physipics

TWO:

ENERGY

NOTE: These Talk-About Frames are samples of a much larger, and growing, collection. Scroll down to see the current list.

thermal energy transfers I

Frame EN1

EN1: Thermal energy transfers I

Syllabus / specification points:

• The Sun acts as a huge store of energy, emitting energy to space

The Earth has a lower temperature than the Sun, and gains energy from it

• Energy transfers from a mug of hot energy to the cooler surroundings, by thermal processes – conduction, convection and radiation

• Loss of energy by a body can cause cooling

• Energy can become thinly spread in the large surroundings; we say it is dissipated

• Objects or systems can store, gain and lose energy; energy can transfer between them

thermal energy transfers II

Frame EN2

EN2: Thermal energy transfers II

Syllabus / specification points:

• Energy natural transfers from objects or systems at higher temperature to ones at lower temperature

• Our bodies are usually at higher temperature than our surroundings, so we lose energy and we must replace it by ‘burning’ food

• We can reduce the rate of energy loss by heating the spaces we live in, thus reducing temperature difference

• We can reduce the rate of energy loss by using layers of insulation (clothing)



Frame EN6

EN6: Work and kinetic energy

Syllabus / specification points:

• Work must be done to change motion (accelerate) and to overcome resistance to motion

• Energy is needed for doing work

• There must be a source of energy, such as fuel+oxygen; fuel may be a fossil fuel

• Moving objects have an energy store due to motion, called kinetic energy

• Energy transferred to overcome resistance becomes dissipated





how to calculate kinetic energy

Frame EN7

EN7: how to calculate kinetic energy

Syllabus / specification points:

• An object with kinetic energy has the ability to do work on other objects with which it collides, and so it is a store of energy

• The quantity of stored energy depends on the mass of the body and its speed

• Kinetic energy = 1/2 mv2





work and extra gravitational potential energy

Frame EN8

Frame EN8

EN8: Work, extra height and extra gravitational potential energy

Syllabus / specification points:

• A falling object can do work, and so acts as a store of energy

• The extra energy it has due to the potential to fall is its gravitational potential energy, GPE

• At the end of a fall, the energy may become dissipated





conservation of energy

Frame EN10

EN10: Conservation of energy

Syllabus / specification points:

• Energy cannot be destroyed

• The total energy at the end of every process is the same as at the beginning

• However, energy can become thinly spread by thermal processes, and become dissipated





conservation of energy: motion with + without resistive forces

Frame EN10.B

EN10.B: Conservation of energy during motion, with and without resistive forces

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the work done by a cyclist produces a matching increase in kinetic energy

• Where there are resistive forces work must be done to overcome them, resulting in dissipation of energy

• When resistive force is the same size as the driving force all of the work done by the cyclist results in dissipation and there is no gain in kinetic energy





conservation of energy: motion without resistive forces

Frame EN10.C

EN10.C: Conservation of energy: falling without resistive forces

Syllabus / specification points:

• The Moon has less mass than the Earth, so has smaller gravitational field strength, g

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the gravitational potential energy at the start of a fall matches the kinetic energy at the end




conservation of energy: motion with + without resistive forces

Frame EN10.D

EN10.D: Conservation of energy: falling with and without air resistance

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the gravitational potential energy at the start of a fall matches the kinetic energy at the end

• However if there is air resistance then there is some heating and air movement caused by the fall; then some energy is dissipated and kinetic energy at the end of the fall is less than the gravitational potential energy at the start






conservation of energy: motion without resistive forces

Frame EN10.E

EN10.E: Conservation of energy: motion without resistive force

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the gravitational potential energy at the highest point matches the kinetic energy at the lowest point

• A pendulum, such as a playground swing, loses and gains gravitational potential energy and kinetic energy, in turn

• When there are is no need for work to be done to overcome resistive forces then there is no dissipation






conservation of energy: motion with resistive forces

Frame EN10.F

EN10.F: Conservation of energy: motion with resistive force

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are resistive forces the gravitational potential energy at the highest point matches the total of dissipated energy plus kinetic energy at the lowest point

• There is loss of energy, by dissipation, during every swing, so the maximum gravitational potential energy and the maximum kinetic energy gradually become smaller

• A source of energy is needed to compensate for the dissipated energy






conservation of energy: motion with resistive forces

Frame EN10.G

EN10.G: Conservation of energy: changes of GPE and KE during orbit in space

Syllabus / specification points:

• The physics that applies to playground swings also applies to large objects in space

• Pluto is sometimes closer to the Sun and sometimes further away

• It has kinetic energy (due to its motion) and gravitational potential energy (due to the Sun’s gravitational field)

• When it is closest to the Sun it’s gravitational potential energy is minimum, so kinetic energy is maximum

• When it is furthest from the Sun it’s gravitational potential energy is maximum, so kinetic energy is minimum






work and kinetic energy

Energy, provisional list, May 2021


Comp: completed and ready, but so far unpublished


E1         Thermal energy transfers I                                                           FREE

E2         Thermal energy transfers II                                                          FREE

E3         Thermal energy transfers III                                                         Comp

E4         Processes of thermal energy transfer                                         Comp

E4.B     Rates of emission of radiation                                                     Planned

E5         Work: mechanical energy transfer                                               Comp

E6         Work and kinetic energy                                                              FREE

E7         How to calculate kinetic energy                                                  FREE

E8         Work and extra gravitational potential energy                             FREE

E9         Calculating extra gravitational potential energy                          Comp

E10        Conservation of energy                                                              FREE

E10.B    Conservation of energy: motion with/without resistive force      FREE

E10.C    Conservation of energy: falling without resistive force               FREE

E10.D    Conservation of energy: falling with/without resistive force       FREE

E10.E    Conservation of energy: motion without resistive force              FREE

E10.F    Conservation of energy: motion with resistive force                   FREE

E10.G    Conservation of energy: changes of KE + GPE during orbit      FREE

E11        Energy stores                                                                             Comp

E11.B     Energy storage by stretched springs and wires                        Planned

E11.C     More energy transfers: in chemical changes                            Planned

E11.D     More energy transfers: by waves                                              Planned

E11.E     More energy transfers: in electric circuits                                  Planned

E11.F     More energy transfers: in nuclear changes                                Planned

E12        Heating water I                                                                           Comp

E13        Heating water II                                                                          Comp

E14        The snowman is melting                                                            Planned

E15        Boiling dry                                                                                  Planned

E16        Power I                                                                                       Comp

E17        Power II                                                                                      Comp

E18        Thermal conductors and thermal insulators                              Comp

E17        Reducing energy loss through a wall                                         Comp

E20        Efficiency I                                                                                  Comp

E21        Efficiency II                                                                                 Comp

E22        Efficiency III                                                                                Comp

E23        Reducing dissipation due to friction                                          Comp

E24        Coal is old                                                                                  Planned

E25        Biofuels                                                                                      Planned

E26        Water flow                                                                                  Planned

E27        Water waves                                                                              Planned

E28        Underground I                                                                            Planned

E29        Underground II                                                                           Planned 

E30        Wind turbines                                                                             Planned

E31        Solar panels                                                                               Planned

E32        Solar cells                                                                                  Planned  

E33        The nuclear power industry I                                                     Planned

E34        The nuclear power industry II                                                    Planned

E35        Clean energy?                                                                            Planned







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Copyright (c) David Brodie, 2019-2021

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