energy

What is kinetic energy ?

It’s the energy stored in moving objects

Stationary objects have no kinetic energy

What is the equation for kinetic energy ?

Not given in exam

What happens when A car travels at a constant speed?

Chemical energy store in petrol

Chemical reaction takes place

The energy is converted into kinetic energy store as it moves

What is elastic potential energy ?

When we stretch a spring we’re applying a force to change the length of the spring

This is called doing work

What are we putting in to stretch the spring ?

And what is it?

We’re putting energy in to stretch the spring .

The stretched spring is storing this energy and we call that energy elastic potential energy .

Force applied

It stretches more

Graph for elastic potential energy

At the start extension directionally proportional to force

But if we apply too greater force then its no longer directly proportional it wont return to original length

Calculation for elastic potential energy ?

We are given this

What is gravitational potential energy ?

Is the energy stored in an object due to its position above the earths surface

This is due to the force of gravity acting on an object

An example of gravitational potential energy

A ball on the ground

Now gonna lift it and place it on a shelf

To do this were using the chemical energy store in our muscles and we’re changing this to gravitational potential energy in the ball

If the ball falls of shelf the energy changes to thermal and kinetic

What is the equation for gravitation potential energy ?

Not given at all

How much energy is stored in hot water?

In order to answer this we need to look at the idea of specific heat capacity

What is the specific heat capacity of a substance ?

Is the amount of energy required to raise the temperature of 1kg of the substance by 1 degree

Specific heat capacity equation ?

You are given this in exam

What is the law of conservation of energy ?

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

A pendulum - swings

This is called a system and its an object or group of objects

Closed system

No energy can enter or leave

Pendulum - energy transfers

Pendulum swings

Friction causes energy to be transferred to thermal energy

The fixed point and the air around the pendulum gradually get warmer

These stores of thermal are less useful the energy has been dissipated (wasted)

This will cause the pendulum to gradually swing with less energy and eventually stop

How can we reduce unwanted energy transfers ?

By reducing friction

• use lubricant eg oil on the fixed point

• Remove the air particles from around the pendulum

What happens when a bungee jumper jumps ?

At the start of the jump all of the energy in the system is the store of gravitational potential energy

As the jumper falls energy is transferred from grav pot energy store to kinetic energy store

When the bungee rope just starts to tighten the kinetic energy store is now at its maximum

When the rope is fully extended the kinetic energy store is zero the jumper is not moving - all of the energy has been transferred to the elastic pot energy store

The bungee rope now recoils and the energy is transferred from elastic pot back to kinetic

During ascent energy transfers from kinetic back to grav pot

At the top of ascent all of the energy is now in the grav pot energy store

Does the bungee jumper return back to original position ?

Never, This is bc energy is dissipated as thermal energy

Due to -

• friction with air particles

• Stretching effects in the bungee rope which is not fully elastic

What is work ?

Work is done whenever energy is transferred from one store to another

What are 2 examples of work ?

Mechanical work involves using a force to move an object

Electrical work involves a current transferring energy

An example of mechanical work

Work done equation

Have to learn this

Another example of work done

A car travelling at a speed of 20 metres per second

The driver applies the brakes and the car comes to a stop

A car that is moving has kinetic energy store

So when the driver presses on the brakes the brake presses against the wheel this creates friction between the brake and the wheel

The kinetic energy store of the car is transferred to thermal energy store in the brakes

The tem of the brakes increases and the car slows down and stops

What is power?

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

Equations for power- learn

What is the unit for power ?

1 watt (W) is an energy transfer (or work done) of 1 J per second

2 types of bulbs

Old style bulb

Energy efficient led bulb - popular

Efficiency ?

Tells us what fraction of the energy we put into an appliance is transferred to useful forms of energy

What is the calculation for efficiency - not given

How Can we can increase the efficiency of an energy transfer ?

Pan of hot water example

We want thermal energy to pass from the hob into the water however a lot of the thermal energy is wasted

We’ve got thermal passing into the air around the edges of the hob that are not in contact with the pan

We’ve also got thermal energy passing into the air at the surface of the after we can reduce both of these by using a pan with a wider base and a lid

Both of these reduce unwanted transfer thermal energy

What is the other issue with using a pan to heat water?

A lot of thermal is actually used to heat the base of the pan itself

We can overcome that by placing the heating element inside the water and that’s how an electric kettle works

Pan - metal is a good conductor of heat so thermal will …

- pass thru the sides And the lid of the pan into the air

Plastic conducts heat less well than metal its got a lower thermal conductivity

Looking at the kettle it has plastic walls ans lid and thermal energy is passing into the air and …

Less thermal energy passes thru the walls and lid and into the air so this makes the kettle a more efficient way of heating water than using pan

What is the Overview of the topic cooling of buildings

Poorly insulated building a lot of thermal energy is passing out thru the window and walls

Well insulated building - less thermal energy passing out of building

Factor that affect how quickly a building cools down

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

What two layers are modern houses built from ?

