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