Ncert – class 8- science – Chapter 9: Friction2 Welcome to your Ncert - class 8- science - Chapter 9: Friction2 1. Unevenness in the surfaces of the moving body and the surface on which it moves causes: frictional force centrifugal force centripetal force gravitational force None 2. What measures are taken to reduce fluid friction in aeroplanes? Metals are choosen in a way to make the aeroplane lighter with smoother surface Streamlined body inspired by birds All of the above Optimum speed is maintained with respect to the air None 3. 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 4. Boats and aeroplanes are ................. so as to reduce fluid friction.fill in the blank. large broader bigger streamlined None 5. When two surfaces are coated with lubricant, then they will: slide upon each other jump on each other roll upon each other stick to each other None 6. Friction can be increased by increasing: Roughness of the surface Smoothness of the surface Lubricating the surface Grease on the surface None 7. A car will skid more on a wet road than on a dry road and the car tyres there is more: gravity lubricant heat friction None 8. When a body is moving on a surface, the force of friction is called Static friction Kinetic friction Limiting friction Rolling friction None 9. 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-a, 2-d, 3-b, 4-c 1-d, 2-c, 3-b, 4-a 1-d, 2-c, 3-a, 4-b 1-a, 2-b, 3-c, 4-d None 10. After an aeroplane completes a voyage, its muzzle feels warmer than the middle and back portion of the main body. This is because: the muzzle suffers less air friction the muzzle tears apart the air layers and suffers more air friction the muzzle suffers zero air friction none of these None 11. 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 Wet marble floor, dry marble floor, newspaper and towel. Towel, newspaper, dry marble floor, wet marble floor None 12. 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: c > b > d > a a > b > c > d b > c > d > a d > b > a > c None 13. Why are efforts made to reduce friction None of the above Energy is lost in overcoming friction. Both A and B Overcoming friction is a time consuming process. None 14. 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: sliding friction fluid friction static friction rolling friction None 15. Frictional force increases when surfaces in contact are made very smooth, because of Increase in area Decrease in surface area Molecular force Decrease in irregularities 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.
