Friction Class 8 Extra Questions and Answers

These AP 8th Class Physics Important Questions and 2nd Lesson Friction Class 8 Extra Questions will help students prepare well for the exams.

Class 8 Science Friction Extra Questions

Friction Class 8 Important Questions

Question 1.
What is frictional force ?
Answer:
The force which opposes the relative motion between two surfaces in contact is called frictional force.

Question 2.
What is static friction ?
Answer:
Static friction is the friction which comes into play when surfaces of objects are at rest relative to each other.

Question 3.
What is sliding friction ?
Answer:
Sliding friction is the friction which comes into play when an object is sliding over another.

Question 4.
What is rolling friction ?
Answer:
When one body rolls over the surface of the other body the friction offered is called rolling friction.

Question 5.
Write the order of friction ?
Answer:
Static friction > Sliding friction > Rolling friction.

Question 6.
What are lubricants ?
Answer:
The substances which reduce friction are called lubricants.

Question 7.
What is drag ?
Answer:
The frictional force exerted by fluids is called drag.

Question 8.
What are the factors which influence friction ?
Answer:
The factors which influence friction are :

1. Nature of surface
2. Normal force

Question 9.
If the friction was! absent can you light a matchstick ?
Answer:
No, to light a matchstick it is to be rubbed against the rough surface of a match box.

Question 10.
What are factors on which frictional force of an object in a fluid depends on ?
Answer:
The frictional force of an object in a fluid depends on its speed with respect to fluid and on the shape of the object and nature of the fluid.

Question 11.
Why do we use grease between moving parts of motor vehicles ?
Answer:
To reduce friction and increases the efficiency of motor vehicles.

Question 12.
What is effect of roughness on friction ?
Answer:
As the roughness of surface increases frictional force increases.

Question 13.
Why do Gymnasts apply some coarse substance on their hands ?
Answer:
Gymnasts apply some coarse substance on their hands to increase friction for better grip.

Question 14.
What is the effect of area of contact on frictional force ?
Answer:
Frictional force is independent of area of contact.

Question 15.
Why do we need to change the tyres when its threading is worn out ?
Answer:
If we does not change the tyre, then the frictional force decreases due to threading worn out tyre thereby the vehicle may skid.

Question 16.
Why birds and fishes have special shapes ?
Answer:
Birds and fishes have to move about in fluids all the time. So they have special shapes which would make them not to lose much energy in overcoming friction.

Question 17.
Why shape of aeroplane is similar to bird ?
Answer:
The shape of birds are useful in reducing the fluid friction. So aeroplane shape was made similar to bird in order to reduce fluid friction.

Question 18.
What are frictional forces produced between two bodies ?
Answer:
The frictional forces produced between two bodies are :

1. Sliding friction
2. Static friction

Question 19.
Why the sole of shoes is grooved ?
Answer:
The sole of shoes is grooved to provide shoes better grip on the floor to move safely.

Question 20.
Vehicle tyres are threaded why ?
Answer:
To provide better grip on the floor, the tyres are threaded.

Question 21.
Is the friction same for all the surfaces ?
Answer:
No, the friction depends on the nature of surface in contact.

Friction Extra Questions

Question 1.
What ways do you suggest to reduce friction ?
Answer:
Ways of reducing friction :
a) Polishing: Decreasing irregularities of surface (or) smoothening the surface.
b) Lubricants: Using lubricants which will decrease the friction.
c) Ball bearing : Using ball bearing in machinery.
d) Steam lining : Automobiles and aeroplanes are steam lined to reduce the friction due to air.

Question 2.
Give examples of practical applications of static friction.
Answer:
The objects unable to move on their own is due to static friction surfaces of object. The practical application of static friction :

1. Construction of buildings.
2. Fixing nail in the wall.
3. We can write with pen or pencil due to static friction between finger and pen or pencil.
4. We will not able to hold appliances such as hammer.

Question 3.
Explain how does lubrication reduce friction.
Answer:
When oil, grease or any other lubricants are applied between the moving parts of a machine, ai thin layer formed between the moving surfaces. So they do not directly rub against each other which will avoid the interlocking of irregularities. Thus, lubrication reduce the friction.

Question 4.
Explain why sliding friction is less than static friction.
Answer:
When an object starts sliding, the contact points on its surface do not get enough time to lock into the contact points on the floor. So the sliding friction is slightly less than the static friction.

Question 5.
What purposes are served by using bearings in machines ? Explain with daily life
examples.
Answer:
Ball bearings are used to reduce friction between rotating shafts of machine tools.
i) Ball bearings are used in fans.
ii) Ball bearings are also used in machines.

