Q24. Which type of friction comes into play when a book on cylindrical pencils is moved by pushing?
Q25. Name the device which is attached to heavy luggage (such as a heavy suitcase) to move it easily by pulling.
Q26. Give one example from everyday life where wheels (or rollers) are used to reduce friction.
Q27. Why a bicycle and a motor mechanic use grease between the moving parts of these machines?
Q28. Why are cars, aeroplanes and rockets streamlined?
Q29. What prevents us from slipping every time we take a step forward?
Q30. Why are treads made in the surface of tyres?
Q31. What are fluids? Name two common fluids.
Q32. Why do gymnasts apply a coarse substance to their hands?
Q33. Why is it difficult to climb up an oily or greasy pole?
Q34. Why do tyres of cars wear out gradually?
Q35. What is static friction?
Q36. What is sliding friction?
Q37. What is rolling friction?
Q38. Why is it difficult to walk on a well-polished floor?
Q39. Why is it difficult to walk on a smooth and wet floor?
Q40. Can we reduce friction to zero by polishing surfaces or using large amount of lubricants?
Q41. Which device is used between the hubs and axles of bicycle wheels to reduce friction?
Q42. What happens when you rub your hands vigorously for a few seconds? Why does this happen?
Q43. Explain why sportsmen use shoes with spikes.