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.

.CLASS 8 REVISION WORKSHEET

CELL -STRUCTURE 

Write two examples of prokaryotes.

2.

In which part the  cell chromosomes of a cell are visible?

3.

Write the function of nerve cells.

4.

Expand DNA

5.

State True or False: The basic living unit of an organism is an organ.

1. true2. false

6.

State True or False: Pseudopodia is called false feet in amoeba.

1. true2. false

7.

Write the function of chromosomes.

8.

Write three parts of the cell that are very important for its functioning.

9.

Why is mitochondria called the powerhouse of the cell?

10.

State True or False: Tissue consists of dissimilar cells.

1. true2. false

Worksheets by UrbanPro

Long Answer Questions for class 8

Question 1.
Differentiate between prokaryotic and eukaryotic cells?
Answer

S.No.	Prokaryotic cell	Eukaryotic cell
1	They are primitive and incomplete cells	They are advance and complete cells.
2	Do not have well defined nucleus (nucleiod)	Have well defined nucleus (true nucleus)
3	Membrane bound cell organelles are absent.	Membrane bound cell organelles are present.
4	Bacteria and Mycoplasma are prokaryotic cells.	Animal cells and Plant cells are eukaryotic cells.

Question 2.
Write the functions of different types of plastids?
Answer
Plastids with green�coloured photosynthetic pigment (chlorophyll) are called chloroplasts. They are also called kitchen of a plant cell.
Leucoplasts are colourless plastids and store food in the form of starch and fat.
Plastids with pigments other than green are called chromoplasts. These plastids give the flowers and fruits their bright colours, which attracts insects and animals for pollination.

Question 3.
Name any two types of cells that are capable of changing their shape. How does this feature help them in their functions?
Answer
The two types of cells that are capable of changing their shape are:
(i) White blood cells (WBCs): The white blood cells present in our blood can change their shape. This helps them to kill germs by engulfing them.
(ii) Amoeba: Amoeba can change its shape with the help of pseudopodia that are projections of its body. The pseudopodia help the Amoeba to capture its food and move from one place to another.

Question 5.
What are the lower levels of organization in multicellular organisms? Are these levels present in unicellular organisms? Answer
In a multicellular organism, the lower levels of organization are as follows: Cells → Tissues → Organs → Organ systems → Organism
No, these levels are not present in unicellular organisms because unicellular organism consists of single cell.

Practice questions:

1. What is cell?
2. State the key features of cell theory?
3. Who saw cells first and when?
4. Why is a cell membrane important to a cell?
5. Name two organelles present in plant cell but not present in an animal cell?
6. What do you mean by protoplasm?
7. What are the building blocks of life? Why are they so called?
8. Differentiate between unicellular and multicellular organisms?
9. What is cell division? Why it is necessary?
10. Write the functions of nucleus and chromosome?
11. What is function of ribosomes?
12. What are the differences between animal cell and plant cell?
13. Why are cells of different shapes and sizes? Give suitable example?
14. Why is lysosomes known as suicidal bag of the cell?
15. Draw a diagram of animal cell and plant cell?

16. Name the stains used in the preparation of animal  and plant cell?