GCSE Physics: Energy (Topic 1)

What is kinetic energy?

• The energy an object has due to it motion (movement) e.g. runners, buses and comets

What are energy stores ?

• when energy is transferred to an object the energy is stored in one of the objects energy stores

What are the energy stores?

8 energy stores:

• Thermal → total energy of its particles due to their kinetic energy (movement) & potential energy (position)

• Kinetic

• Gravitational Potential

• Elastic Potential

• Chemical→ energy stored in the bonds of chemical substances e.g. fuel , food etc

• Magnetic→ when magnetic materials in a magnetic field

• Electrostatic→ When 2 charged objects are near each other & interact via electric fields

• Nuclear→ stored in necleus of atom due to the strong nuclear forces holding it together

What is a stationary object?

• An object that’s not moving → has 0 speed & velocity

• Has NO kinetic energy → “stationary ”→ at “Rest ”

What is the equation for kinetic energy?

• Ek= ½ mv²

• Kinetic energy-Ek-measured in Joules, J

• Mass-m-measured in kg

• Speed-v-measured in m/s

-to become Kilojoules (kJ) → divide J by 1000

-1kJ = 1,000J

What is elastic potential energy?

DEF:

• The energy stored in a stretched or compressed spring

• Work(applying a force) is done when a spring is stretched or compressed→change length e.g.rubber bands, compressed springs, inflated balloons.

What is the equation for elastic potential energy?

• Ee= ½ke²

• Elastic Potential energy-Ee-measured in Joules, J

• Spring constant-k-measured in N/m

• Extension-e- measured in metres

• The force applied (to extend an object) and the extension is directly proportional until the limit of proportionality has been exceeded.→ if exceeds past limit of proportionality the object wont return back t original state

What is gravitational potential energy?

• The energy stored in an object due to it’s position in a gravitational filed → above the Earth’s surface. e.g. aeroplanes, kites, mugs on a table

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

What is the equation for gravitational potential energy?

• Ep=mgh

• Gravitational potential energy-Ep-measured in Joules, J

• Mass-m-measured in kg

• Gravitational field strength-g-measured in N/kg

• Height-h- measured in metres

What is specific heat capacity?

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

• Different materials have different specific heat capacities

What is the equation for specific heat capacity?

∆E = m c  ∆ θ

Change in thermal energy- ∆ E- measured in Joules, J

Mass-m-measured in kg

Specific heat capacity-c-measured in J/kg °C

Change in temperature-∆ θ-measured in °C

REQUIRED PRACTICAL: Specific Heat Capacity

(How hard it is to heat something up)-to determine SH capacity of 1/more materials

(IF THE BLOCK—>wrap it in insulating layer)

1. Investigate a solid material (e.g copper) , a block of the material with 2 holes in it for the heater & thermometer to go into is needed

2. Measure the mass of the block using a balance , then wrap it in an insulating layer (e.g thick layer of newspaper) to reduce the energy transferred from the block to the surroundings.Insert the heater & a thermometer

3. Measure the initial temperature of the block using a thermometer , then connect the heater to a power supply , ammeter , and voltmeter.

4. Use the power supply to Set the potential difference , to 10 V. Turn on the power supply and start a stopwatch

5. When you turn on the power , the current in the circuit (i.e the moving charges) works on the heater , transferring energy electrically from the power supply to the heaters thermal energy stores by heating→causing the materials temperature to increase

6. As the block heats up, use the thermometer to measure it’s temperature e.g every minute..Keep an eye on the ammeter→ the current through the circuit , I ,should remain constant

7. When theres enough readings around 10 -. Turn off power supply

8. Now complete some calculations t find materials specific heat capacity :

   • Calculate power supplied →. E= Pt → (t = time in sec)

   • Find Specific heat capacity →∆E = m c  ∆ θ

9. Can plot a graph of energy transferred to the thermal energy store of the block against temperature→ can find the gradient of straight part of graph → ∆ θ / ∆ E

10. Can repeat this experiment with different materials to see how their specific heat capacities to compare

What is thermal energy?

The energy stored due to an objects temperature

The total internal energy due to kinetic energy of its particles (cos they are moving ) & their potential energy (due to postions)

What is the law of conservation of energy?

