Extra questions of lesson Reproduction

CLASS 9 REVISION

CLASS 8 REVISION WORKSHEETS

CLASS 8

CLASS 7 REVISION PAPERS

CLASS 10 PRACTICAL-SAPONIFICATION

Class9A Atoms and m

page2

page3

page1

Page 4

CLASS 8 Age of Adolescence

class 8
GLANDS IN HUMAN BEINGS

Chemistry Holiday HW
Page 3 of lesson notes

 Page 2of lesson notes

 Pg4 of lesson notes

 Page1 of lesson notes

 Worksheet

class 8 revision worksheet on friction
1.   Complete the sentence. Friction always ____________

       a. helps the motion

       b. opposes the motion

       c. both of these

       d. none of these

2.   Which one of these characteristics does a smooth surface has?

       a. Less frictional force

       b. More frictional force

       c. Sometimes less and sometimes more force

       d. All of above

3.   Friction is a __________

       a. Contact force

       b. Non-contact force

       c. Magnetic force

       d. None of these

4.   What kind of substances are known as lubricants

       a. Increase friction

       b. Decrease friction

       c. Increase or decrease friction

       d. None of these

5.   Fluid are____

       a. Gases

       b. Liquids

       c. Gases and liquids both

       d. None of these

6.   On what force of friction depends?

       a. Smoothness of surface

       b. Roughness of surface

       c. Inclination of surface

       d. Al of above

7.   Friction is a /an_______

       a. Evil

       b. Foe

       c. Both (a) and (b)

       d. None

8.   Lubricants ________

       a. Increase friction

       b. Reduce friction

       c. Both (a) and (b)

       d. None

9.   Rolling friction is smaller than?

       a. Sliding friction

       b. Static friction

       c. Fluid friction

       d. All of the above

10.   The shape of the airplane is like a

        a. Bird

        b. Car

        c. Dog

        d. All

Answers

1.    B

2.    A

3.    A

4.    B

5.    C

6.    D

7.    C

8.    B

9.    D

10. A

1.   Does friction depend on the nature of objects?

2.   Which type of surface produces more friction?

3.   Which type of surface produces less friction?

4.   Which is less sliding friction or static friction?

5.   Why is it difficult to move on a wet marble floor?

6.   What would happen when an object starts moving if there is no friction?

7.   Give two examples where friction is undesirable?

8.   Our hands become warm when we rub them. Why?

9.   Why do we shape aero planes like that of bird?

10.   Write some methods to reduce friction?

11.   Write various types of friction.

12.   What is a fluid friction? Write the factors on which fluid friction depends.

Chapter 6 - Physical and Chemical Changes - 1

·         Chapter 6 - Physical and Chemical Changes - 1

·         Physical and Chemical Changes – QuestionsPage

Physical and Chemical Changes

Q1. Fill in the blanks.

                           i.        Cutting a log of wood into pieces is a physical change.

                          ii.        Condensation is a physical change.

                         iii.        When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium Carbonate.

                         iv.        Two methods by which rusting of iron can be prevented are painting or greasing and galvanisation.

                         v.        Changes in which only physical properties of a substance change are called physical changes.

                       vi.        A medicine is the end product of a chain of chemical reactions.

Q2. True/False

                           i.        Formation of manure from leaves is a physical change. False

                          ii.        Iron pipes coated with zinc do not get rusted easily. True

                         iii.        Iron and rust are the same substances. False

                         iv.        The chemical name of baking soda is Sodium hydrogencarbonate. True

                          v.        Changes in which new substances are formed are called chemical changes. True

Q3. What type of change is crystallisation?

Ans. It is a physical change.

Q4. What type of change is involved in rusting of iron?

Ans.  Rusting of iron is a chemical change.

Q5. Write one property of stainless steel.

Ans. It does not rust.

Q6. What type of change is formation of manure?

Ans. Formation of manure is a chemical change.

Q7. Which of the two is permanent change chemical change or physical change?

Ans. Chemical change is a permanent change.

Q8. What do you understand by chemical change?

Ans. A change in which one or more new substances are formed is called a chemical change.

Q9. State the conditions necessary for rusting of iron?

Ans. For rusting, the presence of both oxygen and water (or water vapour) is essential.

Q10. What is galvanisation?

Ans. The process of depositing a layer of metal like zinc or chromium on iron is called galvanisation.

Q11. What is added to steel to make it stainless?

Ans. Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese.

Q12. Why formation of manure from leaves is a chemical change?

Ans. Formation of manure from leaves is a chemical change because manure formed has a different composition from leaves.

Q13. Why souring of milk is a chemical change?

Ans. Souring of milk is a chemical change because it results in formation of new substance.

Q14. What is rust?

Ans. If a piece of iron is left in the open for some time, it acquires a film of brownish substance. This substance is called rust.

Q15. What is blue vitriol?

Ans. Crystals of copper sulphate pentahydrate are blue in colour. So, it is commonly known as blue vitriol.

Q16. Name the two methods by which rusting of iron can be prevented.

Ans. Two methods by which rusting of iron can be prevented are by painting or greasing and by galvanizing.

Q17. What happens when baking soda is treated with vinegar?

Ans. Vinegar (Acetic acid) + Baking soda (Sodium hydrogencarbonate) → Carbon dioxide + other substances

Q18. Which technique is better for obtaining sugar from sugar solution?

Ans. Crystallization is considered as a better technique for obtaining sugar from sugar solution.