Lakhmir Singh and Manjit Kaur Science solution: Force and Pressure Chapter 11. Here you get easy solutions of Lakhmir Singh and Manjit Kaur Science solution Chapter 11 . Here we give Chapter 11 all solution of Class 8. Its help you to complete your homework.
Board – CBSE
Text Book – SCIENCE
Class – 8
Chapter – 11
VERY SHORT ANSWER TYPE QUESTIONS answer
2)Due to force by air and water.
6)Pulling from both the side
(c) Push and pull
(f) Push and pull
8) Magnetic force.
10) Magnetic force.
17)water experts pressure on the walls of its container.
18) Atmospheric pressure.
19) Blood Pressure.
- Top of high mountain.
23)High air pressure.
25)20 m. below the surface of sea.
29) a> False, b>False
30) A> Pull, B> Zero, c> push, pull, D> direction, e> Interaction. f> attracts g> repels, h> Pressure. i> increase. J> atmosphere. K> Decrease,
SHORT ANSWER TYPE QUESTIONS Answer
31)The state of motion of an object is defined by its velocity – the speed with a direction. An object at rest has zero velocity and (in the absence of an unbalanced force) will remain with a zero velocity.
The agent can change the state of motion of an object when a body is moving
friction or unbalanced force.
32)The two examples are drawing a bucket of water from a well moving a wheel barrow.
33)It means that an interaction of one object with another object results in a force between the two objects.
Illustration: Suppose a man is standing behind a stationary car. There is no interactive between the man and the car and no force acts on the car and hence the car does not move. Now if the man pushes the car with his hands due to which the car starts moving.
34)Here the equal and opposite forces applied on the rope.
35)A push or pull on an object called force.
The various effect of force are :
- A force can move a stationary object.
- A force can change the direction of a moving object.
36)(a) Take a rubber ball and place it on a table top, then gently push the ball along the surface of table and then we will observe that the ball begins to move.
(b) Take a rubber ball and place it on a table top, then gently push the ball so that it will starts moving. Now place your palm in front of the moving ball. We will observe that the moving ball comes to a stop.
37)(a) When we are moving on a bicycle at a certain speed, then if someone pushes the moving bicycle from behind then the speed of bicycle increases and it will move faster
(b) In the game of carom, when we take a rebound, then the direction of striker changes. This is because the edge of the carom boards exerts a force on a striker.
38) Atmospheric pressure.
39) When we sit on a sofa with springs, then the springs of the sofa get compressed and their shape and size changed.
40) The various kind of forces are : Muscular force, Frictional force, Magnetic force, Gravitational force.
41)The force exerted by the muscles of the body is called muscular force.
Example : Lifting.
42)Magnetic force, gravitational force, electrostatic force.
44)A rubber sucker is a device made of rubber that sticks firmly to flat and smooth surfaces on pressing.
When we press the rubber sucker on a flat, smooth surface, its concave rubber cup gets flattened to a large extent, pushing out most of the air from beneath it. The much greater atmospheric pressure acting on the rubber sucker from outside fixes the rubber sucker firmly on the flat surface.
Rubber sucker are used to hold glass onto the wooden frames of tables.
45)At high altitudes, the atmospheric pressure becomes much less than our blood pressure. So that’s why mountaineers usually suffer from nose-bleeding.
46)The filling of ink in a fountain pen is also based on the existence of atmospheric pressure.
47)Water comes out more slowly than the from the upstairs tap than a similar tap downstairs because the pressure of water in downstairs is higher than the upstairs.
48) Gravitational force means the pull exerted by objects possessing mass is called gravitational force.
Example: When a diver dives into a swimming pool, it is the force of gravity which bring him down.
49) a> 20 Pa, b> 40 Pa
50) Muscular force.
52)a> Muscular force, b> Magnetic force. c> Gravitational force. d> electrostatic force, e> Frictional force.
53)A sharp knife has a very thin edge to its blade and it cuts object better, but on the other hand, a blunt knife has a thicker edge and also it does not cut an object easily. So a sharp knife cut objects more effectively than a blunt knife.
54)Wooden sleepers are kept below the railway line, so that there is less pressure of the train on the ground and railway line may not sink into the ground.
55)A wide steel belt is provided over the army tank wheels so that they exert less pressure on the ground and do not sink into it.
56)The tip of a sewing needle is sharp because a sharp point can create pressure in a less area and it can sew clothes easily.
57)When we wear snow shoe, it helps us to expand our foot or walking area during walk into snow, that’s why we don’t sink when we use snow shoe.
58) Due to the weight of man falls on a small area of the cushion producing a large pressure. This large pressure causes a big depression in the cushion. On the other hand, when the same man is lying on the cushion, in this case the weight of man falls on a much on a much large area pressure produces a very little depression in the cushion.
59) Porters place a thick, round piece of cloth on their head because the porters increase the area of contact of the load with their head. Since the load now falls on a larger area of head, the pressure on head is reduced and it becomes easier to carry the heavy load.
60) For making compass .
LONG ANSWER TYPE QUESTIONS Answer
61)(a) A force which can be exerted by an object only through ‘physical touching ‘ is called a contact force.
Example: A book is lying on the table, to lift this book from the table, some force are required. When we lift this book from the table by hand, the force is exerted by the muscle of our arm.
(b) A force which can be exerted by an object even from a distance is called a non-contact force.
Example: A magnet attracts things made of iron. If we bring a magnet near iron nails or pins, the magnet pulls them towards it. Since the iron nails and pins move towards the magnet, it means that the magnet exerts a force on them.
62)(a) The force which always opposes the motion of one body over another body is called frictional force.
(b) The frictional force arises only when the surfaces of two objects are in touch with each other, so the frictional force is an example of a contact force,
(c) A magnet can exert a force on another magnet even from a distance without touching the other magnet. That’s why magnetic force exerted by one magnet on the other magnet is an example of a non-contact force.
63)(a) Pressure is the force acting on a unit area of the object.
Pressure is measured in Pascal (Pa).
(b) A school bag has wide strap that’s why the weight of bag may fall over a large area of the child producing less pressure on the shoulder, so less pressure, it is more comfortable to carry the school bag.
6)4)(a)The weight of atmosphere exerts a pressure on the surface of the earth and on all the objects on the earth, including ourselves, this pressure is known as atmospheric pressure.
The cause of the Atmospheric pressure is due to the weight of air present in the atmosphere.
(b) In our body, blood exerts a pressure called ‘blood pressure’ which is slightly greater than atmospheric pressure. The atmospheric pressure acting on our body from outside is balanced by the blood pressure acting from inside. That’s why our body not crushed by the large pressure exerted by the atmosphere.
(c) When we go higher up above the earth’s surface, the air surface become thin so the atmospheric pressure become decrease.