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

What is a system?

An object or a group of objects.

In which system can no energy enter or leave?

Closed system

Describe energy transfers in a pendulum.

• When the pendulum swings up as high as it can, the gravitational potential energy is at it’s maximum and the kinetic energy is at it’s minimum.

• When the pendulum swings down to it’s lowest point, the gravitational potential energy is at it’s minimum and the kinetic energy is at it’s maximum.

• When the pendulum swings as high as it can in the other direction too, the gravitational potential energy is at it’s maximum and the kinetic energy is at it’s minimum.

What is the problem with the energy transfers in the pendulum?

Some energy is lost to the surroundings It doesn’t consider friction.

Where does friction cause energy to be transferred into less useful stores in the pendulum scenario?

• There’s friction in the fixed point

• There’s friction as the pendulum passes through air particles

• This causes energy to be transferred to thermal energy in these two positions.

• These stores of thermal energy are less useful. The energy has been dissipated (wasted).

Describe ways to reduce unwanted energy transfers.

(blue refers to pendulum)

• lubrication (on the fixed point)

• thermal insulation

• (remove the air particles from around the pendulum)

What is a lubricate and describe

-It’s a method of reducing unwanted energy transfers → friction

a lubricant→ e.g. oil / grease → to lubricate the surfaces & allow them to slide smoothly over each other → reducing friction → less energy is dissipated as heat

Ways of thermal insulation

• Cavity walls →Walls made from two layers → Foam is injected between the inner & outer walls of a house → reduces conduction & convection→ foam traps air → is a poor conductor

• Loft insulation (low thermal conductivity) → thick layer of fibreglass in loft → reduces convection currents in roof space → air trapped in fibres reduces conduction

• Double-glazed windows (low thermal conductivity)→ 2 glass panes with air gap → air/ vacuum is a good insulator, reducing conduction & convection

What is the relationship between thermal conductivity and the rate of energy transfer by conduction across a material?

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

Describe energy transfers in a bungee jumper

• At the start of the jump, all of the energy in the system is stored in the gravitational potential energy.

• As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store

• When the bungee rope just starts to tighten, the kinetic energy store is now at it’s maximum.

• When the rope is fully extended, the kinetic energy store is zero. The jumper is not moving

• The bungee rope now recoils, and energy is fully transferred from the elastic potential energy store back to the kinetic energy store.

• During the ascent, energy transfers from the kinetic energy store back to the gravitational potential energy store.

• Finally, at the top of the ascent, all of the energy is now in the gravitational potential energy store.

  • Key points:

  • The jumper never returns to its original position because energy is dissipated as thermal energy (due to friction with air particles and also due to stretching effects in the bungee rope which isn’t fully plastic).

What is power?

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

What are the equations for power?

Power (W) = Energy transferred (J)/time (s)

Power (W)= Work done (J)/time (s)

What does the unit Watt mean?

watt= joule per second

What does efficiency mean?

The proportion of useful energy output over total energy input.

What are the equations for efficiency?

Efficiency= Useful output energy transfer/Total input energy transfer

Efficiency= Useful power output/Total power input

What are non-Renewable & Renewable Energy?

Non renewable = Energy sources that will out one day → fossil & nuclear fuels

Renewable= Energy sources that will never run out

What are the 3 main fossil fuels?

• Coal

• Oil

• Gas

Advantages of fossil fuels

• They’re reliable

• They release huge amounts of energy

• They’re abundant

• They’re versatile (as we can use it for generating electricity, heating transport etc)

Disadvantages of fossil fuels

• Burning fossil fuels release huge amounts of CO2 which contributes to climate change

• Non-renewable (not being replenished as we use them)

• Burning fossil fuels can release other pollutants

Nuclear power - non-renewable

• Non renewable

• Nuclear power plants run on the elements uranium and plutonium

What are the advantages of nuclear power?

• It doesn’t release carbon dioxide so doesn’t contribute to climate change.

• Extremely reliable-it generates a lot of electricity exactly when we want it.

What are the disadvantages of nuclear power?

• Non renewable

• Nuclear power plants contain highly dangerous radioactive materials. If there’s an accident then these materials could be released into the environment which could be potentially disastrous.

