Monday, April 27, 2015

Learnwell science class 8 chapter force and pressure n Friction

High order thinking skill [HOTS Questions]

Learnwell science class 8

1. Why are women advised not to wear high heeled shoes?

Ans: High heeled shoes do not distribute weight of body over the surface of and therefore women may fall on the ground due to less grips on ground. This is why women are advised not to wear high heeled shoes.

2. It is more difficult to pull boat on the beach than on the water?

Ans: Liquid and gases exert lesser friction as compared to solid surfaces. Therefore, boat on the beach experience more friction than on the water. Thus, it is more difficult to pull boat on the beach than on the water.

3. How are you able to drink juice using a straw?

Ans: When we suck air from straw the air pressure in the straw decreases that is enough to pull the juice. Air pressure pull the juice to move up inside the straw into our mouth .

4. Why is the tip of sewing needle sharp?

Ans: The sharp tip of sewing needle sharp distributes force over less are so that more pressure created on the clothes. This makes work with needle easier.

5. Why are powder sprinkled on the carom board before playing?
Ans: Powder sprinkled on the carom board before playing to reduce friction between coins and surface of carom board.

6. Why does a woman apply soap solution on their hand to put on bangles?
Ans: A woman apply soap solution on their hand to reduce friction so that it became easier to put on bangles .

7. Does the shoes having spikes on their sole help in making better grip on ice?
Ans: Yes, spikes increase friction and help to have better grip on ice.

8. Will a match stick catch fire when it is rubbed against cemented wall?

Ans: Yes. A match stick catches fire when it is rubbed against cemented wall because force of friction raises the temperature of match stick head.

9. What would happen if there is no friction?

Ans: Friction is the force that opposes the motion of every object. So if there is no friction then, there would be nothing to stop a moving object, and it would continue to move forever

10. Machine parts are oiled occasionally?

Ans: Lubricant like oil and grease form layer between the two moving surfaces so that they cannot directly rub each other. This make the movement smoother.

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Sunday, April 19, 2015

Matter in our surrounding solved questions class9 Step-01

Matter in our surrounding solved questions

Q. 1. What is a matter?

Answer: Anything that occupies space and has mass is called a matter. For example:- Chalk, Milk, Sugar etc.

Q. 2. Sodium chloride and sugar have same appearance. Are they same or different?

Answer: They have different physical and chemical properties. So, they are different

Q. 3. All substances around us are alike. How?

Answer: All substances can occupy space and have weight.

Q. 4. How can we say that air is a matter?

Answer: Air occupies space and have weight. Hence air is a matter.

Q. 5. State the characteristics of matter?

Matter has mass, weight and occupies space.

Q. 6. What are the intensive properties of matter?

Answer: Density, colour, melting point, boiling point, refractive index etc. are the intensive properties of matter as it does not depend upon the amount of matter contained in it

Q. 7. What are the extensive properties of matter?

Answer: The properties which depends upon the amount of matter contained in a substance is called extensive  properties of matter. For example mass, weight, volume, energy etc.

Q. 8. State the characteristics of particles of matter.


(i) There is enough space between the particles of matter.

(ii) The particles of matter are continuously moving about their mean position.

(iii) The particles of matter attract each other.

Q. 9. What is the effect of temperature on a matter?

Answer: Particles of matter posses kinetic energy. As the temperature rises, kinetic energy increases.

Q. 10. The smell of hot sizzling food reaches us several metres away. Why?

Answer: As the rate of diffusion increases with the increase in temperature.

Q. 11. What is diffusion?

Answer: When two gases are mixed, their molecules mix with each other due to their speed and random  motion. This phenomenon is known as diffusion

Q. 12. If a bottle of perfume is opened in one corner of a room, it immediately spreads throughout the room. Why?

Answer: The molecules of a gas are free to move in a chaotic motion at a greater speed throughout the vessel  in which it is contained. When the bottle of perfume is opened in one corner of the room, the molecules of perfume move at random motion in all direction and mix with the molecules of air and  reaches us

Q. 13. Name the three states of matter with examples.

Answer: The three states of matter are:

(i) Solid: - A solid has definite shape and volume.Example – wood, metal, rubber.

(ii) Liquid: - A liquid has definite volume and its shape is the shape of the container.
Example  water, oil, petrol.

(iii) Gas: – A gas has neither a definite volume nor a definite shape.        
Example – air, hydrogen, oxygen.

Q. 14. State the characteristics of solids.

Answer: Solids are rigid. The molecules of solids are packed closely and remain fixed at their position. The  molecules of solids are packed closely and remain fixed at their position. The force of attraction  between the molecules are very strong and hence they resist any change in their shape or volume.

