EasyPhysics4u

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Give some examples of law of conservation of mass in our daily life

The following examples in our daily life shows the validity of law of conservation of

mass.

(i) In the heating of coal, the weight of remains ash is far less than the actual weight of coal. But this is apparent change in weight. If we weight the combining oxygen and the carbon before burning, and weigh the ash and carbon dioxide after burning, then in both cases the mass is same. Thus the total mass of reactants and the total mass of product remains constant.

(ii) Rusting of iron: When a piece of iron is placed in open air, a red layer of rust is formed. The mass of the iron piece increases. Rusting is the slow conservation of iron into its hydrated oxide in the presence of moisture and air.

4Fe +3O₂ =2Fe₂O₃

Fe₂O₃ +H₂O = Fe₂O₃ x H₂O

Where ‘x’ is any positive whole number. If we weigh the mass of iron, oxygen and water placed in a jar before rusting and after rusting the mass remains constant. Thus the law of conservation of mass valid in rusting of iron.

Energy : The capacity to do work is called energy.

Explaination : Energy is stored up work. A body is said to possess energy when it is capable of doing work. Thus, energy is measured by the total quantity of work that a body or a system of bodies can do.

Heat, sound, light, electricity are the examples of energy. Energy neither have volume nor contains mass and it also does not occupy any space. That is energy is not a matter but it is the capacity of doing work. We cannot see energy but can feel its existence like light ,we cannot see light but we can feel its existence when light falls on something , exactly like light we cannot see heat but can feel it.

Energy is a scalar quantity. It is measured by the amount of work that the body can do.

Unit: The CGS unit of energy is erg, SI unit is Joule ( J) and the bigger unit of energy are watt hour (Wh) and kilowatt hour(Kwh).

Different forms of energy: The following are the various forms of energy.

Mechanical energy, Heat energy, Light energy, Sound energy, Electric energy, Magnetic energy, Chemical energy, Nuclear energy ( or Atomic energy)**

LAW OF CONSERVATION OF MASS

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Explanations that how law of conservation of mass is obeyed in burning of a candle

When a candle burns, it forms carbon dioxide, water and some residue of melted wax. It seems that mass of candle is lost due to chemical change.
If we weigh the candle before burning and weigh all the products after
Burn the candle, we observe that there is no change in mass. We can verify this by Partigon experiment.

A hard and a long glass tube open at both end is taken. Through the upper part a mixture of quick lime and soda lime is packed over a copper gauge.Through the lower end of the tube a candle placed over a porous cork placed inside the tube. The entire arrangement (the tube with lime mixture and a candle) is placed on the left arm of the balanced and weighed carefully. The candle is now lighted and is quickly placed on the tube again, closing with porous cork.
After some time, when the candle burnt out completely, it has been found that the left arm of the balanced beam is tilted downward. It shows that there is a gain in mass during burning of the candle. This is because during combustion, carbon – dioxide and water produced are absorbed by the lime and sodalime. Again some oxygen from outside air through the porous of the cork has been used in the combustion increased the weight. Thus we observe that,
Mass of candle + mass of oxygen = mass of carbon dioxide + mass of water vapour
Or the total mass of the product = total mass of the reactants.
Thus, the law of conservation of mass is verified.

A little ash only remains as residue on burning a piece of magnesium wire.
Explain whether mass is conserved in this case.

Burning a piece of magnesium in air (or oxygen) is a chemical change. If we weight
the magnesium and the combined oxygen before reaction and after reaction, then there is no change in their mass.

The following experiment verify the law of conservation of mass.

Experiment : A hard test tube filled with oxygen and a tight fitted stopper is taken .
A small piece of magnesium is introduced in the closed tube contain oxygen and magnesium piece carefully. Now heat the test tube strongly by a Bunsen burner.
Magnesium piece burns brilliantly in the oxygen.

