Science - Grade 8 (C ...

Q57. Why will a pencil write on a paper, but not on a glass?

 

Q58. When we try to push a very heavy box kept on ground, it does not move at all. Which force is preventing this box to move forward? Where does this force act?

 

Q59. Explain why objects moving in fluids must have special shapes.

 

Q60. Give examples to show that friction is both a friend and a foe.

 

Q61. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.

Choose the correct arrangement.

(a) Rolling, static, sliding

(b) Rolling, sliding, static

(c) Static, sliding, rolling

(d) Sliding, static, rolling

 

Q62. 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:

(a) Wet marble floor, dry marble floor, newspaper and towel.

(b) Newspaper, towel, dry marble floor, wet marble floor.

(c) Towel, newspaper, dry marble floor, wet marble floor.

(d) Wet marble floor, dry marble floor, towel, newspaper.

 

Q63. You spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?

 

Q64. Which is easier to hold in hand: a kulhar (earthen pot) or a glass tumbler? Why?

 

Q65. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

 

Q66. How do rough and smooth surfaces affect friction?

Or

Why do smooth surfaces have less friction?

Or

Why do smooth surfaces have less friction than non-smooth surfaces?

Or

Why does a rough surface have greater friction than a smooth surface?

Or

Friction depends on the nature of two surfaces in contact. Explain.

Or

Is the friction the same for all the surfaces? Does it depend on the smoothness of the surfaces?