CHAPTER 11
FORCE AND PRESSURE
Here is some important points and answer of chapter 11 FORCE AND PRESSURE NCERT science of class 8.These important points help the student to better understanding of the topic of CHAPTER 11 FORCE AND PRESSURE OF CLASS 8. The complete solution of CHAPTER 11 FORCE AND PRESSURE is given here which is prepared subject expert.
Important Points:-
a) Force:- A push or pull of an object is called force.
b) Nature of Force:- Force applied on an object in the same direction add to one another and if two forces acting on an object in opposite direction then the net force is the difference of between the two forces.
c) Contact force:- When a force is applied physically through a direct contact between two object.
Example:- Muscular force and Frictional Force.
d) Non contact force:- When a force is applied between bodies without being in contact with each other are known as non contact force. For example:- electrostatic force and gravitational force.
e) Muscular force:- It is a contact force which is applied by the muscles of the body. For example:- While lifting the school bag you apply force using muscles of your arm.
f) Frictional Force:- The force acting between two surface in contact and tends to oppose motion is called frictional Motion. It is a contact force which slows down or stops the moving object. For example:- Rolling ball on the ground stops due to friction.
g) Electrostatic force:- Force applied by a charge body on another changed or unchanged body is called electrostatic force. For example:- a straw rubbed by a paper attracts another shtraw which is not rubbed.
h) Magnetic force:- The force exerted by a magnet on a piece of metal or another magnet is known as Magnetic force. Example:- Magnet attracts piece of iron without being in contact with it.
i) Gravitational force:- The force exerted by earth due to which object falls on the earth is called the Force of Gravity or Gravitational force.
These are some important points of CHAPTER 11 FORCE AND PRESSURE of Class 8 Science NCERT.
Here is the answer of textbook Questions of Chapter 11 FORCE AND PRESSURE.
Ques 1. Give two examples each of situations in which you push or pull to change the state of motion of object.
Ans. A Boy kicking a football at rest, and the force exerted on a perambulator to move it from rest, are example of push.
The force exerted by a bullock on a cart and the force exerted to drag a chair are the examples for pull.
Ques 2. Give two examples of situation in which applied force causes a change in the shape of an object.
Ans. Squeezing a lemon and inflating a balloon are examples in which applied force cause a change in shape of an object.
Ques 3. Fill in the blanks:-
a) To draw water from a well,we have to ______ at the rope.
b) A charged body __________ an uncharged body towards it.
c) To move a loaded trolly we have to ________ it.
d) The north pole of a magnet __________ the north pole of the other magnet .
Ans. a) Pull
b) Attracts or pull
c) Pull or push
d) Repels or push
Ques 4. An archer stretches her how while taking aim at the target. She then release the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statement using the following terms.
a) To stretch the bow, the archer applied the force that causes the change in its _________.
b) The force applied by the archer to stretch the bow, is an example of _________force.
c) The type of force responsible for a change in the state of motion of the arrow is an example of__________ force.
d) While the arrow move towards its target, the force acting on it are due to __________ and that due to ________ of air.
Ans. a) Shape
b) Muscular
c) Contract
d) Friction
Ques 5. In the following situation identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
a) Squeezing a piece of lemon between the fingers to extract it's juice.
b) Taking out paste from the toothpaste tube.
c) A load suspended from a spring while it's other end is on a hook fixed to a wall.
d) An athlete making a high jump to clear the bar at a certain height.
Ans.a) The agent exerting the force is the fingers. The object on which the force acts is the lemon. And the effect of the force is the extraction of the juice from the lemon.
b) The agent exerting the force is the fingers of the hand. The object on which the force acts is the toothpaste tube. And the effect of the force is extraction of the paste from the toothpaste tube.
c) The agent exerting the force is the weight of the suspended load the object on which the force acts is the spring. And the effect of the force is the stretching of spring along its length.
d) The agent exerting the force is the reaction of the ground on the athlete. The object on which the force acts is the athlete and the effect of the force is athlete.
Ques 6. A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering effect the price of iron?
Ans. When the Blacksmith hammers a hot piece of iron the force due to hammering change the shape of the iron piece.
Ques 7. A inflated balloon was pressed against a wall after it had been rubbed with a piece of synthetic fibre. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Ans. When the inflated balloon is rubbed with a piece of synthetic cloth. It get changed due to friction. When the balloon is pressed against the wall,the electronic force between the balloon and the wall is responsible for the attraction between the balloon and the wall.
Ques 8. Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the force acting on the bucket do not bring the change in its state of motion.
Ans. The force acting on a plastic bucket containing water held above ground level in my hand are:-
i) The gravitational force of attraction on the bucket exerted by the earth acting vertically downwards.
ii) The reaction of the hand on the bucket acting vertically upwards. The two forces are equal in magnitude and opposite in direction so there resultant force on the bucket is zero. Hence, they do not bring about any change in the buckets state of motion.
Ques 9. A rocket has been fixed upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Ans. When a rocket is fired upwards, the two forces acting on it immediately after leaving the launching are:-
I) The gravitational force of attraction exerted on the rocket by the earth, acting vertically downwards.
II) The thrust exerted by the ejecting gases on the rocket acting vertically upwards.
Ques 10. When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
a) pressure of water.
b) gravity of the earth.
c) shape of rubber bulb.
d) atmospheric pressure.
Ans.d) atmospheric pressure.
This is the complete solution of CHAPTER 11 Force and Pressure. This is according to latest syllabus of CBSE 2020-21.
Here's some extra questions are given according to CHAPTER 11 Force and Pressureof class 8 Science NCERT.
Ques 1. Define pressure and write it's formula.
Ans. Pressure is defined as the force acting or a unit area of the surface is called pressure.
Pressure= Force/Area.
Ques 2. What are the factors in which pressure in solid depends?
Ans. Pressure in solid depends on the force and the area on which it acts. The smaller the area,larger will be the pressure for the same force, if the force is greater than pressure will also be greater for same area.
Ques 3. What are the two factors on which pressure in liquid depends?
Ans. Pressure in liquid depends upon two factors:-
I) The height of the liquid columns.
II) Density of the liquid.
Ques 4. What are fluids?
Ans. The matter that has a tendency to flow are known as Fluids. All liquids and gases are fluids.
Ques 5. What are atmospheric pressure?
Ans. The pressure exerted by air of atmosphere is called the atmospheric pressure.
These are some extra Questions of Chapter 11 Force and Pressure of class 8 Science NCERT.
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