After cooling we find a white residue in the test tube. Weight the test tube again after reaction .We observe that the weight of the test tube before reaction and after complete reaction is the same. The magnesium piece reacts with oxygen form magnesium oxide.
2Mg + O₂ = 2MgO
Thus the weight of magnesium and oxygen before reaction and the weight of magnesium oxide after reaction is same. This verifies the law of conservation of mass.

MASS AND WEIGHT- DIFFERENCES

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Difference between Mass and Weight

Mass	Weight
The mass of a body is the matter contained in it .	The weight of a body is the product of its mass and acceleration due to gravity.
The mass of a body is always a constant quantity and does not change anywhere.	The weight of a body is a variable quantity and depends on the value of acceleration due to gravity.
Mass is a scalar quantity.	Weight is a vector quantity.
The mass of a body remains same at all places.	The weight of a body is zero at the centre of the earth.

Some general questions that a student may know for his/her knowledge

1.If the mass of a body on the earth is 10 kg then on moon the mass is 10 kg
The reason behind this is that mass remains same at all places .
Again the weight of the body changes at different on the earth with the variable value of acceleration due to gravity. It will be mg where m is the mass and g is acceleration due to gravity whose value on the earth is calculated approximately 9.8 m/sec², therefore weight =mg=10 x 9.8=98 N and its weight on the moon will be mg =10 x1.6=16 N because the value of g for the moon is 1.6 m/sec².

2. Is there any change in the weight of a body when it is taken from Kolkata
to Darjeeling explain this statement - The value of ‘g’ changes from place to place on the surface .The value of ‘g’ decreases with the rise of altitude(height). Since Darjeeling is situated at a higher altitude then Kolkata, hence the value of ‘g’ is less than Darjeeling with respect to Kolkata. Thus the body will experience less weight at Darjeeling then Kolkata.

Every thing in the universe obeys some laws regarding nature so mass is also a part of the universe it also obeys the same law.

Law of conservation of mass : The law of conservation of mass deals with the relation between the mass of reactants and the products during the chemical change. It was postulated by A. Lavoisier.

The law of conservation of mass states that during any physical or chemical change , the total mass of the product is equal to the total mass of the reactants
Or
matter is neither created nor destroyed during any physical or chemical change.

Verification of law of conservation of mass

Landoll’s experiment : In this experiment, take two solutions of sodium chloride and silver nitrate separately in the two limbs of H shaped tube (Landoll’s tube). Seal the tube and weight it. After weighing shake the tubes thoroughly to mix the solutions. The reaction occurs between the solution of silver nitrate and sodium chloride. A white precipitate of silver chloride is formed as ‘
AgNO₃ + NaCl = AgCl +NaNO₃
After the reaction weight the tube again. We will observe that the weight remains practically unchanged. This verify the law of conservation of mass.

MATTER AND ENERGY

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Matter : Anything which occupy some space , can be divide, and it can be perceived
By our sense organs (eye, nose, ear, tongue, and skin ) is called a matter.

Mass : Mass of a body is the total quantity of matter contained in the body.
Description : Each and every substance in the world , whether living or non-living is a matter. Mass is a constant quantity of a matter .
Mass of a body is measured with the help of a common balance .
Mass is a scalar quantity i.e it has only magnitude but no direction .
The C.G. S unit of mass is gm and S.I unit is Kg.

The fundamental properties of matter

The fundamental properties of a matter is given below;
·       Volume : Every matter living or non- living have a definite volume
·       Porosity : Every matter posses very minute porus , this property is called porosity.
·       Gravitation : Any two matter attract each other .
·       Divisibility : All matter can be divided into very small parts .
·       Inertia : An inainimate matter cannot , by itself , change its state of rest or Motoion.
·       Cohesion : Different molecule of the same substance attract each other.
·       Density : The mass of unit substance is called its density.

