Ncert – class 8- science – Chapter 9: Friction2 Welcome to your Ncert - class 8- science - Chapter 9: Friction2 1. 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 none of these the muzzle suffers zero air friction the muzzle tears apart the air layers and suffers more air friction None 2. When two surfaces are coated with lubricant, then they will: stick to each other slide upon each other roll upon each other jump on each other None 3. Match the following List I List II 1. Streamlined body structure a. Less no. of irregularities 2. Pressing two objects harder against each other b. Lubricant 3. Grease c.Increase friction 4. Smooth surface d. Decrease friction 1-a, 2-d, 3-b, 4-c 1-a, 2-b, 3-c, 4-d 1-d, 2-c, 3-b, 4-a 1-d, 2-c, 3-a, 4-b None 4. Frictional force increases when surfaces in contact are made very smooth, because of Decrease in surface area Increase in area Decrease in irregularities Molecular force None 5. Unevenness in the surfaces of the moving body and the surface on which it moves causes: gravitational force centripetal force centrifugal force frictional force None 6. When two surfaces are coated with lubricant, then they will: jump on each other roll upon each other stick to each other slide upon each other None 7. Boats and aeroplanes are ................. so as to reduce fluid friction.fill in the blank. streamlined large bigger broader None 8. 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, newspaper and towel. Newspaper, towel, dry marble floor, wet marble floor Towel, newspaper, dry marble floor, wet marble floor Wet marble floor, dry marble floor, towel, newspaper None 9. A car will skid more on a wet road than on a dry road and the car tyres there is more: friction gravity lubricant heat None 10. 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: d > b > a > c c > b > d > a a > b > c > d b > c > d > a None 11. 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 sliding friction fluid friction static friction None 12. Friction can be increased by increasing: Grease on the surface Roughness of the surface Smoothness of the surface Lubricating the surface None 13. 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 14. What measures are taken to reduce fluid friction in aeroplanes? Streamlined body inspired by birds Optimum speed is maintained with respect to the air All of the above Metals are choosen in a way to make the aeroplane lighter with smoother surface None 15. When a body is moving on a surface, the force of friction is called Rolling friction Kinetic friction Static friction Limiting 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 comment Enter your email address to comment Enter your website URL (optional) Save my name, email, and website in this browser for the next time I comment.
