Page 59 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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44 Automobile mechanical and electrical systems

1.4.12 Heat and temperature

Heat is a form of energy possessed by a substance by virtue of the vibrating
movement or kinetic energy of its molecules or atoms. Heat only fl ows from a
higher temperature to a lower temperature. Its effect on a substance may be
simply to raise its temperature, or to cause it to expand. Solids can melt, liquids
vaporize and gases if confi ned will increase in pressure. This is much like ice,
water, steam and steam pressure in a boiler.
Quantities of heat are usually measured in units of energy, such as joules (J). The
specifi c heat capacity of a substance is the ratio of the amount of heat energy
required to raise the temperature of a given mass of the substance through a
given range of temperature, to the heat required to raise the temperature of
an equal mass of water through the same range. This is useful for comparing
materials.
Heat energy is transferred by conduction, convection and radiation. Conduction
is the passing of heat along a medium to neighbouring parts. For example, the
whole length of a metal rod becomes hot when one end is held in the fl ame of a
welding torch. Convection is the transmission of heat through a liquid or gas in
currents, for example when the air in a car is warmed by the heater matrix and
blower. Radiation is heat transfer by infrared rays. It can pass through a vacuum
Figure 1.59 Measuring relative density and travels at the speed as light. For example, you can feel radiated heat from a
with a hydrometer vehicle headlight just in front of the glass.

Defi nition 1.4.13 Percentages

Heat
1.4.13.1 Example 1
Heat is a form of energy.
If a data book says 30% antifreeze and the cooling system holds 8 litres, how
much antifreeze should you add? ( Fig. 1.60 )
30% means 30 100,/ which cancels to 3 10/

100% when full 3 10/ 8 24 10/ 2 4litres.
1.4.13.2 Example 2
If your normal pay rate is £10 per hour, how much will you get if you are given a
22% rise?
30% to here

22% means 22 100/

22 100/ £ 10 £ 2 20.
Figure 1.60 Percentage
Your new pay rate is £10 £2.20p £12.20 per hour

1.4.14 Fractions

1.4.14.1 Example 1

If your normal pay rate is £5 per hour, how much will you get if your pay
increases by a quarter? (Fig. 1.61)

Time and a quarter means 1 1 your normal rate
4

Figure 1.61 The red block is a quarter of 1¼ £ 5 5 4/ 5 1/ 25 4/ 6 25.
the four black ones Your overtime pay rate is £6.25 per hour