Section 4: Energy resources and energy transfera) Unitsb) Energy transferc) Work and powerd) Energy resources and electricity generation

a) Units4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), watt (W).

b) Energy transfer4.2 describe energy transfers involving the following forms of energy: Thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)4.3 understand that energy is conserved4.4 know and use the relationship:

Efficiency = Useful energy outputTotal energy output

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams4.6 describe how energy transfer may take place by conduction, convection and radiation4.7 explain the role of convection in everyday phenomena4.8 explain how insulation is used to reduce energy transfers from buildings and the human body.

c) Work and power4.9 know and use the relationship between work, force and distance moved in the direction of the force:

work done (J) = force (N) × distance moved (m)W = F × d

4.10 understand that work done is equal to energy transferred4.11 know and use the relationship:

gravitational potential energy = mass × g × heightGPE = m × g × h

4.12 know and use the relationship:

kinetic energy = 12 × mass × speed2

KE= 12 mv2

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work4.14 describe power as the rate of transfer of energy or the rate of doing work4.15 use the relationship between power, work done (energy transferred) and time taken:

Power = Work doneTime taken

d) Energy resources and electricity generation4.16 describe the energy transfers involved in generating electricity using:

wind water geothermal resources solar heating systems solar cells fossil fuels nuclear power

4.17 describe the advantages and disadvantages of methods of large scale electricity production from various renewable and non-renewable resources.

b) Energy transfer4.2 describe energy transfers involving the following forms of energy: Thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Gravitational Potential, Elastic Potential, Nuclear Potential and Chemical Potential are types of stored energy as the energy ‘waits’ to be released. These are often at the start or end of a chain of energy transfers.

4.3 understand that energy is conserved

4.4 know and use the relationship:

Efficiency = Useful energy outputTotal energy output

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams

a) Potassium Manganite using curved apparatus (Liquids)

DiagramMethod:

4.6 describe how energy transfer may take place by conduction, convection and radiation4.7 explain the role of convection in everyday phenomena

4.8 explain how insulation is used to reduce energy transfers from buildings and the human body.

Convection of air in a room:

When air particles heat up, they move apart. The bottom part of the room of hot air is less dense than the top part of the room. So the hot air rises and creates a circulation, which is convection.

Cycling to the sea in the morning:

Lee is tired after cycling to the sea in the morning due to convection current. The sun heats up the ground quickly while the sea absorbs and preserves a lot of thermal energy. The hot air from the ground rises, which brings the cold air from the sea to move towards the land. This means Lee is riding against the wind in the morning.

Cycling back home in the evening:

Example question

Calculate the work done by a person of

mass 80kg who climbs up a set of stairs

consisting of 25 steps each of height 10cm.

W = F x d the person must exert an upward force equal their weight

the person’s weight = (80kg x 10N/kg) = 800N

the distance moved

When Lee cycles home in the evening, he will have a difficult ride home. Since the sun is gone, the ground will cool down quickly while the sea still contains hot air. So hot air will rise from the sea and the wind will blow towards the sea, against Lee.

Tectonic Plates Cloud formation

Freezer Boiling water

Work and power4.9 know and use the relationship between work, force and distance moved in the direction of the force:

work done (J) = force (N) × distance moved (m)W = F × d

Work done is how much energy is transferred from one form to another.

movement against an opposing force

Example question

Calculate the work done by a person of

mass 80kg who climbs up a set of stairs

consisting of 25 steps each of height 10cm.

W = F x d the person must exert an upward force equal their weight

the person’s weight = (80kg x 10N/kg) = 800N

the distance moved

Example

Calculate the gravitational potential energy gained by a student of mass 70kg climbing a flight of stairs of height 4m. GPE = m x g x h= 70kg x 10N/kg x 4m

GPE = 2 800 J

4.10 understand that work done is equal to energy transferred the amount of work done is equal to the energy transferred from one form to

another

980 joules of chemical energy from food eaten by the weight lifter was transferred to 980 joules of gravitational potential

energy to the barbell.

4.11 know and use the relationship:

gravitational potential energy = mass × g × heightGPE = m × g × h

energy an object possesses due to its height from the Earth’s surface. the higher an object is moved from the Earth’s surface the more potential

energy it will possess Like kinetic energy gravitational potential energy also depends on the mass of

the object work is done on the object against the force of gravity

Elastic Potential Energy the energy stored in a

material when it is stretched

4.12 know and use the relationship:

kinetic energy = 12 × mass × speed2

KE= 12 mv2

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

Conservation of Energy & Energy Transfer

Worked examples

Galileo drops a 100g stone from the leaning tower of pisa, which is 45m high.

A) How much potential energy does the stone have at the top?

GPE = mgh

GPE = 0.1kg x 10N/kg x 45m

GPE= 45J

B) What is the potential energy transferred into as it falls?

Kinetic energy

C) If the energy is conserved. How much K.E. would the stone have just before it hits the

ground?

45J since all the GPE has transferred into KE – conservation of energy

D) If the stone has 45J of kinetic energy, what speed would it hit the ground at?

We need to rearrange the kinetic energy equation: KE= 12 mv2

V=√2KEm

E) Equate the GPE equation and the KE equation.

ExampleA bullet is fired straight into the air at a speed of 300m/s. The mass of the bullet is 50g. Howhigh will the bullet travel? Would a 200g bullet travel higher, lower or to the same height?

AnswerA bullet is fired straight into the air at a speed of 300m/s. The mass of the bullet is 50g. Howhigh will the bullet travel? Would a 200g bullet travel higher, lower or to the same

height?

Example:

A 1 tonne car (1000kg) travels at 20m/s. Its brakes can apply a force of 2.8kN. What is the braking distance?

Answer: