Chapter No. 1

Physical Quantities:

                        All the measurable quantities are called physical quantities.

                Physical quantities are divided in to two parts “Base quantities and Drive Quantities.”

                Base Quantities:

                            Base quantities are the quantities on the basis of which other quantities are expressed. There are seven base quantities. These are mass, length, time, electric current, temperature, intensity of light and amount of substance.

            Derived Quantities:

                                The quantities that are expressed in terms of base quantities are called derived quantities. These are area, volume, speed, force, torque, power, work, energy, charge etc.

International System of Units:

                            The eleventh General conference on weight and measures held in Paris in 1960 adopted a world-wide system of measurement called International System of Units.

                                Base Units:       

                                                The units that describe the base quantities are called base units.

Base quantities, their SI units with Quantity

Quantity		Unit
Name	Symbol	Name	Symbol
Length	l	Meter	m
Mass	m	Kilogram	kg
Time	t	Second	s
Electric Current	I	Ampere	A
Intensity of light	L	Candela	Cd
Temperature	T	Kelvin	K
Amount of a Substance	n	Mole	mol

Derived Units:

                                                                The unit used to measure derived quantities is called derived units.

Derived quantities, their SI units with Quantity

Quantity		Unit
Name	Symbol	Name	Symbol
Speed	v	Meter per second	ms-1
Acceleration	a	Meter per second per second	ms-2
Volume	V	Cubic meter	m3
Force	F	Newton	N
Pressure	P	Pascal	pa

Prefixes:

SI units have the advantage that their multiples and sub-multiples can be expressed in terms of prefixes. Prefixes are the words or letters added before SI units such as kilo, mega, giga, and milli etc.

i.e.

Divide 20,000g by 1000 to express it into kilogramme, since kilo represents 10³ or 1000. Thus                              kg          =             20kg       or            20000g  =             20×10³g                = 20kg

Some Prefixes

Prefix	Symbol	Multiplier	Prefix	Symbol	Multiplier
exa	E	1018	deci	d	10-1
pera	P	1015	centi	c	10-2
tera	T	1012	milli	m	10-3
giga	G	109	micro	u	10-6
mega	M	106	nano	n	10-9
kilo	K	103	pico	p	10-12
hecto	h	102	femto	f	10-15
deca	da	101	atto	a	10-18

Scientific Notation:

                                A simple but scientific way to write large or small numbers is to express them in some power of ten.
Read More ...