Weight of a body , how it is measured ,and its unit

Weight : The force with which the earth attracts the body towards its own centre is called the weight of the body.
The weight of a body is measured by a spring balance .
Weight of a body, being a force is a vector quantity. We know from Newton’s law of motion that force = mass x acceleration or P = mf.
In this case, the acceleration of the body is the acceleration due to gravity.Hence , if W be the weight of the body, then from the above definition W = mg , where ‘g’ is the acceleration due to gravity.
If g = 1, then m =W. Thus mass of a body is numerically equal to the weight of a body at a place of unit acceleration . At the centre of the earth g = 0 hence weight of a body is zero at the centre of the earth.

Units : Weight being a force, its S.I unit is Newton(N) and C.G.S unit is dyne . The gravitational unit of weight in S.I unit is Kilogram-force (Kgf) or Kilogram weight . In C.G.S system the unit of weight is gramme force (gf)
They are related as

1Kgf =1000 gf = 9.8 N
1gf =980 dynes , and
1 N = 10⁵ dynes where g =9.8 m/s²

METHOD OF MEASUREMENT OF DIFFERENT PHYSICAL QUANTITIES (3)

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Measurement of time

Time is measured by a wall clock, wrist watch, table clock. To measure a

fraction of time , stop watch is used.

Method of measurement of time by a clock

In our day to day life , time is measured by pendulum clock, whose function is based on the oscillation of a pendulum. In this type of clock, a metal rod is suspended from a rigid support. A heavy metal ball is suspended from the end of the rod. The time taken by the metal ball in one oscillation is regarded as 1 second. It consists of a circular dial which divided in 60 equal divisions.

Each division represents 1 minute. It is further divided into 12 equal parts, where each parts represents 1 hour. Hours are marked from 1 to 12 . In this clock long arm is the arm of minute and the short arm is the arm of hours. A spring is wound up with the help of key in old type of clock and by battery in digital clocks or battery operated clocks. The potential energy is converted to kinetic energy and rotates the arms of the clock.

Method of measurement of interval of time with the help of stop watch

Stop watch is used to measure the time interval between two events. It consists of a circular dial which is divided in 60 equal divisions. Each division represents 1 second. A long, light needle called second’s hand pivoted at the centre, rotates over the circular scale. A big circular dial also contains a small circular dial to read the time in minutes . The smaller dial graduated in 30 or 60 divisions and the small needle called the minute’s hand rotates over the scale. When the seconds hand completes one rotation, the minutes hand moves through one division or 1 minute.

A knob is provided at the top of the frame for winding the watch. By pressing the

Knob in succession, the watch can be started, stopped and both the needles can be

Brought to searting point for future use.

METHOD OF MEASUREMENT OF DIFFERENT PHYSICAL QUANTITIES (2)

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Method for the measurement of volume of a liquid

The space occupied by a body is called the volume of that body.
The volume of a liquid in the laboratory is measured by the following
Measuring devices.
1.    Measuring cylinder
2.    Measuring flasks
3.    Burette
4.    Pipette
Measuring cylinder is commonly used to measure the volume of a liquid. It is
a glass cylinder of uniform radius. The outer wall is graduated in cubic centimetre
and millimeter from the bottom upwards. It is available in different sizes. Before
measuring the volume of a liquid through measuring cylinder it is cleaned and
kept fixed vertically. The liquid whose volume has to measure is poured in it
and the reading of upper layer of the liquid is noted. This reading is the volume
of the liquid.

To determine the volume of an irregular solid heavier than and insoluble in water
                                 With the hep of measuring cylinder

To find the volume of an irregular shape of solid body, we take a graduated
cylinder. Fill the cylinder partly with water. Note the reading of the lower level of
water(say x₁ cc). Now tie the given solid with a thin string and lower it gently into the cylinder so that the solid is completely immersed in water. The level of water is rises again.
Note the new reading of the water level raised (say x₂cc).
Since the body displaces water equal to its volume , Hence the volume of
Solid body = second reading – first reading
Thus , volume of solid = (x₂ - x₁) cubic centimeters.

To find the density of an irregular shaped body insoluble in water.

