पाठ्यपुस्तक डाउनलोड गर्नको लागि लिंक लगायत कक्षा ९ र १० को लागि पूर्व मूल्यांकन परीक्षा लिंक

 Class 9

Unit 1: Measurement

Measurement and it's importance:

The process of comparing unknown physical quantity with a known standard quantity is called measurement. The importance of measurement are as follows:

1. It is essential in trade i.e. selling, buying and exchanging of goods.
2. It is required in performing daily life activities.
3. Measurement of medicine is a must for the proper treatment of diseases.
4. It is essential for scientific experiments while collecting data and information.
5. Measurement plays an important role in the manufacturing of goods such as clothes, food items

Watch this video: fundamental and derived quantities

Unit and its types:

A unit is defined as a convention to define an amount of physical property in a specific system of units.

Units are of two types:

1. Fundamental units
2. Derived units

Fundamental units:

The units of the fundamental quantities are called fundamental unit. Those units which are independent cannot be derived from other unit is called fundamental unit.

Physical Quantity	Unit	Symbol
mass	kilogram	kg
length	meter	m
time	second	s
temperature	Kelvin	K
electric current	ampere	A
amount of substance	mole	mol
luminous intensity	candela	Cd

Derived units:

Derived units are composed of the fundamental units and are originated from the products and ratios of the fundamental units. Derived units belong to physical quantities that are derived from basic physical properties. Examples are:

Velocity – a physical quantity derived from fundamental quantities of length and time

               velocity  = distance / time  = m/s 

So the units of velocity is ms-1

Some derived units:

Volume: cubic meter, Force: Newton, Pressure: watt, Frequency: hertz, Work: Joule etc.

Fundamental unit	Derived unit
1) The units of the fundamental quantities are called fundamental unit. 2) e.g kilogram , meter,  second are the fundamental units	1) The units which are derived from the fundamental units are called derived units. 2) Newton, joules   are the derived units.

SI Units and its Significance:

The units used in SI system are called SI units (System international de units). For example, meter is the unit of length and kilogram is the unit of mass. 

significance:

1. The system of SI units has bought uniformity and similarity in measurement all over the world.
2. Each units has its sub multiples and multiples. This helps in taking any magnitude of measurement.
3. It is a coherent system of units. That is, in this system, all the derived units can be easily obtained from fundamental units.

Measurement of mass:

The total quantity of matter contained in a body is called mass. The SI unit of mass is Kg. It is measured by beam balance.

One standard kilogram is defined as the mass of platinum-iridium cylinder kept at International Bureau of Weight and Measures at Severs (near Paris)

Measurement of Time:

The interval or duration between any two events is called time.SI unit of time is seconds (sec.). It is measured by using watches and clocks.

The time taken by the earth to rotate once in its own axis is called one mean solar day. It is equal to 24 hours. The point in the space just above the observer's head is called Zenith.

One second is defined as 1/86,400 part of a mean solar day.

One standard second is defined as the time required to make 9192631770 vibrations by cesium - 133 atom.

Time measuring devices:

• Mechanical or automatic or pendulum clock
• Quartz clock
• Electronic clock
• Atomic clock

Measurement of area:

fig: area of leaf (irregular body)

The total space occupied by a plane surface is called area. SI unit is square meter. We can measure the area of regular bodies by using formula.

The area of irregular bodies such as leaf, broken glasses can be measured by using graph paper.

Measurement of Volume:

fig: Volume of stone (irregular body) by measuring cylinder

The total space occupied by a body is called volume. The SI unit of volume is cubic meter. The volume of regular bodies can be measured by using formula.

The volume of irregular bodies like stone is measured by measuring cylinder.

Ten to power notation or Scientific notation:

While measuring the amount of physical quantities, we sometimes get too large or too small values as the result. In such case, the number should be written in ten power of notation. For, example, 0.000000001 kg is written as  kg.

Scientific notation is useful because 

• it allows us to easily write and make calculations with extremely small and extremely large numbers.
• It helps in saving time and increases accuracy.
• It also helps to save space.

Assignment:

👉Liveworksheets (two sets)

Dear students, do these two sets,

For this:

• write your name, class
• do all questions
• click on "finish" at the bottom of the page
• click on "email my answer to the teacher"
• Enter your full name, grade/level, subject
• In teacher's key code or email, Enter:  eg1mn5iriqr
• And, the click on "send"
• Scroll up, at the top of paper, you will get score for objective answer type questions.
  Measurement (objective test), an interactive worksheet by thapasunil
  liveworksheets.com

👉Watch this video and write answer in comment: (To write answer, first write your name and write question no. and then answer)

Question: Quartz clock gives more accurate time than that of pendulum clock. Why?

