Lakhmir Singh and Manjit Kaur Science solution: Friction Chapter 12. Here you get easy solutions of Lakhmir Singh and Manjit Kaur Science solution Chapter 12 . Here we give Chapter 12 all solution of Class 8. Its help you to complete your homework.
Board – CBSE
Text Book – SCIENCE
Class – 8
Chapter – 12
VERY SHORT ANSWER TYPE QUESTIONS
3) a> Smooth surface. b> rough surface.
4) Opposite to the direction in which the object moves.
5) spring balance.
6) Spring balance is an device which is used for measuring force acting on an object.
7) a> Sliding friction. b> static friction.
8) Rolling friction.
9) Because the friction on the smooth surfaces is very small.
10) Because the friction on wet marble floor becomes very small which cannot prevent us from sleeping.
11) When the vehicle on the road, due to the friction the cars of tyres wearing out.
13) Frictional force.
14) Frictional force.
17) To increase friction and a better grip on their opponent players.
18) To increase friction.
19) Ball bearing.
20) To reduce friction.
21) Heavy suitcase, Cycle.
22) Ball bearing.
23) To moving heavy suitcase.
24) To reduce friction and increase efficiency.
26) Oil, Grease.
27) To reduce friction between carom board and coins and strikers can move easily on carom board.
29) To prevent injury by its friction.
30) Frictional force.
31) Fluid friction
33) To increase friction with the ground and to get a better grip on a slippery ground.
34) Because water on the road may squirt out from between the threads and increase friction between tyres and wet road.
35) a> Motion, b> Less, c> Heat, d> Slipping, e> reduces, f>roll, g> drag. h> Streamlined, i> Streamlined, j> Streamlined, k> Bird.
SHORT ANSWER TYPE QUESTION
36) Friction preventing this box to move forward.
The force acts in a direction opposite to the direction in which an object moves.
38) A rough surface.
Because a rough surface has a more frictional power than smooth surface.
39) When an object has already started moving, the irregularities on its surface do not get enough time to lock into the irregularities on the surface of the other object completely. Since the interlocking of the two surfaces is less when an object has already started to moving.
40) When an object rolls over the surface of another object, the resistance to its motion is called rolling friction.
41) Seema have to apply a larger force.
Because heavier box means large friction force, and large friction force means it will be need to apply a larger force to move that heavier box.
42) 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.
43) Because of Ice molecules on the road, car wheels have low traction or low friction on the road. That’s why car wheels often spin on icy roads.
44) (a) We cannot write with a pencil on a glass sheet because the glass surface is very smooth due to which the friction between the tip of pencil and glass surface is much less. This friction is not sufficient to rub off black graphite.
(b) We cannot climb on a greasy pole because greasy pole will be slippery and we cannot get enough friction to climb on that pole.
45) The friction between the head of matchstick and rough side of matchbox produce heat because of the chemical present on the head of matchstick. That’s why matchstick catches fire and starts burning.
46) Because enough friction is not provided by a smooth surface to produce sufficient heat.
47) The sole is the part wear away first in shoes.
because it is below the shoe and the only part that is in direct contact with earth.
48) The bicycle brake pad gets worn out due to friction between brake pad and moving rim of bicycle.
49) Because of the friction between eraser and the paper, the pencil eraser loses tiny pieces of rubber each time we use.
50) Our hands will be warm if we rub our hands vigorously for a few seconds. Because of the friction during rubbing our hands, few amount of heat created in our hand.
51) Friction enables to walk on ground because friction between the sole of our shoes and ground prevents us from slipping over the ground.
52) A Kulhar.
Because a kulhar have a rough surface and it is easy to hold this with our hands.
53) When brakes are applied, a friction is created between rim of the cycle and the brake. This friction stops the bicycle.
54) Soles of our shoes wear out gradually because of the friction between sole and the road.
55) Friction between the surface of tyres and the surface of road breaking tiny pieces of rubber from the tyre’s surface after that tyre are worn out .
56) Two advantages of friction:
- Friction enables us to walk without slipping.
- Friction enables a car to move on road without skidding.
Two disadvantages of friction:
- Friction wears away the soles of our shoes.
- Friction wears out the rubbing machine parts.
57) Sportsman use shoes with spikes to increase friction and prevent slipping.
58) We can reduce friction using oil or grease to those machine parts when rub each other.
59) Machine are lubricated with oil or grease to reduce friction, this method called friction .
60) Wheels are so useful because it can reduce the friction of a heavy suitcase, etc.
61) Lubricants applied to rubbing surface of machine to reduce friction and also helps to avoid interlocking between two rubbing surface.
63) Car, aeroplanes and rockets are streamlined because to reduce air resistance.
64) A speedboat has a streamlined shape to reduce the frictional force of water.
65) The substance which are able to flow easily are called fluids.
The two common fluids are Water and air.
LONG ANSWER TYPE QUESTIONS :
66)(a) The force which always opposes the motion the motion of one object over another object in contact with it is called friction.
The factors affecting friction are
- The nature of the two surface
- The force with which two surfaces are pressed together.
Example : When we push a heavy box kept on floor, the force of friction occurs between the surface of floor and the bottom of the box.
(b) Friction is caused by the interlocking of irregularities in surface of the two objects which are in the contact with each other.
|Static friction||Sliding friction|
|Maximum frictional force present between any two objects when one object just tends to move||Frictional force present when one object moves slowly over the surface of another object is known as sliding friction.|
|The object is actually not moving or sliding over the other object||The object is already in motion than to move the same object from rest.
69) The frictional force exerted by a fluid is called drag.
The two examples of drag are: air resistance, friction force in water.
70) (a) The fluid friction can be reduced or minimized by giving special shape is called ‘streamlined shape’
Car is an object which usually has a streamlined shape.
(b) Objects moving in fluids have should have streamlined shape because to reduce fluid friction. sss