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Thermal energy: 1.1 What is a thermal energy store? Introduction to thermal energy and kinetic energy particle model of the three states of matter.

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INDEX for physics notes on thermal energy transfer by conduction, convection and radiation

 1.1 Introduction to thermal energy ('heat energy') transfer

  • Thermal energy is the energy contained in a system of particles due to their kinetic energy of vibration or movement from place to place.

    • It is better to use the phrase 'thermal energy', rather than the phrase 'heat energy'.

  • Energy can be transferred from one place to another by work or by heating processes.

  • You  need to know and understand how this energy is transferred and which heating processes are most important in a particular situation.

  •  When energy is transferred to an object by some means or other, the energy is stored in the object's energy store.

  • This energy store may be thermal (dealt with here), chemical, kinetic, magnetic, gravitational potential, elastic potential or nuclear.

  • Here we are interested in energy transfer by heating (conduction, convection) and infrared (radiation).

  • Heat energy must always flow from hotter material at a higher temperature to cooler material at a lower temperature and the bigger the temperature difference the bigger the rate of heat energy transfer.

  • eg the greater the temperature difference between a body and its surroundings like a hot object like a mug of coffee standing in a cold room, the faster the heat energy is transferred from the hotter material to the cooler material (eg surrounding air).

  • Systems, thermal energy stores and states of matter

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  • System is a word that means a particular object or objects that is being looked at in a particular context eg boiling water in a kettle.

  • When a system changes, energy is transferred into or out of the system, this may be between different objects/materials in the system or perhaps between different energy stores (same of different).

  • Closed systems are systems that do not allow energy to leave or enter (lose or gain) so the ne change in the total energy is zero.

  • When an object/material is heated to raise its temperature, the thermal energy store of the object is increased.

    • This thermal energy is stored throughout all the material by increasing the kinetic energy (KE) stores of the material's individual particles eg the KE particle vibration in a solid and the KE of the rapid movement of the freely moving particles in a liquid or gas.

    • The thermal KE is distributed by either the particles vibrating against each other in a solid or the collisions between the freely moving particles in a gas or liquid. Higher KE particles will on average lose energy to lower KE particles - that's the way energy 'flows'.

    • The higher the temperature of particles the greater their average kinetic energy so they will vibrate more violently in a solid and move faster in gases and liquids.

    • Once heat energy has stopped being supplied to an object, it will distribute itself evenly to give a uniform temperature throughout the material by conduction or convection. However, if object's/material's surroundings are at a lower temperature, then heat energy will drain from this thermal store until its temperature has fallen to that of the surroundings - that's the way heat flows!

    • -

  • The amount of thermal energy transferred can be calculated from the formula

    • energy transferred (J) = mass (kg) x specific heat capacity (J/kgoC) x temperature change (oC)

    • For more details of calculations see  

See also

Specific heat capacity: How to determine it, use of data, calculations and thermal energy stores

Particle theory models, internal energy, heat transfer in state changes, latent heat, particle motion

Notes on thermal energy transfer by conduction, convection, radiation

Keywords, phrases and learning objectives for a thermal energy store and particle models

Know what me mean by a thermal energy store.

Be able to explain that a thermal energy store can be described using a kinetic energy particle model of the three states of matter - gas, liquid or solid.

  • Check out your practical work you did with thermal energy you did or teacher demonstrations you observed in all of this is part of good revision for your module examination context questions and helps with 'how science works'.

    • Passing white light through a prism and detecting the infrared radiation with a thermometer.

    • Demonstration using balls in a tray to show the behaviour of particles in substances in different states i.e. gas, liquid and solid.

    • Measuring the cooling effect produced by evaporation by putting wet cotton wool over the bulb of a thermometer or temperature probe.

    • Plan and carry out an investigation into factors that affect the rate of cooling of a can of water, eg shape, volume, and colour of can using Leslie’s cube to demonstrate the effect on radiation of altering the nature of the surface.

    • Investigating thermal conduction using rods of different materials.


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Notes on thermal energy transfer by conduction, convection, radiation