Friction / Class-8 / Chapter-12 / New St. Mery English School

1-What is friction ?

Ans:- Friction is the force that generated when two surfaces rub against one another. It is the force which oppose the relative motion between the two surface that are In contact with each other. 

 

 Friction is also called a contact force because it occurs when two surface are in contact and one surface tries to move on other surface.

 

2-How many types of friction ?

There are three types of friction.

1-static friction

2-sliding friction

3-rolling friction

 3-What is static friction?

Ans:- Static friction is the force acting between two surface when they are not moving relative to each other. 

Ex:- 1-A Stationary book on table.

        2-A Tree rooted on ground.

 

 4- What is sliding friction?

Ans:- Sliding friction is the force acting between the two surfaces when one object slides on another object. Sliding friction is slightly smaller than the static friction but larger than the rolling friction.

5- What is rolling friction?

Ans:- Rolling friction is the force acting between the two surfaces when an object rolls over another object.

*Rolling friction is smaller than the static and sliding friction.

6:- What is fluid friction or drag?

Ans:- Fluids like liquids and gases exert a force of friction when an object moves through them. This friction is called fluid friction or drag.

 

7-What is relative motion?

Ans:- Relative motion is the motion of an object With regard to some other moving object. 

 

8-Why friction is also known as contact force?

Ans:-  Friction is also called a contact force because it occurs when two surface are in contact and one surface tries to move on other surface. 

 

9:- What is the reason for the force of friction?

Ans:- No any object is completely smooth. they have tiny bumps on their surfaces. Friction is caused by the intersection of tiny bumps on surfaces as they rub against each other.

 

10:- Write two factors that affecting the friction?

Ans:- The factors that affecting the friction are

 

 1:- friction depends on the nature of the surface. Rough surface has more friction than the smooth surface.

 

2:- Friction also depends on the mass of the object. Heavier object has more friction than lighter object.

 

11:- Write seven advantages of friction.

Ans:- Seven advantages of friction are

 

1:- Friction helps us to walk. Without friction, we would slip and fall.

 

2:- Friction helps us to slow down or stop the moving object. If there were no friction, an object in motion would never stop.

 

3:- Friction between tyres and road helps the vehicles to move on the road.

4:- Friction helps us in writing.

5:- Friction helps us to hold any other objects.

6:- Friction helps us in lighting a matchstick.

7:- Friction holds a nail in a wall.

 12:- Write four disadvantages of friction.

Ans:- Four disadvantages of frictions are

1:- Friction opposes motion and stops moving objects.

2:- Machine parts get heated due to friction and thus, get damaged

3:- Friction causes wear and tear of materials like screws, ball-bearing, soles of shoes, tyres of vehicles.

4:- Friction causes wastage of energy.

 

13:- Why are the tyres of vehicles treated with many grooves?

 

Ans:- Tyres of vehicles are treaded with many grooves on their surface. These treads improve the grip of tyres on the road by increasing the friction between the tyres and the road. 

 

14:-Why are theSoles of shoes of athletes and mountaineers spiked?

 Ans:- Soles of shoes of athletes and mountaineers are spiked, for better grip and to prevent slipping.

 

15:- Why are Pavements and playing areas, such as basketball courts  made slightly rough?

Ans:- Pavements and playing areas, such as basketball courts, are made slightly rough to prevent slipping.

 

16:- What is the use of brake pads in break system?

Ans:- Friction is increased by using brake pads in the brake system of bicycles and automobiles. When we press the brake, these pads arrest the motion of the wheels due to friction.

 

17:- Why do the Kabaddi players rub their hands with soil?

Ans:- Kabaddi players rub their hands with soil for a better grip on their opponents.

 

18:- Why do the Gymnasts rub some coarse substance on their hands

Ans:- Gymnasts rub some coarse substance on their hands to increase

friction for better grip.   

19:- Write some methods which is used to reduce friction.

 

Ans:-  Some methods which is used to reduce friction are

 

1:-Friction is reduced by using ball bearing.

