THESE NOTES ARE PREPARED ACCORDING TO JKBOSE SYLLABI IN SIMPLIFIED AND CONCISE PATTERN
Questions:
1. State one way of increasing friction between two surfaces?
Ans: Friction can be increased between the two surfaces by making them rough.
2. Name four ways in which friction can be reduced between two surfaces?
Ans: Friction can be reduced by using the following methods:
1. Polishing the surface
2. Using a lubricant
3. Using a ball-bearing
4. Using telcum powder
5. Using soap solution
3. State two advantages of Friction?
Ans: Friction enables us to walk without slipping.
It helps a car to move on road without skidding.
It helps us to write on paper.
4. State two disadvantages of Friction?
Ans: The two disadvantages of friction are:-
1. It causes loss of energy in form of heat
2. It causes wear and tear of machines.
5. Why is friction called a necessary evil?
Ans: Since friction is very useful to us as It helps us to walk and drive car.
It is harmful in some cases eg It causes loss of energy, therefore, friction is called a necessary evil.
6. What is lubricant? What kind of lubricant can be used in a. Sewing machine b. Axil of tractor?
1. State one way of increasing friction between two surfaces?
Ans: Friction can be increased between the two surfaces by making them rough.
2. Name four ways in which friction can be reduced between two surfaces?
Ans: Friction can be reduced by using the following methods:
1. Polishing the surface
2. Using a lubricant
3. Using a ball-bearing
4. Using telcum powder
5. Using soap solution
3. State two advantages of Friction?
Ans: Friction enables us to walk without slipping.
It helps a car to move on road without skidding.
It helps us to write on paper.
4. State two disadvantages of Friction?
Ans: The two disadvantages of friction are:-
1. It causes loss of energy in form of heat
2. It causes wear and tear of machines.
5. Why is friction called a necessary evil?
Ans: Since friction is very useful to us as It helps us to walk and drive car.
It is harmful in some cases eg It causes loss of energy, therefore, friction is called a necessary evil.
6. What is lubricant? What kind of lubricant can be used in a. Sewing machine b. Axil of tractor?
Ans: Lubricant is substance used to reduce friction between two surfaces. eg Oil, Grease
In sewing machine oil is used where as in Axil of tractor, Grease is used.
7. Name two solid lubricants and state where they are used?
Ans: The two solid lubricants are:
1. Graphite: It is used in industries
2. Boric acid: It is used on carrom boards
8. What do you understand by term streamlining? Name a machine that uses streamline to reduce friction.
Ans: Streamlining means designing the body in such a way that it minimizes the force of friction.
Many machines are streamlined to reduce friction e.g Cars, Aeroplanes, Ships, Rockets, Drones etc
9. Why is friction called a pervasive force?
Ans: Friction is pervasive force.
Where as we cant write, walk or Run without friction. But friction causes wear and tear of materials, wastage of energy in form of heat.
Answer the following Questions.
i. Why are wornout tyres discarded?
Ans: Worn out tyres are discarded because they do not provide any friction. This can lead automobiles to skid off the road.
ii. Why do carrom coins move faster when dusted with telcum powder?
Ans: Telcum powder reduces the friction between Coins and board. Therefore carrom coins move faster.
iii. Why is surface of conveyor belt made rough?
Ans: The surface of conveyor belt is made rough to increase the friction between the belt and the materials upon it, So that the materials do not slip or fall down from the belt.
iv. Why is sewing machine often oiled?
Ans: The oil stops friction between the parts of machine. The friction can damage the parts of machine.
v. Why do new automobile tyres have deep groves?
Ans: Automobile tyres have deep grooves so that the tyres can have grip over the road. Due to these grooves the automobiles do not skid of the road.
vi. Why do a ball rolling on ground stop?
Ans: The ball rolling on the ground has two forces acting on it. The frictional force opposite to direction of motion and Gravitational force downwards. There forces make a ball to stop.
vii. Why are airplanes and boats given special shape?
Ans: The airplanes and boats have streamlined shapes. This helps them to reduce the friction due to air and water.
viii. Why do meteors burn on entering atmosphere?
Ans: When a meteor enters our atmosphere, Friction is caused between air and meteor. As meteors are not streamlined, Friction produces heat which burns the meteor.
ix. Why do painters use sand paper to polish doors?
Ans: The painters use sand paper to polish the doors to make the surfaces smooth. This makes the doors to shine.
x. Why is it easier to tie a knot on cotton string than silk?
Ans: The silk is very smooth as compared to the cotton fibre. In silk the amount of friction produced in knot will be very less than the cotton.
Fill in the blanks.
(Answers only)
I. Opposite II. Static III. Movement
Iv. Sliding V. Streamlined
Statements given below are wrong. Write the correct statements.
I. Sliding friction is slightly more than limiting friction
Ans: Slidinh friction is slightly less than limiting friction.
ii. The conveyor belt is made rough in order to decrease friction
Ans: The conveyor belt is made rough in order to decrease friction.
iii. The friction between two surfaces decreases with increase in weight of body.
Ans: The friction between two surfaces increases with increase in weight of body.
iv. The friction offered by wheels is called sliding friction
Ans: The friction offered by wheels is called rolling friction
v. The friction increases with increase in area of contact
Ans: The friction does not change with change in area of contact between two surfaces.
Ans: The friction offered by wheels is called rolling friction
v. The friction increases with increase in area of contact
Ans: The friction does not change with change in area of contact between two surfaces.
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