Science:Heat

Science:Heat

1. Heat:Is a form of energy.It is measured in joules.

2. Energy:This is the ability to do work to move something.It is measured in Joules.

3. Solids expand (grow) when heated and contract(shrink) when cooled

   • The ball and ring experiment allows us to show that soilds expand when heated and contract when cooled.
     • The Bimetallic Strip:Used in somke alarms and thermostats.When the bimetallic strip is heated the copper expands more than the iron.This causes the bimetallic stip to bend.The Bimetallic strip will return to its original shape whe it cools.
       • • Bimeattalic strip being used in a Fire Alarm

4. Liquids expand when heated and contract when cooled.

   • This is the principal/idea on which a thermometer is based.The mercury in the thermometer will rise when heated(because it is a liquid and it expands).This shows an increase in tempreture.

5. Gases:Expand when heated and contract when cooled.

   • This is the reason you are told never to put an aerosol can on a fire,this is also the reason that air ballons fly.
     • Why Does the air balloon rise when air is heated?
       • It rises because the air inside expands allowing the balloon to "float".The air outside is colder and more dense,as a result the balloon can easily float (because the air inside is less dense than the outside air).
         • • Hot Air balloon

6. Water is u unusual because as water cools it contracts at 4'C,water starts to expand! Water freezes and forms ice at 0'C.

   • This is why water pipes burst during winter.
   • Boiling Point of Water changes with pressure: -Normal boiling point:100'C -If the atmospheric pressure is lower it will boil lower. -If the atmospheric pressure is higher the boiling point will be higher.
     • • Pressure Cooker
         • Food cooks more quickly in a pressure cooker because it is tightly sealed and this increases the pressure inside.Due to the increased pressure the boliling point of water increases.This causes the veg to cook more quickly.

7. Tempreture:Is the measure of how hot or cold an object is.It is measured in ' Celsius.

8. Latent Heat:Is the heat taken in or given out when a substance is changing state without changing tempreture

   • When Materials change state,energy is taken in(aborbed)or given out(released).
   • Solid changing to a liquid----->Latent heat is taken in by material.
   • Liquid changing to a solid------>Latent heat is given out by matireal
   • Liquid changing to a gas------>Latent heat is taken in by matireal
   • Gas changing to a liquid------>Latent heat given out by matireal
   • A burn from steam is worse than one from liquid beacsue the steam contains more latent heat (a liquid changing to a gas takes in heat.)
   • Latent Heat of Vaporisation:When heat changes a liquid to a gas.
   • Latent Heat of Fusion: When heat changes sold to a liquid
   • • Graph that shows Latent Heat

9. Heat Transfer

   • Conduction:This is the transfer of heat through a substance without any overall movement of the substance itself.Conduction is the method by which heat travels from particle to particle through a solid.
   • Convection:Heat moves through liquid and gases by convection.In convection the particles move upwards carrying the heat with them.The movement of the heated particles in liquids or gases causes convection currents.
   • Radiation:Is the transfer of heat from one object to another without the needing a medium.This is the way that heat travels from the sun to the earth.To show convection currents in water we use potassium permangnde.This allows us to see the upwards movement of particles clearly.

10. Conductors and Insulators

    • Conductors:Is a substance which allows heat to flow through it easily.E.G-Metals
      • To show conduction and which metals are better conductors
        • The Order in which the pins fell off: 1)Copper 2)Aluminium 3)Iron
    • Insulators:Is a substance which does not allow heat to flow through it easily.E.G-Wood,Gas(Trapped air),Wool.
      • Insulation in the home:
        • Double Glazed windows(air trapped between the two panes of glass)
        • Fiber glass in the attic
        • Areoboard in the cavities of walls
        • Tog Value:A high tod value means a good insulator(Tog value is involved with mattresses).
    • A good insulator is a poor conductor of heat.

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