# Physics 9th | Motion: Displacement

## Motion: Displacement

### Motion

1. A body is said to be in motion if it changes its position with time with respect to the observer.

e.g. When a tree T is observed by an observer A sitting on a bench, the tree is at rest. This is because the position of the tree is not changing with respect to the observer A.

Now when the same tree T is observed by an observer B sitting in a train moving with a velocity V, then the tree is moving with respect to the observer B because the position of the tree is changing with respect to the observer B.

So we always need a reference point to explain the motion. In case 1, the reference point is the observer A, while in second case, reference point may be observer B.

### Type of Motion

(i) Linear motion

(ii) Circular motion

(iii) Vibratory motion

#### (i) Linear motion:-

The motion of a body is said to be linear motion If the body moves in a straight line or path.

e.g. Motion of a moving car on a straight road.

Motion of a ball dropped from the roof of a building.

#### (ii) Circular Motion: –

The motion of a body is said to be circular motion if the body moves around a fixed point.

e.g Motion of an electric fan

Motion of a spinning top

#### (iii) Vibratory motion: –

The motion of a body is said to be vibratory motion if the body moves to and fro about a fixed point.

e.g. Motion of a pendulum

Motion of a swing

### Nature of Motion

(i) Uniform motion

(ii) Non- uniform motion.

#### (i) Uniform motion: –

The motion of a body is said to be uniform if the body covers equal distance in equal interval of time.

e.g.

#### (ii) Non- Uniform motion: –

The motion of a body is said to be non-uniform if the body covers unequal distances in equal interval of time.

eg.

### Scalar quantity:

The physical quantity which has only magnitude and no sense of direction is called scalar quantity.

e.g. distance, speed , time, work, etc.

### Vector quantity: –

The physical quantity which has both magnitude as well as direction is called vector quantity.

e.g. displacement, force, momentum, etc.

### Distance: –

The actual length of path covered by a moving body between its initial and final position is called the distance covered by the body. It has no sense of direction.

It is a scalar quantity and its S.I. unit is meter (m)

### Displacement:

The shortest distance between the initial and final position of a moving body is called the displacement of the body and is directed from the initial to the final position

It is a vector quantity & its S.I unit is metre (m)

Distance will be equal to displacement if the body moves in a straight line, otherwise distance will be greater than displacement

i.e. Distance Displacement

### Difference between distance and displacement

 Distance Displacement 1. The actual length of path covered by a moving body between its initial and final position is called the distance covered by the body. 2. It has no sense of direction. 3. Distance is a scalar quantity. 4. It is always positive. 5. It can not be zero for a moving body. 1. The shortest distance between initial and final position of a moving body is called the displacement of the body and is directed from initial to final position 2. Direction is associated with displacement. 3. Displacement is a vector quantity. 4. It can be positive or negative. 5. It can be zero if initial an final position of the body is same.

# Chemistry IX | Matter-Its Nature and Behaviour | Part 1

## INTRODUCTION

### Matter

· Anything that occupies space , possesses mass and exert pressure is called matter.

### Element

· An element is a substance which cannot be split up into two or more simpler substances by the any chemical and physical methods of applying heat, light or electric energy.

· There are 114 elements known at present, out of which 92 elements occur in nature, while remaining 23 elements have been prepared artificially.

### Metals

· The elements which have a tendency to form positive ions (by loss of electrons) are known as metals e.g. silver, tin, zinc etc.

· Metals are elements having lustre ductility, malleability, conductivity etc.

· Aluminium is the most abundant metal in the earth crust.

### Non-metals

· The elements which have a tendency to form negative ion by gain of electrons are called non-metals e.g. hydrogen oxygen, sulphur etc.

· Oxides of non-metals are neutral (in low oxidation state) or acidic (in higher oxidation states) in nature.

· They are in powder or gaseous form under normal conditions.

· Bromine is the only the non-metal which is liquid under normal conditions.