• Decommissioning a nuclear power plant (after the end of it’s life) takes many years and is extremely expensive.

• A nuclear power plant generates large amounts of highly dangerous radioactive waste. This must be stored for thousands of years before it’s safe.

Describe the UK’s old energy mix

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

What two changes happened which meant that the use of coal in the UK fell sharply?

• In the 1950s, nuclear power came online and by the 1980s this produced around 20% of all the UK’s electricity

• In the 1970’s 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 coal.

Describe impacts of switching from coal to gas

• Burning gas generates less carbon dioxide that burning coal. This contributes less to climate change.

• Gas-fired power stations are flexible. They can be switched on quickly during periods of high demands- they have a short start-up time whereas coal-fired power stations have very long start-up time.

Describe the shift to renewable power in the UK

• 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 really see that as a big issue.

  • Energy from fossil fuels was very cheap. Switching away from fossil fuels costs money and that could cost jobs.

• In 2005, politicians began to take climate change seriously and a lot of countries signed up to the Kyoto protocol which committed countries to reducing greenhouse gas emissions

Fact about UK and wind power

• The UK has one of the best locations for wind power in the world. Over the last decade, the UK has opened a large number of windfarms.

• However, wind power isn’t reliable so we need a baseload or we can use gas-fired power stations to provide emergency power in times of peak demand.

What is a baseload?

A constant supply of electricity that’s on all the time.

(nuclear power is ideal for this)

The future of UK energy

• Renewables will provide the bulk of our electricity

• Nuclear will provide a base-load

• Gas will provide electricity during periods of peak demand.

What is the magnetic energy energy store?

• The energy stored when repelling poles have been pushed closer together when attracting poles have been pulled further apart.

• Examples: fridge magnets, compasses, maglev trains which use magnetic levitation

What is internal/thermal energy?

• The total kinetic and potential energy of the particles in an object, in most cases this is the vibrations- which is also known as the kinetic energy of particles. In hotter objects, the particles have more internal/thermal energy and vibrate faster.

• Examples: Human bodies, hot coffees, stoves or hobs. Ice particles vibrate slower, but still have energy.

What is chemical energy?

• The energy stored in chemical bonds e.g. intermolecular forces.

• Examples: foods, muscles, electrical cells.

What is electrostatic energy?

The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart.

Examples: Thunderclouds, Van De Graaff generators

What is nuclear energy?

• The energy stored in the nucleus of an atom.

• Examples: uranium nuclear power, nuclear reactors.

The changes in energy stores when an object is projected upwards.

• When an object is projected upwards, such as a ball, it will initially have kinetic energy. As the object rises higher into the air, the kinetic energy will be transferred to gravitational potential energy. The energy is transferred mechanically. (OR work done by forces)

What are The changes in energy store when a moving object hits an obstacle?

energy shifts from kinetic store of object to the thermal energy of the object and obstacle.

It’s mechanically transferred. (OR work done by forces)

What are The changes in energy store when an object is accelerated by a constant force?

an object accelerated by a constant force e.g. car accelerating energy shifts from chemical store of the fuel to the kinetic store of the object via the mechanical pathway (OR work done by forces)

What are The changes in energy store of a vehicle slowing down?

energy shifts from the kinetic store of the vehicle to the thermal store of the brakes and surroundings via the mechanical pathway (OR work done by forces)

What are The changes in energy store when bringing water to a boil in an electrical kettle?

energy shifts from chemical store of the fuel (at power station) to the thermal store of the water via the electrical pathways (OR work done when a current flows).

What are energy resources used for?

Transport and heated

Transport- non renewable resource

• Petrol and diesel powered vehicles (including most cars) use fuel created from oil.

• Coal is used in some old-fashioned steam trains to boil water to produce steam.

• Electricity can also be used to power vehicles e.g. trains and cars. This can be generated using renewable and non-renewable energy resources.

Transport- renewable energy resources

• Vehicles that run on pure bio-fuels or a mix of biofuels and petrol or diesel. Only the bio-fuel bit is renewable though but it still reduces reliance on non-renewable energy sources.

• Electricity can also be used to power vehicles e.g. trains and cars. This can be generated using renewable and non-renewable energy resources.