Question 6.
Give few examples for sliding friction.
Answer:

1. The trolley moves on the floor.
2. The marbles or any spherical objects slide on the ground or floor when thrown.
3. The tyres make sliding movement on roads which moves the vehicles.

Question 7.
Describe some examples where heat is produced due to friction.
Answer:

1. When we rub our hands together vigorously for few minutes we feel heat due to friction.
2. When we strike a matchstick, against rough surface, it catches fire due to friction.

Question 8.
Why heavier box apply more frictional force than lighter box ?
Answer:

1. We know that the force of friction is increased if the two surfaces are pressed harder.
2. A heavier box presses the ground harder to heavier box apply more frictional force.

Question 9.
Why it is easy to move an object in motion when compared with object at rest ?
Answer:

1. When the box start moving, the contact points on its surface, do not get enough time to lock into the contact point of floor.
2. So it is easy to move the box which already started to move.

Question 10.
What is the function of ridges on your palm and bottom of your feet ?
Answer:
Ridges of our palm help us to make firm grip whenever we hold by our hands – Ridges of the bottom of our feet help us to walk freely and we do not slip because of these.

Question 11.
Describe some examples where we have to increase friction.
Answer:

1. We will increase friction by using brake pads in the brake system of bicycles and automobiles.
2. Kabadi players rub their hands with the soil for an easy grip of their opponents.
3. Gymnasts apply some coarse substances on their hands to increase friction for better grip.

Question 12.
Why do we slip when we step on a banana peel ?
Answer:
As we step on a banana peel, there is no grip between our foot and the banana peel due to very less friction. So, we slip accidentally.

Question 13.
Why is it difficult to walk on a smooth and wet floor ?
Answer:
Due to very less friction on wet and smooth floors, our foot cannot make exact grip with the floor. Thus, it is very difficult for us to walk on these floors.

Question 14.
Can we reduce friction to zero by polishing surfaces or using large amount of lubricants ?
Answer:
No, friction can never be entirely eliminated. No surface is perfectly smooth. Some irregularities are always there.

Question 15.
How a child can pull a heavy luggage fitted with rollers easily ?
Answer:
The roller provides rolling friction instead of sliding the luggage. Since, the rolling friction is very less than the sliding one. Hence, even a child can pull such pieces of luggage easily.

Question 16.
Give a scientific explanation for the following.
a) A door hinge stops squeaking when oiled.
b) Rubber mats are placed on bathroom floors.
Answer:
a) i) When we oiled a door hinge, the friction between hinge and door will be reduced.
ii) So a door hinge stops squeaking when oiled.

b) i) Due to very less friction on wet floors, our foot cannot make exact grip with the
floor.
ii) So, to increase the friction between our foot and wet floor.
iii) Rubber mats are used to do that work.
iv) So, rubber mats are placed on bathroom floors.

Extra Questions of Friction Class 8

Question 1.
Friction is an evil master and good servant to man. Describe.
Answer:
Friction is the obstruction force acting in the opposite direction of the exerted force. It brings the following bad or evil impacts on the bodies.
i) Over heating and wearing out of moving parts in all machinery
ii) Loss of efforts.
In this way it is bad or evil master to man. But. without friction the moving of vehicles on the roads, walking, running, sitting, standing, etc. of us are not possible.

We are able to write with pen or pencil on the papers or walls or any surface is only due to the influence of friction. In this way it is good servant.

Question 2.
What would happen if there were no force of friction ? Imagine and describe in your own words.
Answer:

1. If there were no friction, many problems could have been arisen, as one will not able to walk if they were no friction at all.
2. One cannot write with pen or pencil.
3. One cannot write on blackboard with a chalk.
4. If any object just started moving, ic would never stop.
5. Had there been no friction between the tyres of the automobiles and the road, they cannot be started or stopped or turned to change the direction of motion.
6. One cannot fix the nail in the wall or tie a knot.
7. Without friction no buildings can be constructed.

Question 3.
Scientists designed the shape of an aeroplane using the technique of reducing fluid friction by observing birds shape. How would you appreciate ?
Answer:

1. Objects move through fluids, they have to overcome friction acting on them.
2. Birds and fishes have to move about in fluids all the time.
3. Their bodies must have evolved to shapes which would make them not to lose much energy in overcoming friction.
4. So aeroplanes designed in a special shape to overcome friction without loosing much energy.
   Hence appreciate the idea of scientists to overcome fluid friction by designing shape of aeroplane.