Density: The density of a substance is defined as its mass per unit volume
Density is a scalar quantity and represented by the letter ‘d ’. If the mass of a body be M gms, and the volume of the body is V cubic cms, then
d = M/V. Its unit is gm per cm³. SI unit is kg /m³.
To find the density of an irregular body , first find the mass of the body by common balance . Now find the volume of the body by the following steps.
To find the volume of an irregular shape of solid body, we take a graduated
cylinder. Fill the cylinder partly with water. Note the reading of the lower level of
water(say x₁ cc). Now tie the given solid with a thin string and lower it gently into the cylinder so that the solid is completely immersed in water. The level of water is rises again.
Note the new reading of the water level raised (say x₂cc).
Since the body displaces water equal to its volume , Hence the volume of
Solid body = second reading – first reading
Thus , volume of solid = (x₂ - x₁) cubic centimeters.
Dividing Mass of the body by volume we get the density of the body.

Measurement of volume of a regular shaped body is determined

To find the volume of a regular shaped body its dimensions such as length, breadth, height, radius etc, are measured . Then use the following relations:

Volume of cuboid = length x breadth x height
Volume of cube = (side)³
Volume of sphere =4 / 3 π (radius)³

METHOD OF MEASUREMENT OF DIFFERENT METHOD OF MEASUREMENT OF DIFFERENT PHYSICAL QUANTITIES

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Method for the measurement of length with the help of ordinary scale.

Ordinary scale is a device used to measure the length of an object.
Ordinary scale is generally made up by wood, metal or plastic. It is graduated in centimeters, millimeters. 1 centimeter is divided into 10 equal parts, each part is 1 millimeter.
To measure the length of a line say AB, we place the scale in such a way that it remains perpendicular to the line AB. Now note the reading of the starting point and the end point B from the scale.
Then, Length of line AB = Reading of end B – Reading of end A
As per example: Let the starting point A of the line AB is at 2 cm, coincide with the scale. If the end point B of the line does not coincide exactly with the graduation of the scale, the reading has to be taken by eye approximation method. While taking the reading eye should be placed directly above the point B. Let the end B coincide with the scale at 6.5 cm .
Therefore length of the line AB = 6.5cm -2cm = 4 .5 cm.

Method for the measurement of mass with the help of a common balance

Common balance is an instrument used to measure the mass of a body.
By common balance we find the mass of a body by comparing its mass with some known standard weights. Generally we put the body on the left pan of the balance whose mass is to be determine and the standard weights are placed on the right pan. When the beam of the balance becomes horizontal then the mass of the body is equal to the standard weight.

Method for the measurement of mass with the help of a spring balance

Spring balance is a type of balance used to measure the weight of a body.
It consists of a spring kept in a metal tube. It is partially exposed in front of the metal tube. The upper end of the spring is rigidly fixed. The lower end of the spring is attached with a metal rod. One hook is attached with the lower end of the metal rod. The body whose weight is to be determined is hanged from this hook. A pointer attached to the spring moves on a graduated scale (usually in grams or kilograms and grams ). The position of the pointer indicates the weight of the body.

2012-08-21T15:09:00.000+05:30

Introduction

What is Physics?

The word physics comes from the Greek scripted word Physis which means Nature.

It is only based upon the natural phenomenon.So while you are going to study physics just keep in mind that you are studying about the nature .The things which are happening in the nature the thing which are happening around and you are associated with the facts.

Starting the study of physics we should know some small but knowledgeable things.

Are you readdy

be calm ,keep patient.

Defination of physics : The branch of science which deals about the study of natural phenomenon is known as physics.

Modern defination of physics-The branch of science which deals with the study of Matter,Energy,Light, optics,Electromagnetic waves

is known as physics.

Choosing correct units and Dimension of Physical quantity

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Explain the reason of using different smaller and larger units for measuring a particular quantity.