Q. 15. What are the characteristics of liquids?

Answer: Liquids have definite volume but not a definite shape. They take the shape of a container in which  they are stored. The molecules have weaker force of attraction than solids, and hence can flow easily.

Q. 16. What are the characteristics of gases?

Answer: Gases have neither definite volume nor definite shape. The molecules have very weak force of  attraction and low density. They can be compressed to liquid state and flow in any direction.

Q. 17. What are fluids?

Answer: Substances having tendency to flow are called fluids. Liquids and gases are fluids.

Q. 18. Give one similarity between a liquid and a gas and one dissimilarity.


Similarity: - Both liquids and gases are fluids and they take the shape of the container.

Dissimilarity: - A gas can be compressed easily to a desired volume. A liquid can not be compressed easily. A small volume of gas occupies the whole space of the container. But the volume of liquid is  fixed. A large volume of gas can be stored in a container of very small volume.

Q. 20. What property of gas is utilized when natural gas is supplied for vehicles.

Answer: High comprehensibility of gas is utilized and compressed it for supply for the vehicles in the name of  CNG.

Q. 21. What are ‘intermolecular forces’? How are these related to the three states of matter ?

Answer:  The force operating between the atoms or molecules of a matter is called intermolecular force. The  intermolecular force in solid are strong. This keeps the constituent particles very close to each other. 

Due to this solids are rigid and incompressible. This also give ordered arrangement of the particles 
giving regular geometrical shape to the solid.

In liquid, inter molecular force is weak to give definite shape.

In gas, intermolecular force is negligible and so its constituents particles are free to move and occupy 
the available space.

Q. 22. Separate the following substances in groups of high and low intermolecular force:Ice, sulphur 
vapour, nitrogen, sugar, copper, air, salt, plastic.


High intermolecular forces :-    Ice, sugar, copper, salt, plastic

Low intermolecular forces :-     Sulphur vapour, nitrogen, air

Q. 23. Which of the following substances you expect strongest and in which weakest intermolecular 
force:  Water, alcohol, sugar, sodium chloride, carbon dioxide.


Sodium chloride – Strongest

Carbon dioxide – Weakest

Q. 24. Why are gases compressible but liquids not ?

The molecules of a gas are separated very far and there is a lot of empty space between them. Hence 
gases can be compressed easily. In liquids molecules are closer to each other and can be brought 
further closer only under very high pressure.

Q. 25. Compare the process of boiling and vaporization.

(i) It is a process of changing liquid sinto vapour.   
(i) It is a process of changing liquids   into vapour. 
(ii) Molecules of liquids escape from all parts of the liquids into atmosphere.
Molecules of liquids escape from upper surface of the liquid into    atmosphere.   
(iii) It is a fast process.
(iii) It is a slow process.    
(iv) It takes place only at a fixed  temperature called boiling point.
(iv) It takes place at all temperature, even at melting point.
(v) In boiling, the vapour pressure of liquids is equal to the atmospheric
(v) In evaporation the vapour pressure of liquid is less than the atmospheric  

Matter in our surrounding solved questions class9      Step-02 Read_Download

Thursday, April 9, 2015

Class7 Nutrition in Animals Science

Nutrition in animals  Holozoic nutrition:
It is a method of nutrition that involves the ingestion of liquid or solid organic material.

It involves different steps namely, ingestion, digestion, absorption, assimilation and egestion.

Human beings exhibit holozoic mode of nutrition involving five basic steps.
Digestion is the process by which complex food is broken down into simple absorbable form.

Digestion of food starts from mouth and ends in small intestine

Digestive system is made up of alimentary canal and associated glands.

Digestive system in human beings:
Digestive system in human beings is formed by alimentary canal and digestive glands.

Parts of alimentary canal:
It comprises different parts like mouth, oesophagus, stomach, small intestine and large intestine. It starts with mouth and ends with anus. 

The process of taking in food through mouth is called as ingestion.


Teeth help in the process of mastication. Mastication is the process of mixing chewed food with saliva.

Digestion of food starts in the mouth with the help of salivary amylase present in the saliva.

Salivary amylase is the enzyme which digests starch into glucose for absorption


Pharynx is the common channel for food and air. When we swallow food, a flap-like valve called the epiglottis closes the windpipe. Epiglottis prevents the entry of food particles into respiratory tract.

Oesophagus also called as food pipe helps in conveying the food from buccal cavity to stomach. The oesophagus is also known as the gullet. It is about 25 centimetres long.

