Only work at certain times though.

What are bio-fuels

Biofuels are renewable energy resources created from plant products or animal dung. They can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same way as fossil fuels.

Environmental impact of bio-fuels

• They are supposedly carbon neutral but there is some debate around this

• In some regions, large areas of forest have been cleared to grow bio-fuels, resulting in lots of species losing their natural habitat

• The decay and burning of this vegetation also increases co2 and methane emissions

Costs of bio-fuels

The costs to refine bio-fuels are very high

Reliability of bio-fuels

They are fairly reliable, as crops take a relatively short time to grow and grow all year round. But they can’t respond to immediate energy demands, to combat this, crops are stored for when needed.

What are fossil fuels

Organic matter compressed under sediment at high pressure and temperatures

Environmental impact of fossil fuels

• Burning fossil fuels release co2 into the atmosphere, which add to the greenhouse effect and contribute to global warming

• Due to sulphur impurities, sulphur dioxide can also be produced which causes acid rain, but this can be reduced by removing sulphur

• Coal mining makes a mess of the landscape and destroys habitats

• Oil spills cause serious environmental problems, effecting the natural life around them

Costs of fossil fuels and nuclear power

While the set-up costs of power plants can be high in comparison to others, the running costs aren’t that expensive. They are relatively cost-effective

Reliability of fossil fuels and nuclear energy

Fossil fuels and nuclear energy are reliable. There is enough of them to meet current demand, and they are extracted at the same rate that power plants need them. However, they are finite resources and will one day run out.

What is nuclear energy?

Energy released due to nuclear fission

Environmental impacts of nuclear energy

• Nuclear power is clean

• Nuclear waste is very dangerous and very difficult to dispose of

• Always the risks of major catastrophes like chernobyl

Costs of nuclear power

Nuclear fuel is relatively cheap but the overall costs of nuclear fuel are much higher due to the costs of power plants and final decommisioning

Why is the use of renewable energy limited

• Reliability - renewable energy is less reliable

• Money - building new power plants is expensive, and people making individual changes need lots of money to invest in renewable energy sources

• Social - there are arguments over where to put these new energy sources

• Political