14. Why is fine powder sprinkled on the carrom board? 15. Why is it difficult to walk on the wet marble floor? 16. Why does the jar of a mixer become hot when it is run for a few minutes? 17. Name the types of friction. 18. Which force helps us to write on the paper or blackboard? 19. What is a drag? 20. What are fluids? 21.Give some examples having streamlined body. 22.Oil, creams and grease are called lubricants. Why? 23.How can fluid friction be minimised? 24.When does static friction come into play? 25.Can we reduce friction to zero? 26.Why is it easier for the fish to swim in water? 27.What is a spring balance? 28.How does the friction depend on the nature of the surface? 29.What are the two factors on which the force of friction depends? 30.When the two surfaces are pressed harder, friction increases. Explain why? 31.Why is it easier to move the box already in motion than to get it started? or The sliding friction is slightly smaller than the static friction. Explain why? 32.Why are the soles of shoes and tyres of vehicles grooved? 33. We use ball bearings between the hub and axle of ceiling fan and bicycles. Why? 34.Why are lubricants applied between the moving part of a machine?
Answers
Answer:
14. Why is fine powder sprinkled on the carrom board?
Ans- To make the Board smoother.
14.The carom board may sometimes be very rough. Sprinkling powder on a microscopic level, the powder particles offer rolling friction to the striker because of which the striker can be used for smooth and fast play..
15.Friction. ... The water on a wet marble floor fills the microscopic irregularities on the surface and hence present lesser frictional force. It is therefore difficult to move on a wet marble floor..
16.The Jar of a mixer grinder get hot when run for few minutes due to friction & rotation of blades of grinder . during rotation of blade particles collides with wall. As we know that friction produce heat & sound which makes hot the wall of mixer grinder after few minutes of operation...
17.There are two main types of friction, static friction and kinetic friction. Static friction operates between two surfaces that aren't moving relative to each other, while kinetic friction acts between objects in motion...
18.Frictional force helps us to write using chalk on black board......
19.pull (someone or something) along forcefully, roughly, or with difficulty....
20.a substance that has no fixed shape and yields easily to external pressure; a gas or (especially) a liquid.....
21.Fishes have streamlined body so that they have less resistance when swimming in water. Birds have a streamlined body to make their flight easier through air. Snakes have streamlined body to help them move forward...
22.Oil, creams and grease are called lubricants because they are used to reduce friction.....
23.The fluid friction or drag can be reduced are minimised by giving special shape called streamlined shape to the objects which Move through fluids like air or water . ... For example: 1)Cars are built with streamlined body shape to reduce air resistance or drag caused by a air......
24.When the body is in rest or have tendency to move then it has static friction and when the body is in motion, the kinetic friction may oppose or may support the motion depending on the conditions. The direction of frictional forces is opposite of the Applied force on the object..
25. friction force can never be reduced to zero but instead can be reduced to some extent.....
26.
Fish swim by flexing their bodies and tail back and forth. Fish stretch or expand their muscles on one side of their body, while relaxing the muscles on the other side. This motion moves them forward through the water......
Hope it helps.....