1 . 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
2 . Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Explain with a diagram
3. 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?
Class 8
Answers
Answer:
(c) static, sliding, rolling
Arranging the forces in decreasing order goes like static > sliding > rolling. This means that static force is the huger force. A static force keeps an object at rest. Here, the friction experienced by any individual to move that object is known as static friction. (Example- A book kept at rest.) While the sliding force is relatively smaller than the static force. When a body slides over another, the force acting is called sliding force. And the friction that acts at this time is known as Sliding friction. (Example- When a book slides over another.) And the smaller force is the rolling force. When a body rolls over another, the force present is known as rolling force. And the force opposing this motion is known as rolling friction. (Example- a ball rolling over a book or a wood plank.)
It can be experimentally proved that the rolling force is smaller than the sliding force, so it's easier to roll an object over another rather than making it slide.
2. When a book slides over the desk, a frictional force acting between the book and the table tries to oppose this motion. Since the book doesn't get enough time to get interlocked with the small irregularities present on the surface of the table, it keeps on rolling down and down. (Diagram attached)
3. Suppose we spill a bucket of soapy water on the ground, it would become difficult for us to walk due to a decrease in frictional force. It is irregularities present in the floor which gets interlocked with our soles of shoes, slipper or feet and helps us to walk easily. On spilling soapy water, these uneven irregularities get filled with water and due to the extreme minimised force of friction it becomes difficult for us to walk and we may fall.
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