To measure a particular quantity we use both smaller and larger units as per requirement. For example. To measure the length of a room , we use metre(m) to measure the distance between two cities we use kilomete(km). For the measurement of the distance of a star from the earth the commonly used unit is light year. Because kilometer is considered to be a very small unit in this case.

To measure the length of a very small quantity we consider smaller unit of lengths as centimetre, millimeter, micron etc. For example to measure the thickness (or diameter) of a wire, we use centimetre or millimeters. In this case unit taken as metre is absurd. If the thickness of a paper measured in millimeter(mm) is 1 mm, then expressed in metre is 0.001 m, which look odd.
Therefore we should carefully examine that what unit we have to take for the measurement of a thing . If we chose a thing to measure we should take its standard unit.

Dimension of a physical quantity
Having defined the units of physical quantities, we now briefly mention the concept of dimensions of other physical quantities.
The dimension of a physical quantity is represents the powers to which the fundamental units have raised in order to obtain the derived units of the physical quantity.
The dimensions of length, mass and time are expressed in L, M and T’ respectively. Dimensions generally represents the nature of the units only. It does not indicate the magnitude of the units.

Discussion : Speed has the derived units –cm/sec., km/hr., mi/hr. etc. The most common feature in them is that they all are derived by dividing a unit of length by a unit of time. So the dimension of speed will be L/T or LT^-1 where ‘L’ stands for length and ‘T’ stands for time. Similarly different units of acceleration e.g ., cm/sec², ft/sec², mi/hr² etc. represents a unit of length divided by square of unit of time. Hence its dimension will be L/T² or L/T ^-2.
Following the same reasoning ,force which is the product of mass(M) and
aceleration (LT^-2), has the dimension MLT ^-2.

Measuring Instruments

As the measurement of length, volume, mass and time was thoroughly taken into consideration in the previous article, we shall not go through it any more.

In this article we shall rather present a brief description of some appliances for measurement of length which enables greater accuracy to be obtained than is possible by mere eye-estimation.

To measure the different physical quantities, the commonly used measuring devices are the following.
1. Ordinary scale (metre scale) use to measure the length of an object.

2. Common balance - it is used to measure the mass of a body.

3. Spring balance – it is used to measure the weight of a body.

4. Measuring cylinder – it is used to measure the volume of a body a liquid.
It is also used to measure the volume of a solid by displacement method.

5. Clock – it is used to measure the time.

6. Stop watch – it is used to measure a time interval between two events such as race, sports , football etc.

System of Units

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System of Units

A complete sets of units, both fundamental and derived, for all physical quantities is called a system of units. There are now mainly three systems
in common use, each of which derives its name from the initial letters of the fundamental units upon which it is based. These are:

(1 C.G.S. system, having centimetre, gram and second a fundamental units .
(2) M.K.S system, in which fundamental units are metre, kilogram and second.
(3) F.P.S system, based on foot,pound and second as fundamental units.

A fourth system of unit, namely S.I., (systeme internationale) is introduced in 1960, is described in the appendix.

The first two namely C.G.S. and M.K.S. systems are also called metric system
and obviously metric standards of length and mass are used in them.

The F.P.S on the other hand based on the British standards.

The metric system has a definite advantage over the F.P.S. system calculations
are made easier , since the various multiples and submultiples of unit are
related by simple power of 10 .

On the other hand the F.P.S system has however , no such advantage .The
relation between the various subdivisions of a unit are rather obscure and inconvenient , such as 1 foot =12 inches ,1 yard =3 feet, 1 mile=1760 yds.
Even an inch is divided into 8ths, 16ths, 64ths to measure very small lengths.
Units of volumes of liquids.

The unit of volume of liquids, through derived ones, should be mentioned
especially, since these have different names. Thus , in metric system unit of volume is litre which is defined as the volume of 1 kg of water, at normal atmospheric pressur and the temperature of its maximum density (at 4^°C).

Standard.

