1.2 Base Quantities and Derived

Understanding physics

What is physics?

• “Physikos” – knowledge of nature• Physics

- to find answer to the question ‘why’ and ‘how’ in relation to the mysteries the universe

- to explain the fundamental nature of the universe by using simplest explanation

- to gain a better understanding of the world

- the law of physics : help us to answer question

Prepared by:

Physics Department

SBPI Temerloh

2006

Understanding base quantities and derived quantities

• Measurement is the process of determining the value of quantity using a scientific instrument with a standard scale

• Physical quantity

- A quantity that is measurable

- Eg: room temperature, the pressure of a gas• Non-physical quantities

- Quantities that cannot be measured

- Eg:…….?

• Physical quantities are categorized:

(i) base quantities

(ii) derived quantities

BASE QUANTITIES

• Are physical quantities that cannot be defined in terms of other physical quantities

Base quantities Symbol SI unit SI unit Symbol

Length l metre m

Mass m kilogram kg

Time t seconds s

Temperature T kelvin K

Electric current I Ampere A

DERIVED QUANTITIES• Are physical quantities derived from base quantities by

multiplication or division or both.

Derived quantities

Symbol Formula Unit

Area A Length x length m2

Volume V Length x length x length m3

Velocity v m s-1

Density ρ kg m-3

time

length

volume

mass

Example:A 3.5 kg of chicken, cut into pieces of about 8 cm long. Add 5 g of salt and 15 cm3 of ginger juice. Season for 25 minutes. Deep fry until the chicken pieces turn brownish colour. Place it in a 100 cm2 plate and let it cool down to 80 0C before serve. From the recipe provided above, identify the physical quantities and then classify them into base quantities and derived quantities.

SOLUTION:

Mass – 3.5 kg chicken, 5g saltLength - 8 cm longVolume - 15 cm3 of ginger juiceTime - 25 minutes. Area - 100 cm2 plate Temperature - 80 0C

Base quantities

Derive quantities

Mass

Length

Time

Temperature

Volume

Area

STANDARD FORM

• To express very larger or very small number – to be neater, brief and easier to read

• The standard form written as;

n is an integer (+ve and –ve)

• Eg: Speed of light = 300 000 000 m s-1

= 3.0 X 108 m s-1

• Eg; wavelength of yellow light = 0.000 000 58 m = 5.8 X 10-7m

n10A101 A

PREFIXES

• A prefix is the pre-multiplicative factor which is used in a measurement when its value is very large or very small on the SI unit scale

• Measurement whose magnitude is very large- kilo, Mega, Giga and Tera

• Measurement whose magnitude is very small – centi, mili, micro, nano, pico

Prefix Symbol Power/

factor

Value

Tera

Giga

Mega

Kilo

deci

centi

milli

micro

nano

piko

T

G

M

k

d

c

m

μ

n

p

1012

109

106

103

10-1

10-2

10-3

10-6

10-9

10-12

1 000 000 000 000

1 000 000 000

1 000 000

1 000

0.1

0.01

0.001

0.000 001

0.000 000 001

0.000 000 000 001

You have to memories

this table….NO

W

Conversion of units

PREFIX BASE

x

÷

PREFIX PREFIX

÷

Examples:1. Convert the following masses to kilogram and giving the answer

in scientific notation

(a) 0.041 Mg

(b) 512 000 000 g

Solution :

(a) 0.041 Mg…….kg (prefix to prefix)

= 0.041 X 106 ÷ 103 kg

= 0.041 X 106 - 3 kg

= 4.1 x 10-2 x 103 kg

= 4.1 x 101kg

Solution :

(b) 512 000 000 g…….kg (base to prefix)

= 512 000 000 ÷ 103 kg

= 5.12 x 108 x 10-3 kg

= 5.12 x 105 kg

What are you waiting for? Try to answer next

question

Example 2• Convert every measurement to base unit

(a) 2.15 x 108nm

(b) 2.15 x 10-2 cm

Solution:

(a) 2.15 x 108nm…..m (Prefix to base)

= 2.15 x 108 x 10-9m

= 2.15 x 10(8+ -9) m

= 2.15 x 10-1 m

Solution:

(b) 2.15 x 10-2cm…..m (Prefix to base)

= 2.15 x 10-2 x 10-2m

= 2.15 x 10(-2+ -2) m

= 2.15 x 10-4 m

Now lets try to answer next exercise…..

Exercise to be answer….• Express each measurement in column I in the unit

specified in column II. Show the solution.

I II

(i) 0.4 mm

(ii) 10 g

(iii) 240 mg

(iv) 0.02 kg

(v) 3.86 ms

(vi) 3.86 Ms

(vii) 6.37 Gm

(viii) 6.37 km

m

kg

kg

g

ns

ds

m

μm

I II

(ix) 40 cm2

(x) 4.2 mm2

(xi) 1.05 g cm-3

m2

m2

kg m-3

THE END