Peristaltic movements
Peristaltic movements are the alternate contractions and relaxations of oesophageal wall which bring about movement of food from buccal cavity to the stomach.

Food conveyed to the stomach is called as bolus as it is round in shape.

Stomach is the widest part of the alimentary canal. It is a J-shaped muscular organ divided into three parts namely, cardia, fundus and pylorus regions.

Stomach as a whole can hold at about two litres of food.

Stomach secretes a fluid called as digestive juice called gastric juice .

Gastric juice
It is made up of hydrochloric acid, mucous and enzymes like pepsin and rennin.
Hydrochloric acid kills the bacteria present in the food and softens the molecules of food. 


Mucous protects inner lining of the stomach from the action of hydrochloric acid. 


Digestive enzymes partially digest some nutrients like proteins and fats. Stomach churns the food into a milky paste. This partially digested food is called as chyme. 

Chyme is conveyed to small intestine for further digestion. Chyme is acidic in nature.

Small intestine
Small intestine is made up of three regions namely duodenum, jejunum and ileum. 

• Acidic chyme from the stomach is received by the duodenum for further digestion.
• Duodenum also receives bile form the liver. Bile reduces the acidity of chyme.
• Bile also provides alkaline environment to activate some enzymes which bring about digestion of certain nutrients in the food.
• Duodenum also receives pancreatic secretions which help in the digestion of food.
• Duodenum also secretes some enzymes on its own.
• All these substances bring about digestion of food in the intestine.
• The inner walls of small intestine are thrown into many folds which have millions of small finger like projections called villi.
Villi increase

• Villi increase the surface area for digestion as well as absorption of digested food by eight times. 

Small intestine also helps in the process of absorption and assimilation. 

Large intestine
• Undigested food is sent into large intestine.

Large intestine comprises of colon and rectum. Large intestine receives undigested food from small intestine.
Water from the food is reabsorbed to a great extent in the large intestine.
Semi-solid undigested waste is stored in the rectum for defecation.
Anus is the opening of the alimentary canal to the exterior. This helps in the elimination of faeces by the process of egestion.

Digestive glands: 

These glands are also called as associated glands. These are also considered to be exocrine glands which have ducts to drop their secretions into the target organ directly. The secretions of the digestive glands help in the process of digestion. These glands include salivary glands, gastric glands, intestinal glands, liver and pancreas.

Salivary glands are present inside the buccal cavity. They secrete saliva. Saliva helps in lubrication of food . This saliva plays an important role in breaking down complex components like starch into simple sugars. It brings about partial digestion of starch.

Gastric glands are microscopic glandular cells present in the inner lining of the stomach. Gastric glands secrete gastric juice comprising HCl, pepsin and prorennin. 

Gastric juice helps in the digestion of proteins. Gastric juice helps in emulsification of fats.

Intestinal glands are present in the inner lining of small intestine. These secrete various enzymes which aid in the process of digestion of all the components of food.

Liver is the largest gland in our body. The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder. 

Bile provides an alkaline environment for many enzymes to get active. It also reduces the acidity of chyme. Bile plays an important role in the digestion of fats. 

Bile is sent into duodenum through a narrow tube-like structure called the bile duct. 

Bile breaks the larger fat molecules into tiny droplets, thereby increasing their surface area, which helps in the digestion of fats easily.

Pancreas is the mixed gland. It acts as both endocrine and exocrine gland. The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the lipids into fatty acids and glycerol.

Absorption: The process of allowing simple absorbable nutrients into blood capillaries through surface of the villi is called as absorption. Inner wall of small intestine comprises many finger like projections called as villi. Villi increase the surface area for absorption of food.

Each villus is made up of central structure called as lacteal which mainly absorbs simple fats and transports them into lymphatic system. 

Lacteal is surrounded by a network of fine blood capillaries. Blood capillaries absorb glucose molecules and amino acids and transport them in the blood. Vitamins and minerals get readily absorbed into the blood.


The process of utilisation of absorbed food, such as glucose, amino acids, fatty acids and glycerol is called as assimilation. Energy needed for various activities is obtained from glucose. 

Glucose is broken in the cells in the presence of oxygen to syntheise energy in the form of ATP. 

Amino acids are used for building and repairing body parts. Fatty acids and glycerol are stored in the adipose tissue and under the skin for future use.


It is the process by which undigested food is passed to exterior through an opening called as anus. Rectum stores undigested waste in the form of faeces. Faeces are sent out through anus.

Solved questions Class 7 Science Nutrition in Animals

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Wednesday, April 8, 2015

The language of chemistry class 7 Basic science soled questions

Q. What is chemistry?
Ans: Chemistry is a branch of science in which we study the composition, structure, properties and change of matter.