A question still remains weather there is a unique standard for a particular fundamental quantity . Unfortunately, the answer is ‘no’. World is still divided into two major portions using two different standards for each of length and mass.
     In metric system the standard of length is taken as the distance between two fine lines engraved on a platinum-irridium bar kept at International Bureau of Weight and Measures in Paris maintained at 0^°C and called International Proto-type Metre.

Defination of Metre: A metre is defined as 1,553,164.1 times the waves length of the red line in the spectrum of cadmium.

Defination of Kilogram : International Proto-type Kilogram is the standard of mass in the metric system and is defined as the mass of a platinum-irridium cylinder kept together with Proto-type metre at Serves near Paris ,and the copies being distributed all over the world .It was also intended to be the mass of 1000 cc. of water at its maximum density.

Defination of second : The standard of time called mean solar second (second) is the same in both systems and is defined as 1/86400 of the average length of a solar day (mean solar day) throughout the year. This definition of a second , although
Satisfactory for our daily routine, fails to satisfy modern scientist since the mean solar day varies from year to year and century to century.
Hence, in 1946, International Bureau of Weights and Measures defined the second as the time in which a cesium atom(which has only one isotope) undergoes 9,192,631,770 internal vibrations.

There are also some bigger units of length they are namely

1. Kilometer(km)             2. Light year             3. Astronomical unit(AU)

1 kilomatre is equal to 1000 metre
i.e 1 kg = 1000 m or(10³m)

2. 1 Light year is the distance traveled by light in Vaccum in one year.
     1 Light year = Speed of light x 1 year
                           = 3x10³m/s x 1 year
                           = 3x10³m/s x (365x24x60x60)s
                           =9.46x10¹² km
3. Astronomical unit(AU) : It is defined as the distance of the earth from the
     sun.
        1 A.U =1.499x 10metre.

Smaller units of length . There are some smaller units of length they are
                                             namely, (SI unit of length is metre)

     1 metre = 100 cm =1/100m
     1 metre = 1000mm=1/1000m
     1 metre = 1000000 micron or 1 micron =10^-6 m
    1 Nanometre =10^-9m

Classification of physical quantity

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How a physical quantity can be classified?

A physical quantity can be classified into two broad categories:

(i)Scalar quantity (ii) Vector quantity

Scalar quantity: The physical quantities which have only magnitude but no direction are called scalar quantity.

Description: The rod is 2 metres long’, the vessel contains 200 gms. Of water’ and we waited there for five hours’. In these expressions , 2 metre long , five hours , 200 gms , we have some ideas of magnitude of a length , mass , and a time . But length mass and time has nothing to do with any direction. Such quantities which gives the idea of some magnitude but are not associated with any direction are called scalar quantities.

Example : Volume, density, energy, , speed , mass, distance, work, time, power, electric current , mechanical advantage , pressure, etc are the examples of scalar quantities.

Vector quantity : The physical quantities which have magnitude as well as direction is called vector quantity.

Description: The car is moving is moving with a velocity of 40 km/hr ‘east’

here east is representing the direction of the car and 40 represents the magnitude of the car .So in this example both magnitude and direction are coming so definitely it is a vector quantity, because it fulfils the condition to be a vector . A very important thing with regard to vector is that it is represented by an arrow sign (→ ). If in a problem vector word is not mentioned but the arrow sign (→ ) is there it is a vector quantity.

Example : Displacement, velocity, acceleration, momentum, force, weight, temperature, electric field , magnetic field, retardation ,moment of force etc.

What observation should be taken for the choice of unit ?

The selection of unit to measure a physical quantity should have the following properties.

1.The unit should be convenient size.

2.The unit should be well defined .

3.The unit should not be changed with space , time and temperature.

4. It should be reproducible.

Fundamental quantities and derived quantities

Each of the various physical quantities is expected to have its own unit and a standard. But is found that nearly all physical quantities(except temperature,

Electric current and luminous intensity)can be derived from the units of three

physical quantities , namely, length, mass , time.

Fundamental quantity : The quantities which are independent of any other quantity or which can neither be changed nor be related to any other quantity

are called fundamental quantities.