### Metalloids

· They are the elements whose properties fall between those of metals and non-metals. E.g. germanium, arsenic, selenium and tellurium etc.

### Symbols

· The short form used in place of full name of an element is called its symbol.

· The symbol of an element is the ‘first letter’ or the ‘first letter and another letter’ of the English name or Latin name of the element. Symbols derived from English name of the elements.

 English name of the element Symbol English name of the element Symbol Argon Bromine Hydrogen Helium Krypton Lithium Ar Br H He Kr Li Manganese Neon Phosphorus Silicon Zinc Magnesium Mn Ne P Si Zn Mg

### Symbols derived from Latin names of elements

 English name of the element Symbol Latin name of the element Copper Gold Iron Lead Mercury Potassium Silver Sodium Tin Tungsten Cu Au Fe Pb Hg K Ag Na Sn W Cuprum Aurum Ferrum Plumbsum Hydrargysum Kalium Argentum Natrium Stannum Wolfarm

### Mixture

· A mixture is a substance which consists of two or more elements or compound not chemically combined together e.g., air milk, ink, brine, lime water, glass paints, soil, food, wood, kerosene etc.

### Types of Mixture :

Mixtures are of two types.

### Homogeneous mixture :

A homogeneous mixture has a same composition throughout its mass. It has no visible boundaries of separation between the various constituents e.g., solution of sugar in water, solution of salt in water, a mixture of alcohol and water etc.

### Heterogeneous Mixture :

A heterogeneous mixture which does not have a uniform composition throughout its mass. A heterogeneous mixture has visible boundaries of separation between the various components. E.g., solution of K2Cr2O7 in water, solution of CaCO3 in water, solution of oil in water, gun powder, soil, etc

· A mixture which boils at a definite boiling point are called azeotrpic mixtures.

### Properties of a Mixture

· A mixture can be separated into its components by physical methods like, filteration, evaporation, sublimation, distillation, magnet etc.

· A mixture shows the properties of all the constituents present in it.

· Energy is usually neither given out not absorbed during the preparation of a mixture.

· The composition of a mixture is variable i.e. the constituents can be present in any proportion by weight.

· A mixture does not have a definite melting point, boiling point etc (except azeotrpic mixture).

### Methods of Separation of Mixture

#### 1. Crystallization :

This method is based on the difference in the solubility of the various compound and in a solvent. E.g., a mixture of KNO3 and NaCl can be separated by this process.

#### 2. Distillation :

This method is used for the purification of liquids which boil without decomposition and contain non-volatile impurities e.g., pure water can be obtained from sea water by distillation.

#### 3. Fractional distillation :

This process is used to separate a mixture of two or more miscible liquids which have boiling point close to each other. e.g., petrol, diesel, kerosene.

#### 4. Sublimation :

This process is used for the separation of those solids which sublime from a non-volatile solid. This process is generally used for the separation of naphthalene anthracene, benzoic acid, camphor, NH4Cl, iodine etc.

#### 5. Distillation under reduced pressure :

It is used for liquids which decompose below their boiling point. It is also called vacuum distillation e.g., glycerol can be separated by this method.

#### 6. Steam distillation :

It is used for the separation and purification of liquids which are appreciably volatile in steam from non-volatile components of mixture e.g., o-nitrophenol and p-nitrophenol are separated by this method. Aniline is also purified by this method.

#### 7. Evaporation :

It is the process by which soluble solids can be obtained from their solution by allowing the solvent to vaporize e.g. salt can be obtained from salts solution be evaporation.

#### 8. Chromatography :

Chromatography is a modern method proposed by Iswett in 1903. This method is based on the difference in the rates at which the components of a mixture are adsorbed on a suitable adsorbent. This method has been used to separate ortho and para-nitrophenol, to separate blue and red dyes, to separate plant pigment sand other natural products.

#### 9. Atmolysis :

It is used for separating the mixture of gases. This method is based on the difference in their rates of diffusion.