SCIENCE FORM 1 CHAPTER 1 (1.3 : PHYSICAL QUANTITIES & THEIR UNITS)

1 PCehnagpetneral1a:nInkterpoadduacPtieonnyitaosSactaiennStiafinctIinfivkestigation

Scientific Methodology

Do you realise that our life is based
on science? This includes the food we
eat, the clothes we wear, our modes of
transportation and the energy we use.

Chapter 1 1

PCehnagpentearla1n: IknetproadaucPteionnyitaosaStcainenStaifiinctiIfnikvestigation

1.3 Physical Quantities and Their Units

Let’s learn

• Identify and use the correct units for different physical quantities.
• Identify the symbols and values of prefixes used in measurement.
• Convert base quantity units for mass, length and time such as grams to kilograms, centimetres to

metres, seconds to hours and vice versa.
• Justify the importance of the use of S.I. units in daily life.

Recall the measurements that you Table 1.2 Base quantities
have learned in primary school.
A physical quantity in science is Base quantity S.I. unit Symbol of S.I. unit
defined as a physical characteristic Length metre m
that can be measured. The common Mass kg
base quantities used are length, Time kilogram s
mass, time, temperature and electric Temperature second K
current (Table 1.2). Electric current kelvin A
ampere

The International System of Units, known as S.I. units S.I. units have been used
(Système Internationale d’Unités) is used for the consistency as the standard unit of
of measurement. This allows accurate exchange of data and physical quantities since
scientific knowledge to the entire world. 1960 to prevent problems
of inconsistent units in
1.5 measurement.

Aim: To identify physical quantities, values and S.I. units

Instruction
1. Look at the objects in Photograph 1.10. State the S.I. unit that you can use to measure

the physical quantity of each object.
(a) (b) (c)

Length of table Mass of onion Temperature of water

Photograph 1.10 Objects
2. Observe the values and units that are used on the specification and labels of daily

products.
3. Record your observation in your practical book.

Value and unit Value and unit
Photograph 1.11 Daily products Chapter 1 15

Prefixes can be used if the value of a physical quantity unit is too big or too small.
Table 1.3 The values of prefixes and symbols for physical quantity units

Prefix Value Standard form Symbol Prefix values are important
giga 1 000 000 000 109 G and are used widely in
mega 106 M calculations.
kilo 1 000 000 103 k
deci 1 000 10–1 d
centi 0.1 10–2 c
milli 0.01 10–3 m
micro 0.001 10–6 µ
nano 10–9 n
0.000 001
0.000 000 001

Converting Units of Base Quantity

a Mass

× 1000 Example:

1. 1.9 kg = g

1.9 kg = 1.9 × 1000

kilogram (kg) gram (g) = 1900 g

2. 8200 g = kg

8200 g = 8200 ÷ 1000

÷ 1000 = 8.2 kg
× 1000
b Length × 10 × 10 × 10

kilometre (km) metre (m) decimetre (dm) centimetre (cm) millimetre (mm)

÷ 1000 ÷ 10 ÷ 10 ÷ 10

Example: Example: Example:
1. 80 m =
80 m = 80 × 100 cm 2. 600 cm = m 3. 95 mm = m
= 8 000 cm
600 cm = 600 ÷ 100 95 mm = 95 ÷ 1000

= 6 m = 0.095 m

c Time × 60 Example: Example:
1. 7 min =
× 60 7 min = 7 × 60
= 420 s
hour (hr) minutes (min) second (s) s 2. 450 s = hr

450 s = 450 ÷ 60 ÷ 60

÷ 60 ÷ 60 = 0.125 hr
16 CBhaabp1ter 1

PCehnagpentearla1n: IknetproadaucPteionnyitaosaStcainenStaifiinctiIfnikvestigation

The Importance of S.I. units in Life

Inconsistencies of units used in daily Recall the measurements that you have learned in primary
life may cause a lot of problems. For school such as span, fathom, pace and cubit.
example, people in certain places may
measure things by using pound and (a) Span (b) Fathom
ounce, whereas people in other places
may use grain and stone. The use of a (c) Pace (d) Cubit
standard unit for measurement will
make it easier for scientists to
communicate at international level.
Problems shown in the situations below
may arise if we do not use standard
units.

Figure 1.8 Measurements in olden times

Situation 1 Situation 2

Zaidi and Hafiz, please Syura, please go Okay,
measure the length of the and buy three mother.
fathoms length
classroom by counting of cloth for the
your paces. curtain.
Okay, teacher.

Uncle, I want to buy
three fathoms of cloth

to make a curtain.

40 paces 51 paces

Teacher, why They are different Mother, why Syura, your
do we have because the length is the cloth fathom is
different number of your paces are shorter because
of paces? so long? you are still a
different.
child.

ChapBtaebr 1 17

1.6 21 ICS

Aim: To understand the implication of non-standardised units in our life
Instruction
1. Work in groups.
2. Each group should gather information on the implication of non-standardised units

in life.
3. Each group will present their discussion in class by using multimedia presentation such

as PowerPoint.

1.3

1. List five physical quantities that you have studied. What is the S.I. unit and the symbol used
for each of the quantities?
2. Convert the values below.
(a) 0.13 m = cm (d) 24 000 g = kg
(b) 18 000 mg = kg (e) 0.006 A = mA
(c) 4 m = µm

The Use of Measuring Instruments,
Accuracy, Consistency, Sensitivity
1.4 and Errors

Let’s learn

• Use the right measuring instrument and use it the right way to measure accurately and consistently
the quantities of length, mass, time, temperature and electric current.

• Use measuring instruments with higher accuracy and compare the measurements in terms of
accuracy, consistency and sensitivity.

• Explain how to minimise systematic errors and random errors.
• Estimate the length, area, mass or volume of an object before taking actual measurements.
• Explain with examples innovations of various types of measuring instruments through a multimedia

presentation.

F or the purpose of measurement, different measuring Accuracy – The ability of
measuring instruments to
instruments are needed to collect data in an experiment. obtain a value closest to the
We need to ensure that we use the right measuring actual value.
instruments to measure the quantities of length, mass, time, Consistency– The ability of
temperature and electric current accurately and consistently. measuring instruments to
give the same readings with
Photograph 1.12 Measuring instruments repeated measurements.
18 Chapter 1 Sensitivity – The ability of
measuring instruments to
detect a small change in the
measurement quantity.