What is between the walls?

• External brick wall

• Internal breeze block wal

  Theres a cavity

The thermal conductivity of walls built is high so a lot of thermal energy can transfer out of the house to correct this …

Builders pack the cavity with an insulating material which has a very low thermal conductivity

Thermal energy can escape thru windows so we need to stop this

Single glazed has high thermal conductivity

Double glazed has low thermal conductivity

Which is better for homes

Double glazed windows

A lot of thermal can pass thru roof so we can reduce this by ..

Having a loft insulation

2 main points of reducing thermal energy from a house

• construct the building using materials with low thermal conductivity

• Build the house with thick walls as this also reduces the rate of thermal energy transfer

What are the Uses of energy ?

Transport

Generating electricity

Heating

What ar the 3 main fossil fuels ?

Coal

Oil

Gas

What are the advantages of fossil fuels ?

Reliable - provide energy when we need it

Releases a great deal of energy

Abundant and cheap

Extremely versatile

What are the disadvantages of fossil fuels ?

• Burning fossil fuels release a huge amount of carbon dioxide

• Fossil fuels are non renewable they are not being replenished

• Fossil fuels can release other pollutants - diesel - carbon particles and nitrogen oxides And coal - sulfur dioxide leads to acid rain

What is a nuclear power ?

Is non renewable

The plants run on the elements uranium and plutonium

Nuclear power advantages ?

Once a nuclear power plant is running it releases no carbon dioxide Therefore nuclear power does not contribute to climate change

Extremely reliable generates lots of electricity when we want it

Nuclear power disadvantages ?

Nuclear power contains highly dangerous radioactive materials if there’s an accident then these materials could be released into the environment

Decommissioning a nuclear power plant takes many years and is very expensive

Nuclear power plants generates large amounts of highly dangerous radioactive waste this must be stored for thousands of years before it’s safe

The uk energy mix -

The uk has abundant reserves of coal. up until the 1950s almost all of the electricity generated in the uk came from burning coal

Coal and coal gas were also used for almost all heating and cooking in the uk

In 1950s nuclear power came online and by the 1980s..

This produced around 20 percent of all the uks electricity

In the 1970s the uk became a major producer of

Oil and gas from the North Sea and this began to replace coal for electricity generation

By 2000 as much electricity was generated from

Burning gas as from burning coal

Switch from coal to gas

Burning gas generates less carbon dioxide than burning coal this contributes less to climate change

Gas fired power stations are flexible they can be switched on quickly during periods of high demand (short start up time) Coal fired power stations have a very long start up time

Switch to renewables

In the 1970s scientists began to realise that carbon dioxide emissions from human activity could be leading to climate change at the time politicians did not see that as a big issue

The problem ws that energy from fossil fuels was very cheap this is an economic factor switching away from fossil fuels costs money and that could cost jobs

In 2005 the Kyoto protocol committed countries to

Reducing greenhouse gas emissions

Does the uk have one of the best locations for widower in the world and did over the last decade the uk open a large number of wind farms ?

yes

Problem with renewables and that’s reliability eg wind speeds can vary and that affects the amount of electricity generated we can address that problem in 2 ways -

• we need a base load ( a constant supply of electricity that’s on all the time ) Nuclear power is ideal for this

• We can use gas fired power stations to provide emergency power in times of peak demand

The future of uk energy

Renewables will provide the bulk of our electricity with nuclear providing a base load and then gas providing electricity during periods of peak demand

What is renewable energy ?

Is one that is being ( or can be ) replenished as it is used

Types of renewable energy resources

Wind power

Solar power

Hydroelectric power

Other extra renewable resource

Tidal power

Biofuels

Geothermal

Wave power

Advantages of renewable energy resources

Never run out of

Do not add carbon dioxide to atmosphere dont contribute to climate change

Disadvantages of renewable energy resources

Wind power and solar power are not reliable some days are not windy and solar power does not work well on cloudy days

Hydroelectric power

Very reliable but habitats are destroyed when dams are built and valleys are flooded

Only useful in countries which have lots of rivers so its not really suitable for uk

Tidal power

Extremely reliable at the moment the uk does not generate any electricity from tidal power

However there are proposals to build a tidal barrage across the Severn estuary but some ppl argue that this would be harmful to wildlife

WAve power

Reliable and has huge potential in the uk which has an extensive coastline

Geothermal energy

Uses heat from earth to generate electricity and heat buildings

Reliable but is not really used much in uk

Petrol car and electric car

The renewable resources so far all generate electricity- A problem bc A lot of energy used in the uk is for transport including cars almost all cars in the uk run on petrol or diesel which are fossil fuels

Where are biofuels produced from?

Are they useful ?

Are produced from plant materials burning biofuels does not add extra carbon dioxide to the atmosphere (carbon neutral)

Biofuels are potentially very useful As we can use them to power vehicles such as cars and buses

If we use land to grow crops for fuel that could push up the price of food