9th Class

Atoms and Molecules   Matter is made up of small particles called molecules. Atoms combine to form molecule. Different atoms and molecules have different properties due to which different matters show different properties.   Laws of Chemical Combination The laws of chemical combination are:  

• Law of conservation of mass
• Law of constant proportions

  Law of Conservation of Mass This law states that in a chemical reaction, the total mass of products is equal to the total mass of reactants. There occurs no change in mass during a chemical reaction. For example, in the following chemical reaction:   Sodium carbonate + ethanoic acid \[\to \] sodium ethanoate + carbon dioxide + water             The addition of mass of sodium carbonate and ethanoic acid will be equal to the addition of mass of sodium ethanoate, carbon more...

Cells and Tissues   Cell Tie cell is the basic structural and functional unit of living organisms. All living organisms are made up of the smallest unit that is cell. The organisms can be of two types unicellular and multicellular. The unicellular organisms such as amoeba, Paramecium has a single cell in their body and this single cell performs all basic life activities. The multicellular organisms such as human beings have millions of cells in their body. Most of these cells are specialised to carry out a few functions efficiently. A group of cells is responsible for performing a specific function. For example, muscle cells contract and relax to cause movement of a body part.   Structure of a Cell Different cells have different types of structures which depends on their specific functions. The size, shape, number and volume vary largely in multicellular and more...

Diversity in Living Organisms   Diversity in Living Organism This world is full of living and non-living things. Large variety of living organisms is found on this planet. There is a great diversity among them. From the microorganisms to well-developed animals, one can notice the diversity at all levels.   Basis of Classification Classification is a method of arranging organisms into groups or sets on the basis of similarities and differences. The study of classification is known as taxonomy. The process of classification began hundreds of years ago. First animals were classified according to whether they lived on land, in water or in the air, but this classification was not adequate. So the need of more accurate form of classification was realised and thus some characteristics were used as a basis for making the broadest divisions for making groups and subgroups.   Classification and more...

Force and Motion   Motion The movement of a body is called motion. The body that is in motion changes its position with time. Therefore, a body is said to be in motion when its position changes continuously with respect to a stationary object taken as a reference point.   Distance The distance travelled by a body is the actual length of the path covered by a moving body irrespective of the direction in which body travels.   Displacement When a body moves from one position to another position, the shortest distance between initial and final position of the body along with the direction is known as its displacement.                        more...

Gravitation   Gravitation When we throw .an object in upward direction it comes down automatically. This happens because of the force of gravitation. Actually the earth exerts a force of attraction that is called gravity on the object and pulls it down. Isaac newton   The gravitational force was discovered by Sir Isaac Newton. One day he was sitting under an apple tree, suddenly an apple fell down from the tree. He started thinking about it. He concluded that the earth has certain force that attracted the apple. Finally he concluded that the earth attracts all the objects towards its centre and this force of attraction is called gravitational force of the earth or the gravity. The gravitational force of the earth is responsible for many phenomenons that take place around us. more...

Work, Energy and Sound   Work In Physics work refers to any activity that produce motion. Work is done only when the resultant force and displacement are not zero. The amount of work done by a particular force largely depends on the two factors that are magnitude of the force applied and displacement of the body. We can say that work done in moving a body is equal to the product of force exerted on the body and the displacement moved by the body in the direction of force. \[Work=Force~\times Displacement\] OR \[W=F\times S\] The S.I. unit of work is joule. If a force of 1 Newton moves a body through a displacement of 1 m in its own direction then the work done is known as 1 joule. 1 joule\[=1\,\,N\times 1\,\,m\] Work is a scalar quantity. When a ball is thrown up, its more...

Why do we fall Ill   Health is the real wealth. But health and disease are among the most complicated issues in our life. We have to deal with this issue in our life more often. The most important thing to know is that why we fall ill? It has been rightly said prevention is better than cure. The various organ systems in our body work smoothly to keep us healthy.   Health and Its Failure Health is an idea of being well. A good health allows us to work well physically, mentally and socially. A good health enables us to cope up with the social, mental and physical pressure without any difficulty. To keep ourselves fit and healthy we must take a balanced diet, regular exercise and cleanliness in and around us. If we do not follow the above mentioned points then we more...

Natural Resources   Our earth is a unique planet. It supports all forms of life. To support all these forms of life, the nature has endowed this planet with vast resources such as land, air, water, atmosphere, minerals, etc. All these resources are divided into two components, biotic and abiotic. Biotic components constitute all the living things whereas abiotic components constitute all the non-living things.   Abiotic Components Abiotic components consist of air, water, soil, land, weather, climate, etc. These all components are very vital to support all forms of life on this planet.   Air Air is a mixture of many gases such as nitrogen, oxygen, carbon, water vapour, etc. Air is one of the most important factors that supports life on this planet. Our atmosphere constitutes the air. The sunlight is filtered by this atmosphere so that no harmful rays can reach more...

Improvement in Food Resources   Improvement in Food Resources Food is our basic need. From food we derive energy to do all activities. In the last few decades, the population of our country has increased manifold. To provide the food security to this growing population is really a onerous task. It is necessary that there should be an improvement in food resources so that we can provide the food security to our people. Our government has made efforts to meet the food demand by increasing food production. The efforts have brought successes up to a certain extent. The green revolution has increased the production of food grains manifold. The white revolution, has led to better and more efficient use as well as availability of milk. The above mentioned revolutions have led to the extensive use of our resources that cause imbalances. We need to more...

Verbal and Non-verbal Reasoning   Reasoning and logic skills are an integral part of a wide range of subjects of mathematics. These skills are very useful in our daily lives. In this chapter we will solve problems related to verbal and non-verbal reasoning.   Odd-One Out Types of Problems In these types of problems, letters of the alphabet are classified into a group by applying a particular rule or pattern.  

• Example:

Choose the group of letters which is different from the others: BEI, MPT, RVZ, LOS (a) BEI                         (b) MPT (c) RV                          (d) LOS (e) None of these   Answer (c) Explanation: \[B\underrightarrow{+3}\,E\underrightarrow{+4}\,I,\,\,M\underrightarrow{+3}\,P\underrightarrow{+4}\,T,\,\,R\underrightarrow{+4}\,V\underrightarrow{+4}\,Z,\,\,L\underrightarrow{+3}\,O\underrightarrow{+4}\,S\] Clearly, RVZ is different from others.   Problems Related to Missing Number in the Series In these types of problems, we have to find the missing number of the given series, where the given more...