 Class 10

Unit 1: Force

Force:

Force is defined as a push or pulls that change or tends to the state of the body whether it is
 at rest or in uniform motion along the straight line. Force is a vector quantity. 

 

 

Newton law of gravitational: 

Newton’s Law of Gravitation states that “The force of attraction between the two bodies is 

directly proportional to the product of their masses and inversely proportional to the 

square of the distance between their centers.” Newton’s law of the gravitation holds true or 

applicable for all the objects present in this universe whether the objects be 

terrestrial or celestial. The gravitational force exists everywhere in this universe.

Therefore Newton’s law of gravitation is called universe law.

 Verification of Newton’s law of motion:

Consider the two bodies of the mass M1 and M2with force F acting between them towards
their centre.  If the distance between their centers is d then,

 
According to Newton’s universal law of gravitation,
We have F ∝  M1M2……1
F ∝   1/d2
Combining I and 2 we get F  ∝   M1 M2/d2
F=GM1M2/d2
Where G is proportionality constant which is known as universal gravitational constant.
The numerical value of gravitational constant (G) is 6.67*10-11 and its unit is Nm2/Kg2
 
Properties of G:

Value of G is independent of the temperature, pressure, nature of the intervening medium
and chemical composition of the masses of the bodies.                       

Gravity:
It is the force which pulls an object towards the centre of the earth.
 

Acceleration due to gravity: The acceleration produced in a freely falling body due to the
influence of gravity is called Acceleration due to gravity.
It's symbol is “g” and its SI unit is meter per second (m/s2).

 
Relation between acceleration due to gravity and radius of the earth

Let 'M 'be the mass and 'R 'be the radius of the earth and 'm' be the mass of the body kept at
the surface of the earth

According to the Newton’s law of gravitation the force of attraction between them is given by
 
F=G Mm/R2………………………1
Also the body is attracted towards the centre of the earth with a force given by
F=mg…………………..2
From 1 and 2, mg = G Mm /R2
g=GM/R2…………….3
'G' and 'M' are constant whereas 'R' varies because radius of the earth is more at the equator

than at poles.

From 3,
We can say that the acceleration due to the gravity is independent to the mass of the body

but depends on the mass and radius of the earth.

 
Variation of the value of g:

a. Variation due to the shape of the earth: g ∝ 1/R2
   Value of the g maximum at poles but minimum at equator
b. Variation due to the height from the surface of the earth: g’ = (R/R+h) 2 g
If we increase the height from the surface of the earth the quantity in the bracket becomes
less than 1.
And the acceleration due to the gravity decreases as height from the surface is increased.
c. Variation from the depth of earth surface: g’ = g(R-x)/R since the quantity
 (R-x)/R is less than 1 .The value of g inside the earth decreases with increase in depth.
At centre of the earth x=R so gravity at the centre of the earth is 0

 
Gravitational field and Gravitational field intensity:

The space around the mass where gravitational force of influence of the mass can be felt is
called gravitational field.
Gravitational field intensity is the force experienced by the unit mass kept at that point.
It is given by
Gravitational Field intensity (I) = Forced experienced / mass
If the body of mass m is kept at the distance d from the centre of the earth of mass M and
radius R
Figure:
 
Them force experienced by the mass is given by
F = G Mm/d2
To calculate the gravitational field intensity we have to take a unit mass so m =1
Gravitational field intensity (I) = GM/d2
If the body is at the surface of the earth d = R
(I) = G M/R2
This is numerically equal to the acceleration due to gravity.
 
Mass: It is the quantity of matter contained in the body. It is scalar quantity.

Weight: It is the force with which the object is attracted towards the centre of the earth. It is
vector quantity.
Weight=mass * gravity. Weight depends upon gravity and gravity depends on the distance.
E.g. As the stone is away from the earth surface the weight of the stone is less than the
stone present in the bottom.

Free fall: When an object is falling towards the surface of the earth only under the influence
of gravity without external resistance, the fall of the object is free fall.
Weightlessness: Weightlessness is the condition at which the apparent weight of a body is
zero. Weightlessness is possible in the absence of gravity.

Some solved numerical problems: (Questions 1, 2, 3 not 1, 4, 5)

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Assignment:

👉Watch this video and write answer in comment: (To write answer, first write your name and write question no. and then answer)

Questions: 1) What is free fall ? Write any two examples.

2) What are the conditions of weightlessness? Write any two conditions.

👉Do this liveworksheets.

For this,

• write your name, class
• do all questions
• click on "finish" at the bottom of the page
• click on "email my answer to the teacher"
• Enter your full name, grade/level, subject
• In teacher's key code or email, Enter:  eg1mn5iriqr
• And, the click on "send"
• Scroll up, at the top of paper, you will get score for objective answer type questions.

Force, an interactive worksheet by thapasunil
liveworksheets.com