Ncert – class 8- science – Chapter 9: Friction2 Welcome to your Ncert - class 8- science - Chapter 9: Friction2 1. A ball is rolled on four surfaces:a) marble floor, b) on sand, c) on cloth, d) on wood.The force of friction acting on the ball on these different surfaces in descending order will be: a > b > c > d d > b > a > c b > c > d > a c > b > d > a None 2. 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 different surfaces in increasing order will be Wet marble floor, dry marble floor, towel, newspaper Newspaper, towel, dry marble floor, wet marble floor Towel, newspaper, dry marble floor, wet marble floor Wet marble floor, dry marble floor, newspaper and towel. None 3. What measures are taken to reduce fluid friction in aeroplanes? Metals are choosen in a way to make the aeroplane lighter with smoother surface Optimum speed is maintained with respect to the air Streamlined body inspired by birds All of the above None 4. Friction can be increased by increasing: Roughness of the surface Lubricating the surface Grease on the surface Smoothness of the surface None 5. When two surfaces are coated with lubricant, then they will: slide upon each other roll upon each other stick to each other jump on each other None 6. When a body is moving on a surface, the force of friction is called Limiting friction Static friction Rolling friction Kinetic friction None 7. Boats and aeroplanes are ................. so as to reduce fluid friction.fill in the blank. large streamlined broader bigger None 8. Unevenness in the surfaces of the moving body and the surface on which it moves causes: centripetal force frictional force gravitational force centrifugal force None 9. Why are efforts made to reduce friction Both A and B Overcoming friction is a time consuming process. Energy is lost in overcoming friction. None of the above None 10. If we drop a cup of water on a plate and a cup of oil on another plate, water is seen to spread faster along diameter. This is an example related to: rolling friction static friction sliding friction fluid friction None 11. When two surfaces are coated with lubricant, then they will: slide upon each other stick to each other jump on each other roll upon each other None 12. Frictional force increases when surfaces in contact are made very smooth, because of Increase in area Molecular force Decrease in irregularities Decrease in surface area None 13. A car will skid more on a wet road than on a dry road and the car tyres there is more: friction gravity heat lubricant None 14. Match the followingList IList II1. Streamlined body structurea. Less no. of irregularities2. Pressing two objects harder against each otherb. Lubricant3. Greasec.Increase friction 4. Smooth surfaced. Decrease friction 1-d, 2-c, 3-b, 4-a 1-a, 2-b, 3-c, 4-d 1-a, 2-d, 3-b, 4-c 1-d, 2-c, 3-a, 4-b None 15. After an aeroplane completes a voyage, its muzzle feels warmer than the middle and back portion of the main body. This is because: none of these the muzzle suffers less air friction the muzzle suffers zero air friction the muzzle tears apart the air layers and suffers more air friction None Time's up Please Share This Share this content Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Leave a Reply Cancel replyCommentEnter your name or username to commentEnter your email address to commentEnter your website URL (optional) Save my name, email, and website in this browser for the next time I comment.
