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NCERT Solutions for Class 8 Science Chapter 9 - Friction

NCERT TEXTBOOK QUESTIONS SOLVED
 

Q. 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.
Ans.
(a) relative motion (b) nature
(c) heat (d) reduces (e) less.
 

Q. 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
Ans.
(c) Static, sliding, rolling.
 

Q. 3. Alida runs her toy car on a 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, 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.
Ans.
(a) wet marble floor, dry marble floor, newspaper, towel.
 

Q. 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.
Ans.
The book moves downwards. The frictional force is acting opposite to the movement of book. So it acts upwards.

NCERT Solutions for Class 8 Science Chapter 9 - Friction


Q. 5. 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?
Ans.
The layer of soap makes floor smooth due to which the friction is reduced and the foot cannot make a proper grip on the floor. Therefore, it is difficult to walk on a soapy floor and we start to slip on the floor.
 

Q. 6. Explain why sportsmen use shoes with spikes.
Ans.
Sportsmen use shoes with spike to increase the friction between shoes and the surface. The shoes with spike do not slip while they run or play.
 

Q. 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?
Ans.
The heavy object will be pressed hard against the opposite surface and produces more friction. So Seema will have to apply a larger force due to more friction.


Q. 8. Explain why sliding friction is less than static friction.
Ans.
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.
 

Q. 9. Give examples to show that friction is both a friend and a foe.
Ans.
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.
 

Q . 10. Explain why objects moving in fluids must have special shapes.
Ans.
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.

The document NCERT Solutions for Class 8 Science Chapter 9 - Friction is a part of Class 8 category.
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FAQs on NCERT Solutions for Class 8 Science Chapter 9 - Friction

1. What is friction and how does it affect the motion of objects?
Ans. Friction is a force that opposes the relative motion between two surfaces in contact. It acts in the opposite direction of motion and can either slow down or stop the motion of an object. Friction also plays a crucial role in enabling the grip between objects and preventing them from slipping or sliding.
2. What are the different types of friction?
Ans. There are mainly four types of friction: static friction, sliding friction, rolling friction, and fluid friction. - Static friction occurs when there is no relative motion between two surfaces, and it prevents the object from starting to move. - Sliding friction comes into play when two surfaces are in motion relative to each other. - Rolling friction occurs when an object rolls over a surface, like a ball rolling on the ground. - Fluid friction is the resistance experienced by an object moving through a fluid, such as air or water.
3. How is friction helpful in our daily lives?
Ans. Friction plays a vital role in our daily lives in various ways: - It helps us to walk or run by providing grip between our feet and the ground. - It allows us to write with a pen or pencil by creating enough friction between the tip and the paper. - It enables the brakes of vehicles to work effectively by creating friction between the brake pads and the wheels. - It helps us to hold objects firmly, like holding a cup or a book, by creating friction between our hands and the object's surface.
4. What factors affect the amount of friction between two surfaces?
Ans. The amount of friction between two surfaces is influenced by several factors: - Nature of surfaces: Different materials have different textures, which affect the friction between them. - Force pressing the surfaces: Increasing the force pressing the surfaces together increases the friction. - Roughness of surfaces: Rougher surfaces tend to have more friction compared to smoother surfaces. - Lubrication: Adding a lubricant, such as oil or grease, between two surfaces reduces friction.
5. How can we reduce friction between two surfaces?
Ans. Friction between two surfaces can be reduced by: - Using lubricants: Applying oil, grease, or other lubricants between the surfaces reduces friction. - Smoothing the surfaces: Making the surfaces smoother, either by polishing or using smoother materials, reduces friction. - Using ball bearings or rollers: Employing ball bearings or rollers between two surfaces minimizes friction. - Reducing the force pressing the surfaces: Decreasing the force between the surfaces reduces friction.
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