NCERT solution for class 8 > Science > chapter 12 - Friction

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NCERT solution for class 8  > Science  > chapter 12 -  Friction

Chapter 12 - Friction 

                Exercise 

Q1. Fill in the blanks 

a) Friction opposes the the motion between the surface in the contact with each other .

b) Friction depends on the roughness of surface 

c) Friction produces heat

d) Sprinkling of powder on the carrom board reduce friction.  

e) Sliding friction is lesser than static friction .

Q2. Four children were asked to arrange forces due to rolling status and sliding friction in the decreasing order of their arrangement are given below choose the correct arrangement 

a) rolling, static, sliding 

b) rolling ,sliding ,static 

c) static ,sliding, rolling 

d) sliding ,static, rolling 

Answer- static ,sliding, rolling

Q3. Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor the force of friction acting on the car on the different surface in increasing order will be 

a) wet marble floor ,dry marble floor ,newspaper and towel 

b) newspaper , towel ,dry marble floor , wet marble floor. 

c) towel, newspaper , dry marble floor, wet marble floor 

d) wet marble floor, dry marble floor, towel, newspaper  

Answer- Wet marble floor ,dry marble floor ,newspaper and towel 

Q4. Suppose your writing desk is tilted a little a book kept on it starts sliding down show the direction of frictional force acting on it . 

Answer- Friction force act opposite to the motion of the book

Q5. You spill a bucket of soapy water on a marble floor accidentally would it make it easier or more difficult for you to walk on the floor why?  

Answer- It would difficult to walk on the soapy water falls the floor . It reduces the friction considerable and feet are not able to grip on the floor surface . So it increasing the chances of falling

Q6. Explain why sportsmen use shoes with spikes? 

Answer- Spikes reduces the friction and provide the better grip with the ground so it avoids slipping during playing and running

Q7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor who will have to apply a larger force and why?

Answer- Seema will have apply more force because force is directly proportional to the mass of the object heavier box will put more force on the floor surface while lighter box produce less force

Q8. Explain why sliding friction is less than static friction? 

Answer- When object is in rest condition then the surface of the object is show high Friction than that of the object are in moving the interaction between their surfaces is lower that's why sliding friction is less than static friction

Q9. Give examples to show that friction is both a friend and a foe? 

Answer- Friction acts as a friend 

a) Nails and screws stick to wall surfaces because of friction .

b) We are able to run because of the frictional force between ground and our feet.

Friction acts as a foe 

a) Machines gets heated up because of friction 

b) Shoe soles becomes tear due to friction

Q10. Explain why objects moving in fluids must have special shapes? 

Answer-  Fluids have a special friction that we called fluid friction and to minimise the fluid friction And the body  smoothly move in the fluids  .It has a special shape they may be spherical or streamlined shape with a smooth surface 

Example - aeroplanes jets, raindrop ,fish ,birds etc.



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