Q. What is matter?
Ans: Anything that is around us having some mass and occupies space is called matter.

Q. What are the different classifications of matter?
Ans: Matters are classified into element, compound and mixture.

Q. What is element?
Ans: Elements are the purest form of substance (matter) made up of same kinds of particles. The smallest unit of element is an atom. eg. Hydrogen, oxygen, carbon.

Q. What is compound?           

See full post  The language of chemistry class 7 Basic science

Class 07 Basic sciences Chapter the Language of Chemistry
A. Answer these questions

1. What does the formula of a substance tell us?

Answer: Formula of a compound or an element represents the name and number of atoms present in one molecule of that compound or element.

2. What do you mean by valancy of an element?

Answer: The number of electrons that can be donated, accepted or shared by an atom of an element during a chemical reaction is equal to the valency of that element. Thus the combining capacity of an atom is called its valancy.

3. What is a radical?

Answer: A compound radical is a group of two or more elements that acts as a single atom in a chemical reaction.
4. Name two elements having variable valancy. Give the name and formulae of compounds formed byeach of these element.

Answer: Two elements having variable valency and compounds formed by them are as follows:

(i) Copper (Cu):  
(a) Cuprous oxide [Copper (I) oxide] − Cu2O     
 (b) Cupric oxide [Copper(II)oxide] − CuO

(ii) Iron (Fe):  (a) Ferrous oxide [Iron(II)oxide] − FeO                    
(b) Ferric oxide [Iron(III)oxide] − Fe2O3

5. What is balance equations? Why should a  equation be balanced?

Answer: A reaction is in which the number of atoms on the side of the products is equal to the number of atoms on the side of the reactants is called a balanced chemical. This is known as law of the conservation of mass given by Antoine Lavoisier's 1789.  We balance a chemical reaction to represent this fact.

B. Find the vacancies of the underlined element or radicals in the following compound?


Valency of Underlined
Valency of Underlined
Valency of Underlined
Valency of Underlined

C. What are compound radicals? Give examples of a few radicals, along with their valancies. Also mention some compound containing compound radicals. Give the valancies of the part that make up the compound?

Answer: Compound radical is a group of atoms of different elements that behave as an intact unit during a chemical reaction. Atoms in a compound radical do not break apart revealing the individual atoms but remain together forming an intact group of atoms having a valency. This unit behaves just like an atom or a molecule during a reaction.
Some compound radicals with their valencies are given below:

Compound Radical        Valency
OH                               1
SO4                              2
NO3                              1
CO3                              2

Some compounds containing compound radicals:

Compound Radical
Sodium hydroxide
Sulphuric acid
Sodium carbonate
Ammonium sulphate
 Potassium nitrate

D. Complete the following

Answer :

1. A symbol is an abbreviation of the name of an element.
2. A molecule of an element or a compound is represented by its formula.
3. The valencies of the two elements of a binary compound are transposed to obtain its formula.
4. Atoms are neither lost nor gained in a chemical reaction.
E.Choose the correct options
1. Which of the following is the symbol of gold?
C. Au   
2. Which of the following is a divalent radical                                                      
(c) Sulphate                 
3. The vaancy of sulphur in sulphur dioxide                                                       
 (d) 4                
4.How many times greater is the valency of N in NH3 than that of Cl in HCl          
(b) 3
Valency of N in NH3 is 3, whereas the valency of Cl in HCl is 1.  
Hence, the valency of N in NH3 is three times greater than that of Cl in HCl.

F. Match the coloumn

Answer :

Column A
Column B
(a) Helium
(ii) He
(b) Mercury
 (i) Hg
(c) Copper
(v) Cu
(d) Calcium
(vi) Ca
(e) Phosphorus
(iv) P
(f) Lead
(iii) Pb

G. Say true and false

Answer :

1. True. The valency of hydrogen is 1.
2. True. The valency of oxygen is 2.
3. False. Symbol of iron is Fe.
4. True. The symbol of silver is Ag.
5. False. Calcium chloride is CaCl2.
6. True. The valency of both zinc and oxygen is 2. So, zinc oxide is ZnO

H. Write the formula of following compound

Answer :

Calcium oxide
Carbon dioxide
Carbon monoxide
Magnesium oxide
Hydrogen chloride
 H Cl
Sodium chloride
Potassium chloride
Magnesium chloride
Zinc chloride
Nitric acid
Sodium nitrate
Sodium carbonate
Potassium carbonate
Calcium carbonate