Chapter 8 Heat:
Is heat a form of Energy?:
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Heat is a form of energy as it has the ability to do work. For example, it can force a hot air balloon to rise
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It can also be concealed into other forms of energy for example, in a filament bulb heat is converted into light
Expansion and Contraction:
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An effect that heat can have on an object is expansion. For example, tapered joints are used on railways to allow room for expansion
There are both advantages and disadvantages to Expansion:
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Advantage: Some metals expand more than others and we can use this to our advantage. For example, we use a bimetallic strip (two metals joined together). When heated these strips expand and bend which can be used to connect or close a circuit e.g light switch
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Disadvantage: Can cause telephone wires to sag in the middle and can cause 700 meter bridges to be 25 cm's longer
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Also, when cooled objects contract such as electric wires this can cause them to snap.
Hot air balloons are a key example that heat is a form energy
The diagram demonstrates the sagging of electrical wires on a cold day
Water is breaking its contract:
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Like most things liquids contract when cooled and expand when heated
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However water is unique in that it does start to contract when cooled but only up to 4 degrees celcius. This is when it starts to expand
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As you learned from the water section water is denser than ice. There are both advantages and disadvantages to this.
Advantage: Water is at its densist at 4 degrees celcius because its volume is smallest. As soon as the water at the top of the lake reaches 4 degrees celcius it sinks to the bottom of the lake while it is 0 degrees celcius at the top of the lake.
Disadvanatage: When cold weather sets in pipes can freeze, expand and burst.
Heat Transfer:
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Conduction, convection and radiation are the three main methods of heat transfer
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The main difference between these three methods is how the heat is transfered and with what
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Heat is a form of energy in which heat travels from a warm object to a cold object
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Conduction: Is the method by which heat travels from particle to particle in a solid e.g. a metal spoon. However, conduction cannot take place in an insulated solid like a wooden spoon
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An insulator is a substance which does not allow heat to flow through it easily
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Convection: Convection is the transfer of heat through a liquid or gas when the particles of the liquid/gas move up and carry the heat with them
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Radiation: Is the transfer of heat from a hot object without the need of a medium.
