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Marsiling Secondary School Secondary 1 Express Science Measurement: Physical Quantities, S.I. Units & Prefixes Name: ___________________ (

) Class: ________

Date: ____________

Internet Research: Three interesting facts about units… 1. ___________________________________________________________________ 2. ___________________________________________________________________ 3. ___________________________________________________________________

SI Units : International System of Units The five most commonly used base units: Physical quantity

I think the SI unit is…

Actual SI unit

Symbol

Length

Metre

m

Mass

Gram

g

Time

Second

s

Temperature

Kelvin

K

Electric current

Ampere

A

Activity: Arranging quantities from shortest to longest. Consider and arrange these items according to their lengths : Door, window, ant, distance to Kuala Lumpur, bacteria, hair Quantity Object

Length

Prefix

With Prefix

Bacteria

0.000005 m

micro(µ)

5 µm

Ant

0.003 m

milli(m)

3 mm

Hair

0.14 m

centi(c)

14 cm

Window

0.8 m

-

-

Door

2.1 m

-

-

Distance to Kuala Lumpur

315 000 m

-1-

kilo(k)

315 km


Prefix  Prefixes represent very large and very small quantities The table shows the meaning and examples of different prefixes. (** Important)

Prefix

Symbol

Meaning

Number

Example

tera

T

One trillion

1 000 000 000 000

Terametre (TM)

giga

G

One billion

1 000 000 000

Gigabyte (GB)

**mega

M

One million

1 000 000

Megawatt (MW)

**kilo

k

One thousand

1 000

Kilogram (kg)

hecto

h

One hundred

100

Hectometre (hm)

deca

da

One ten

10

Decagram (dag)

Prefix

Symbol

Meaning

**deci

d

OneTenth

**centi

c

**milli

Number

Example

1 = 0.1 10

Decimetre (dm)

One hundredth

1 = 0.01 100

Centimetre (cm)

m

One thousandth

1 = 0.001 1000

Millimetre (mm)

**micro

Âľ

One millionth

1 = 0.000001 1000000

Micrometre (Âľm)

nano

n

One billionth

1 1000000000

Nanometre (nm)

pico

p

One trillionth

1 1000000000000

Picometre (pm)

Conversion of units. Recall: 1 km

=

1 000 m

1m

=

1 00 cm

1 cm

=

1 0 mm

1 kg

=

1 000 g

1l

=

1 000 ml

,

e.g. 2.5 km

=

1 000 cm3

2

=

2500

m


Converting units in length:

km ÷1000

×1000

m ×100

÷100

cm x10

÷10

mm

Converting units in mass:

kg ×1000

÷1000

g ×100

÷100

cg x10

÷10

mg Convert metre to millimetre: Step by step method Convert to centimetre first then to millimetre, 1m

=

1x

100

=

1 000 mm

x

10 mm

Prefix method ‘milli’ means 1 thousandth, 1 mm =

0.001 m

1m

1 000 mm

=

Similarly, convert gram to milligram: 1g=

1 000 mg

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Examples:

Convert the following length/mass to the given unit. (a)

3.4 km

= 3.4 x 1000 m = 3400 m

(b)

1.8 mm

= 1.8 ÷ 10 = 0.18 cm

(c)

0.7 cm

= 0.7 ÷ 100 = 0.007 m

(d)

38 g

= 38 x 1000 = 38000 mg

Practice (a)

42.19 km

= _____________________42190 m

(b)

0.67 g

= ________________________670 mg

(c)

154 cm

= ________________________1.54 m

(d)

2.5 mm

= ________________________0.25 cm

Test yourself ! (Homework) 1)

140 Length of a table = 1.4 m = ____________ cm

2)

45 Mass of a person = 45 000 g = ____________ kg

3)

2 500 Electric power of a water heater = 2.5 kW = ____________ W

4)

300 000 000 Speed of light = 300 000 km per sec = _________________ m per sec

5)

0.24 Height of a water bottle = 24 cm = ____________ m

6)

1.2 Thickness of a plastic ruler = 0.0012 m = ____________mm

7)

0.25 Mass of a small medicine tablet = 250 mg = _____________ g

8)

Thickness of a red blood cell = 8 µm = _____________ m

9)

Size of a computer file = 7.86 MB = ___________________ B

10)

Given that 1 m2 = 10 000 cm2 ,

96 500 9.65 m2 = ___________ cm2.

11)

Given that 1 m3 = 1 000 000 cm3 ,

11 500 000 11.5 m3 = ______________ cm3

0.000 008

7 860 000

4


Reflections: metre(m) _______, gram(g)  The 5 common SI units are ________, second(s) Ampere(A) _______, Kelvin(K) _________ and _________.

 Prefixes are added to a physical quantity to make it understand easier to ________________. meanings  Different prefixes have different _______________ symbols and _______________.

 There are 6 most commonly used prefixes, they are : Mega  _____________ (M) Kilo  _____________ ( k) Deci  _____________ (d) Centi  _____________ ( c ) Milli  _____________ ( m ) Micro  _____________ ( Âľ )

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Measurement