Page 51 - 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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36 Automobile mechanical and electrical systems

1.4 Basic science, materials, mathematics and
mechanics

1.4.1 Introduction

When you want to work on motor vehicles, it is easy to wonder why you should
Key fact
study maths, science, materials, electricity and other similar subjects. The
Understanding basic principles answer is that understanding basic principles will mean that you will be a better
will mean that you will be a better technician because you know how things really work – and you will have the
technician.
skills to fi gure out how something you have not seen before works.
Often the words used to describe scientifi c principles can be confusing. Table 1.16
picks out the most important terminology and a simple explanation is given. Some
of the terms are described in more detail in later sections.

Table 1.16 Useful terminology
SI units A set of standard units so we all talk the same language. SI stands for ‘Système International’. This is
French for ‘International System’!
Ratio The amount of one thing compared to another, e.g. two to one is written as 2:1
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Area (m ) Amount of surface of anything, e.g. the surface area of a car roof would help you know how much paint
would be needed to cover it
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Volume (m ) Capacity of an object, e.g. 1000 cc (cubic centimetres) or one litre of paint to do the job above
Mass (kg) The quantity of matter in a body. Volume does not matter, e.g. which has the greater mass, a kilogram of
lead or a kilogram of feathers? They both have the same mass, but have different volumes
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Density (kg/m ) A full paint tin has a greater mass than an empty tin, but the volumes are the same

Energy (J) The ability to do work or the amount of work stored in something; e.g. petrol contains a lot of energy in
chemical form

Force (N) When you push an object it moves (if you can apply enough force)
Work (J) Work is done when the force applied to an object makes it move. Work can also be said to be done
when energy is converted from one form to another
Power (W) The rate at which work can be done, e.g. energy used per second

Torque (Nm) A turning force like a spanner turning a nut. A longer spanner needs less force
Velocity (m/s) A scientifi c name for speed; e.g. the UK national velocity limit is 70 mph (not an SI unit!)
Acceleration The rate at which velocity changes. If positive then the car, for example, will increase in speed. If negative
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(m/s ) (or deceleration) such as when braking, the car’s speed decreases
Momentum The combination of the mass of a body and its velocity. A large goods vehicle has much greater momentum
(kg m/s) than a car at the same speed. It must have much better brakes or it will take a lot longer to stop
Friction (μ) When one surface moves over another friction tries to stop the movement. It is interesting to note that
without friction a moving object such as a car would not stop!
Heat (J) This is a measure of the amount of energy in a body. Heat can only transfer from a higher to a lower
temperature and this will be by conduction, convection or radiation
Temperature (°C) A measure of how hot something is, but this must not be confused with the amount of heat energy
(Continued)