Heating- non renewable energy sources

• Natural gas is the most widely used fuel for heating homes in the UK. The gas is used to heat water, which is then pumped into radiators throughout the home.

• Coal is commonly burnt in fireplaces.

• Electric heaters (storage heaters) use energy from non-renewable energy sources.

Heating- renewable energy sources

• A geothermal (or ground source) heat pump uses geothermal energy resources to heat buildings.

• Solar water heaters work by using the sun to heat water which is then pumped into radiators in the building.

• Burning bio-fuels or using electricity generated from renewable energy sources can also be used for heating.

What are the renewable energy sources?

• The Sun (solar)

• Wind

• Water wave

• Hydro electricity

• Bio fuel

• Tides

• Geothermal

Advantages of bio-fuels

• Reliable- as crops take a relatively short time to grow and different crops can be grown all year round. However they cannot respond to immediate energy demands so to combat this, bio-fuels are continuously produced and stored for when they are needed.

• They are supposedly carbon neutral, although there is some debate about this as it’s only true if you keep growing plants at the rate you’re burning this.

Disadvantages of bio-fuels

• Cost to refine bio-fuels so they are suitable to use is very high.

• Some people worry that growing crops specifically for bio-fuels will mean there isn’t enough space or water to meet the demands for crops that are grown for food.

• In some regions, large areas of forest have been cleared to make room to grow bio-fuels, resulting in lots of species losing their natural habitats. The decay and burning of this vegetation also increases CO2 and methane emissions.

Advantages of wind power

-Each turbine has a generator inside that rotates blades turning the generator & producing electricity

• No pollution → except for a bit when they’re manufactured

• Initial costs are high → but there are no fuel costs and minimal running costs.

• There’s no permanent damage to the landscape- if you remove the turbines, you remove the noise and the view returns to normal.

How can a bio-fuel be carbon neutral?

If the amount of CO2 it released by burning it into the atmosphere is equal to the amount absorbed by the plant to make the bio-fuel.

Advantages of hydroelectricity

• No problem in reliability- except in times of drought

• Can provide an immediate response to an increased demand for electricity

• Although initial costs are high, there are no fuel costs and minimal running costs.

Disadvantages of hydroelectricity

• Only suitable in countries which have lots of rivers.

• Habitats are destroyed when dams are built.

• Usually requires the flooding of a valley in order for a dam to be built.

Disadvantages of wind power

• They spoil the view→ need about 1500 wind turbines to replace 1 coal-fired power station and 1500 of them cover a lot of ground which would have a big effect on scenery.

• Can be very noisy → can be annoying for people living nearby.

• Unreliable as it depends on the wind→Turbines stop when wind stops or if wind is too strong → impossible to increase supply when extra demand.

Advantages of geothermal

• Reliable

• Few environmental problems

• Energy can be used to generate electricity or to heat buildings directly.

Disadvantages of geothermal

• Can only take place in volcanic areas

• Cost of building a power plant is often high compared to the amount of energy that it produces.

Advantages of tidal

• No fuel costs and minimal running costs

• No pollution

• Reliable as tides happen twice a day and always near predicted height.

Disadvantages of tidal

• Preventing free access by boats.

• Spoiling the view.

• Altering the habitat of the wildlife e.g. sea creatures that live in the sand.

• If the height of the tide is low then less energy will be provided.

Advantages of solar

• No pollution from the solar cells

• Very reliable in sunny countries-during the day.

• Running costs are very low.

Disadvantages of solar

• Can be unreliable as some days are cloudy.

• Can’t increase the power output when there’s higher demand.

• Factories cause some pollution when manufacturing the cells

• Initial costs are high.

Advantages of wave power

• No fuel costs and minimal running costs.

• No pollution.

• Can be useful on small islands.

Disadvantages of wave power

• Disturbs the seabed

• Disturbing the habitat of marine animals.

• Spoiling the view

• Hazard to boats.

• Unreliable as waves die out when wind drops.

• Initial costs are high.

Advantages of renewable energy resources

• Never run out

• Once in place they do not add any carbon dioxide to the atmosphere- they don’t contribute to climate change.

How can acid rain be reduced when burning oil or gas?

• By removing the sulfur before burning the fuel.

• Cleaning the sulfur dioxide emissions.