Example : Length, mass, time, temperature, current, luminous intensity atc are the examples of fundamental quantities.

Derived quantities : The quantities which depend upon the fundamental quantities or which can be expressed in terms of the fundamental quantities i.e derived from the fundamental quantities are called derived quantities.

Example : velocity, acceleration, energy, force, momentum, etc are the exaples of derived quantities.

Discussion :The velocity of a moving body is obtained by dividing the distance traveled by the body with time taken to travel the distance . When distance is expressed in the unit of length as centimetres and time is expressed in seconds then,

,unit of velocity = unit of length / unit of time = cm/second=cm/sec.

MEASUREMENT AND THEIR DEVICES

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SYSTEM OF MEASUREMENT AND MEASURING DEVICES

By saying measurement a question arise in the mind that what is measurement?. The answer is as simple is that measurement is the numerical value multiplied by its unit.

Lets begin our study.

Some basic knowledge you have to acquire.

What is physical Quantity?

The quantities which we can measure are called physical quantity.

It is the measurable property of a matter. As per example, length, mass, density, velocity are all physical quantity because they all can be measured .For the measurement of a physical quantity we must know two basic things.

(i)The unit in which the quantity is to be measure

Example: If we have 10 kg of mangoes and we are measuring in litre it is not the right process we have to measure it in the unit of Kg not in liter.

(ii) The numerical value which express how many times the unit used

is contained the given quantity.

What is unit?

To measure any physical quantity, we must first have a unit of measurement. By unit of a physical quantity we mean a definite and convenient amount of that quantity. The magnitude of a physical quantity is obtained by comparing it with the unit.The factor by which a quantity is bigger or smaller than the corresponding unit is called the numerical measurement of that quantity. As per example “a room is 5 metre long clearly showing that the physical quantity being measured is length, and the unit chosen for measuring the room is metre and the numerical value is 5.

In the previous para we have seen that the unit of length is metre. But what is a metre? To define it we evidently require a standard length. Similarly we require a standard for every other unit. A standard is the physical embodiment of a unit. It fixes up and preserves the size of the corresponding unit. A unit may be of same size as that of the standard or may me a multiple or submultiple of it. The standard Proto-type of kilogram is the standard of mass, the units of mass being kilogram(kg.), metric ton(10³kg.), gram(10^-3kg.) etc.

All physical quantities have units?

The answer or this question is as simple is that there are many physical quantities which does not have any units .The question arise in the mind that if a thing is in the category its first condition is that it would be measurable

And for measuring a unit is required so how a quantity is physical but not measurable . As in the field of physics there are some physical quantities that does not have any units there are the exceptions like six fingers in one hand of a human ,The reason is that for a non-unit physical quantity that those physical quantities which are expressed as the ratio of the same physical quantity do not have units .

Example : atomic weight of elements, specific gravity, refractive index.

2012-08-16T20:37:00.000+05:30

Introduction

What is Physics?

The word physics comes from the Greek scripted word Physis which means Nature.

Starting the study of physics we should know some small but knowledgeable things.

Are you readdy

be calm ,keep patient.

Defination of physics : The branch of science which deals about the study of natural phenomenon is known as physics.

Modern defination of physics-The branch of science which deals with the study of Matter,Energy,Light,

optics, Electromagnetic waves is known as physics.

Details- It is related to the study of matter and energy and how they interact each other.

Physics cannot exist without a physicists ther are the one who discovered the basic laws related to physics.There are the names of some physicists who work for the benefits of physics and gave physics its real position.

Albert Einstein

Brian Cox

Newton

Branch of physics – Before studying physics we should know how it is divided . As we know that there are many branches of science so there exist different branches of physics also.

I am listing you the different branches of physics.

		Mechanics
Heat	*Magnetism*	*Current Electricity*	*Optics*
*Electrostatics*	*General properties of matter*	*Vibrations and Waves*	*Modern Physics*