NCERT Solutions Class 8 Science
The NCERT Solutions in English Language for Class 8 Science Chapter – 12 (Friction) has been provided here to help the students in solving the questions from this exercise.
Chapter – 12 (Friction)
1. Fill in the blanks.
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces.
(c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.
Answer –
(a) Friction opposes the motion between the surfaces in contact with each other.
(b) Friction depends on the nature of surfaces.
(c) Friction produces heat.
(d) Sprinkling of powder on the carrom board reduces friction.
(e) Sliding friction is lesser than the static friction.
2. 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
Answer – (c) static, sliding, rolling
3. 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
Answer – (a) wet marble floor, dry marble floor, newspaper and towel.
4. 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.
Answer – When a book slides on the writing desk, a frictional force acts between the book and the surface of the desk. The direction of frictional force on the book is opposite to the direction of its motion and acts in upward direction, as shown in the figure alongside.
5. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer – We are able to walk easily on the ground because of the friction in between the floor and our feet On a soapy floor, since the floor is now more smooth, friction will be less. Due to less friction between the floor and our feet, it will be more difficult for us to walk.
6. Explain why sportsmen use shoes with spikes.
Answer – Sportsmen need to run very fast, so they need more friction between the ground and their shoes. So, they use shoes with spikes because it increases friction with the ground and does not let the player fall or slip.
7. 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?
Answer – It is easier to push a light box because the force applied on the floor is less, hence the friction is less On the other hand, it is difficult to push a heavy box because the force applied on the floor is larger,hence friction is much more. Thus, Seema will have to apply a larger force than Iqbal to push the box.
8. Explain why sliding friction is less than static friction.
Answer – The two sliding objects find less time to get interlocked against each other (objects and irregularities of surface). So they get less friction. Therefore sliding friction is always less than static friction.
9. Give examples to show that friction is both a friend and a foe.
Answer – Examples to show that friction is a friend and a foe:
Friction is a friend:
(i) Friction allows us to grip and catch different objects.
(ii) It helps us to walk comfortably on the surface.
(iii) It helps to minimise the speed or to stop the moving objects.
(iv) It helps us to write on paper or blackboard.
(v) The things do not move from their place due to the friction between the surfaces.
Friction is a foe:
(i) Friction causes wear and tear in objects.
(ii) It causes damage to the parts of machines.
(iii) The machines or tools require regular maintenance due to which a lot of money is wasted.
(iv) It reduces the speed of moving objects, so more force is required.
(v) It does not allow the free movement of objects.
10. Explain why objects moving in fluids must have special shapes.
Answer – The object moving in fluids must have a special shape. This type of shape is called streamlined shape. The streamlined shape helps to overcome the friction between objects and fluids. The objects have pointed fronts with little broader middle portion which gets tapered at the back.
