Introduction To Mechanics is very important for beginners.

Physical quantity

Motion is the basic part of the mechanics. Any quantity that can be measured accurately is known as a physical quantity e.g length, mass, time, area, volume etc.

Unit

The measurement of quantities are expressed in terms of certain quantities of similar nature. This are known as units of measurement.

S.L. UNITS

Distance	Metre	m
Displacement	Metre	m
Mass	Kilogram	kg
Time	Second	s
Speed	Metres per second	Ms-1
Velocity	Metre per second	ms-1
Acceleration	Metre per second square	ms-2
Angular Velocity	Radian per second	Rad s-1

Basic  Units 

There are seven basic units

Length	metre	m
Mass	kilogram	kg
Time	second	sec
Temperature	kelvin	k
Electric current	Ampere	A
Light Intensity	candela	CD
Amount of Substance	mole	mol

ASTRONOMICAL UNIT (A.U)

The mean distance of the sun from the earth is called the astronomical unit.

I.A. U. = 1.496×10-11m

LIGHT YEAR

It is  a unit used to measure the distance between the earth and stars.

1 light year = 365 x 86400 x.3 x 10.8m

                    = 9.46 x  10.15m

Micron = 10.-6m = 10.-4cm = 10.-3 mm

Angstrom (A*) = 10.-10m = 10.-8cm

Nanometer(nm) = 10.-9m = 10 A*

Fermi=10.-15m.

{ The radius of hydrogen atom is 0.5 a

The effective radius of  proton = 1.2 fermi}

PARSEC (Parallactic second)

It is a distance that corresponds to an annual parallax of one second due to rotation of the earth.

1 parsec = 3.26 light years

               = 3.26 x 9.46 x 10.15 m

               = 3.08 x 10.16m.

ATOMIC MASS UNIT (A.M.U)

1 a.m.u. = 1.66x 10.-27 kg

Weight = Mass x acceleration due to gravity.

W =m x g

Force = mass x acceleration 

F = m x a 

UNITS OF FORCE

MKS system = Newton

CGS system = dyne

FPS system poundal

RELATIONSHIPS

1 kg. Wt = 9.81 Newton 4

1 gm. Wt =981 dynes

1 pound wt = 32 poundals

PREFIX AND THEIR SYMBOLS FOR EXPRESSING POWER OF 10

Power of 10	Prefix	symbol
10.12	tera	T
10.9	giga	G
10.6	mega	M
10.3	kilo	K
10.2	hecto	H
10.1	deca	da
10.-1	deci	d
10.-2	centi	c
10.-3	milli	m
10.-6	micro	u
10.-9	nano	n
10.-12	pico	p
10.15	femto	f