Activities of Science
SI Units and Conversions p.5-6
Various standard units are used in SI to express different quantities. Prefixes can
be attached to the SI units in order to derive other SI units that are equal to the
basic unit multiplied by a power of 10.
1. Write the SI prefix for each of the following factors. (Heb p.18)
For example, 10-2 corresponds to the prefix centi.
a) 10-12 = pico
b) 0.001 = milli
c) 1 000 000 = mega
9
d) 0.1 = deci
e) 10
=
giga f) 1 000 =
kilo
g) 0.01 = centi
h) 10-15 =
femto
i) 10-9 = nano
j) 0.000 001 =micro
k) 101 = deca
l) 0.000 000 001 = nano
2. List the basic SI unit and abbreviation for each of the following
quantities:
Quantity
SI Unit
Abbreviation
length
metre
m, cm, mm
mass
kilogram, gram
kg, g
volume
litre, millitre
L, mL
2
area
metre square
m
centimetre square
cm2
3
density
gram/ cubic centrimetre
g/cm
gram/millitre
g/mL
time
second
s
Converting Units
Add 0.735 m to 4.1 cm.
Solution
i)We need every values expressed in the same unit, let’s say in cm
ii) convert the unit
0.735 m = ? cm
= 73.5 cm
larger unit: m > cm
1 large = lots small
conversion factor: 1 m = 100 cm
0.735 m X 100 cm = 73.5 cm
1m
Now add the numbers :
73.5 cm
+
4.1 cm
77.6 cm
Exercises on Converting Units
1) Convert 0.000 830 m to µm.
Larger unit: m
1 large = lots small
lign up decimal places
1 m = 1000 000 µm  conversion factor
0.000 830 m X 1 000 000 µm = 830 µm
1m
2) Convert 7.56 kg to g
Larger unit: kg
1 large = lots small
1 kg = 1 000 g
 conversion factor
7.56 kg X 1000 g = 7 560 g = 7.56 X 103g
1
1 kg
3) Convert 4.02 hours to seconds
Conversion factors:
1 large = lots small
1 min = 60 sec
1 hr = 60 min
1 hr = 3600 s
4.02 hr X 60 min X 60 sec = 14 472 sec
1
hr
min
** 4) Convert 217 m/s to cm/s.
Larger unit: m > cm
1 large = lots small
1m
= 100 cm
 conversion factor
217 m X 100 cm = 21 700 cm = 2.17 X 104 cm/s
s
m
s
5) Add 9.78 m to 345 cm. Express your answer in centimeters.
Larger unit: m > cm
1 large = lots small
1m
= 100 cm
 conversion factor
9.78 m X 100 cm = 978 cm
1 m
978 cm + 345 cm = 1323 cm
6) Multiply 52 mm by 1.0 cm.
Larger unit: cm > mm
1 large = lots small
1 cm = 10 mm
 conversion factor
1.0 cm X 10 mm = 10 mm
1 cm
52 mm X 10 mm = 520 mm2
or
5.2 cm X 1.0 cm = 5.2 cm2
7) Multiply 31 cm/s by 5 min.
We have to convert min into seconds
5 min X 60 sec = 300 sec
min
31 cm X 300 sec = 9 300 cm
sec
Practice Problems
*T* 1) Express 1123 pg in nanograms
Larger unit: ng > pg
1 large = lots small
1 ng = 1 000 pg
1123 pg X 1 ng = 1.123 ng
1
10 3 pg
2) Express 2.5 mm in micrometers.
Larger unit: mm
1 large = lots small
1 mm = 103 µm
 conversion factor
2.5 mm X 103 µm = 2.5 X 103 µm = 2500 µm
1
1 mm