2:-Friction is reduced by using lubricants.

3:-Friction is reduced by polishing the surfaces.

4:- Friction is reduced by using wheels or rollers.

5:- Friction is reduced by using streamlining shape. Streamlined shape helps the object to moves through fluids. 

 

20:- What is streamlined shape?

 

Ans:- A body shape which offers very little resistance to the flow of air or water around it is called streamlined shape. A streamlined shape is like thin wedge or triangular objects lying on its base and sloping upwards gradually.

Ex:- boat , ship , aeroplane, bird, fish etc.

 

16:- What are lubricants?

Ans:-Lubricant is a substance used to reduce friction between surfaces. It is also used to reduces heat that is generated when two surfaces move on each other.  

 

17:- Why do sportsman use shoes with spikes?

Ans:- Sportsman use shoes with spikes to increase the force of friction between the shoes and the ground. The increased force of friction give them a better grip while running.

 

18:- Why does a ship have streamlined shape? 

Ans:- The streamlined shape is given to ship in the water to reduce the fluid friction. streamlined shape of ship cuts through the water very easily and thus increased their speed.

19:- Why do you slip when you step on a banana peel?

Ans:- We slip when we step on a banana peel because the inner side of banana peel being smooth and slippery reduces the friction between the sole of our shoe and the surface of road.

 

20:- How are tyres treaded to increase friction?

Ans:- When water is pushed away from the surface of road beneath the tyre, friction between road and tyre increases and improves the tyre grip on the wet road. The treaded tyres of cars, buses, trucks ,motorcycle ,scooter and bicycles provide better grip on the road. The players and athletes have to run fast. 

21:- Why is it difficult to write on a glass surface?

Ans:- Glass surface is so smooth that it does not provide friction to the tip of the pen. Hence, it is difficult to write on a glass surface. 

22:- Why is it difficult to drive on a wet road?

Ans:-  It is difficult to drive on a wet road because water creats a layer between the surface of rode and tyre which reduces friction. 

  

23:- Choose the correct option. (multiple choice question)

 

1:- Friction occurs because most are the surface are not-

1: plain       2: rough      3:smooth      4:hard

 

2:- Friction can be reduced by using-

1: lubricants      2: ball bearings      3: wheels       4: All of them

 

3:- Which of the following increases friction?

1: Lubricant      2: streamlining      3: polishing      4: treads on a tyre

 

4:-It is difficult to walk on ice because-

1: Friction is less             2: Friction is more    

3: pressure is low           4: pressure is high

 

5:- Friction is exerted by-

1: solid      2: liquid         3: gas          4: All of them

 

6:- Which of the following is a disadvantage of friction

1: Deformation of soles of shoe

2: Writing on paper and blackboard

3: Working of brakes on cycle and car

4: Truck tyres have grooves on it

 

7:- An irregular surface will have-

1: lesser friction                   2: greater friction    

3: zero friction                      4: lubricants

 

8:- To increase friction between field and shoes, athletic shoes are provided with-

1: Grooves       2: polish         3: Grease         4: Spikes

 

9:- Which of the following uses spikes in shoes?

1: Lawyers      2: doctors      3: mountaineers       4: painters

 

10:- Lubricant is used in scooters and bikes for which purpose?

1: As fuel                                      2:  For reducing friction    

3: For increasing friction           3: None of the above 

24:- Fill in the blanks

1: Friction is the force that ________ the relative motion between two surfaces in contact.  ( Ans:- oppose )

2: Friction is caused by ______ of irregularities on the surfaces in contact.  (Ans:- interlock )

 

3: Friction produces ______ . ( Ans:- heat )

 

4: We use ball bearings to ______ friction. (Ans:- reduces )

 

5: The smoother the surface, ______ will be the force of friction. 

  ( Ans:- lesser )

 

6:- Rolling friction is ______ than the sliding friction. ( Ans:- less )

 

7:- Least amount of friction required in ______ skating. 

    (Ans:-sliding )