These questions are designed with the help of a highly trained and technical team. We have divided CBSE CLASS 8 Force and Pressure Questions under various heads such as Very Short answers, Short answers, Long answers, and Higher Order Thinking Skills.
Very Short Type Questions
Q 1. Define Force.
Ans. A push or pull on an object is called force. It is the interaction of one object with another object which results in a force between the two objects.
Q 2. What is the name of the instrument used to measure atmospheric pressure?
Ans. Barometer
Q 3. Give two examples of contact force.
Ans.
- Muscular force.
- Force of friction.
Q 4. Name the force exerted on a ball of dough to make a flat chapati.
Ans. Muscular force
Q 5. What kind of force is an electrostatic force?
Ans. Non-contact force
Q 6. Is gravity a property of earth only?
Ans. No, Gravitational force is a universal force.
Q 7. Name the force due to which every object falls on earth.
Ans. Gravitational force
Q 8. What do you mean by pressure?
Ans. Force per unit area. Pressure = (Force/Area)
Q 9. Do liquids and gases also exert pressure?
Ans. Yes
Q 10. What are the two states of motion?
Ans. The state of rest, The state of motion.
Q 11. What kind of force is friction?
Ans. Contact force
Q 12. What type of force is gravitational force?
Ans. Non-contact force
Q 13. Is it true that force acting on an object can also change its shape?
Ans. Yes, it is true.
Q 14. While sieving grains, small pieces fall down. Which force pulls them down?
Ans. Gravitational force
Q 15. How can we change the speed and the direction of a moving body?
Ans. By applying force.
Q 16. What is the distance moved by an object in unit time called?
Ans. Speed
Q 17. Does the force of gravitation exist between two astronauts in space?
Ans. Yes
Q 18. How electricity charges can be produced?
Ans. Electric charges can be produced by friction when one object is rubbed over another object.
Q 19. What does the state of rest mean?
Ans. The state of rest is considered to be the state of zero speed.
Q 20. What is the similarity between electrostatic and magnetic forces?
Ans. Both are non-contact forces. Both are attractive as well as repulsive forces.
Q 21.What causes motion in objects ?
Ans. The motion imparted to objects is due to the action of force.
Q 22. Is muscular force a contact? force? Why?
Ans. Yes, muscular force is a contact force, since muscular force can be applied only when it is in contact with an object.
Q 23. Where does friction act and what is its direction?
Ans. Friction acts on all the moving objects and its direction is always opposite to the direction of motion of the object.
Q 24. Is friction a contact force? Why?
Ans. Yes, friction is a contact force. Since the force of friction arises due to contact between surfaces.
Q 25. What is the SI unit of pressure?
Ans. Pascal (Pa) .
1 Pa = 1 N/m2 or 1 newton per square metre .
Q 26. At least how many objects are needed to apply a force?
Ans. At least two objects are needed to apply a force.
Q 27. Give one example of gravitational force.
Ans. An apple falling from the tree to the ground.
Q 28. What infers the change in the state of motion of an object?
Ans. A change in either the speed of an object, or its direction of motion, or both, is described as a change in its state of motion.
Q 29. What has to happen for a force to come into play ?
Ans. At least two objects must interact for a force to come into play.
Q 30. A force of 100 N is applied on an area of 4 m2. Compute pressure being applied on the area.
Ans. Given: Force = 100 N, Area = 4 m2
∴ Pressure = 25pa.
Q 31. Define 1 Newton of force.
Ans. 1 Newton is the force which can make an object of 1 kilogram mass to move at a speed of 1 metre per second.
Q 32. What do you mean by magnitude?
Ans. The strength of a force is usually expressed by its magnitude.
Q 33. What is muscular force?
Ans. The force resulting due to the action of muscles is known as muscular force.
Q 34. What is meant by atmospheric pressure?
Ans. The weight of the atmosphere exerts pressure on the surface of the earth and on all the objects on the earth, including ourselves. This pressure is known as atmospheric pressure.
Q 35. What is interaction?
Ans. Interaction of one object with another object results in a force between the two objects. If both the objects are capable of applying force on each other, then the interaction between them can be of ‘pushing’ and ‘pulling’.
Q 36. Define Electrostatic force.
Ans.
- The force exerted by an electrically charged object is known as electrostatic force.
- A plastic comb (or plastic pen) which is electrically charged by rubbing in dry hair, exerts an electrostatic force on uncharged tiny pieces of paper and attracts them.
Q 37. Give an example of force from our everyday life.
Ans. Force is used in our everyday actions like
- Picking
- Opening
- Shutting
- Kicking
- Hitting
- lifting
- Flicking
- Pushing
- Pulling
- pressing.
Q 38. What is contact force?
Ans. Force that can be applied only when it is in contact with an object is called contact force.
- Muscular Force, and
- Frictional Force (or Friction).
Q 39. What do you mean by the term atmosphere and atmospheric pressure?
Ans. This envelope of air is known as the atmosphere. The atmospheric air extends up to many kilometres above the surface of the earth. The pressure exerted by this air is known as atmospheric pressure.
Q 40. Define Friction.
Ans. The force which always opposes the motion of one body over another body is called frictional force (or friction).
Here see the point of contact between the shoe and the Ground.
Q 41. What are the two types of charges?
Ans. The electric charges are of two types:
- Positive electric charges
- Negative electric charges
Q 42. Define pressure.
Ans. The force acting per unit surface area is called pressure. SI unit of pressure is measured in (Newton/Metre2 ), which is equal to 1 Pascal (Pa).
Q 43. What happens to a body in motion along a circle ?
Ans. When a force makes a body to move in a circle, then its velocity changes at every point in the circular path due to change in direction.
Q 44. Which force is responsible for the downward movement of a parachutes? Will he come down with the same speed without the parachute?
Ans. Force of gravity is responsible for this downward movement. No, without a parachute he will come down with a higher speed.
Q 45. Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.
Ans. Electrostatic force is responsible for this phenomenon. The two balls have similar charges, that’s why they move away due to repulsion between them.
Q 46. What does muscular force enable us to do?
Ans. Muscular force enables us to carry out our physical activities and other tasks. It helps us in movement, locomotion, bending of different parts of our body, lifting, kicking, pushing or pulling objects, etc.
Q 47. An airplane is flying in the sky. Identify any two forces acting on it.
Ans. The two forces acting on the Airplane are as follows:-
- Weight in downward direction.
- Air Lift in upward direction.
Q 48. What happens if the force is applied in the direction of motion of the body ?
Ans. If the applied force is in the direction of motion of the body, the speed of the body increases.
Q 49. What happens if the force is applied in the direction opposite to the motion of the body?
Ans. If the force is applied in the direction opposite to the motion of a body, then it results in a decrease in the speed of the object. The body may also come in a static state.
Q 50. Can force of gravity act on all distant objects ?
Ans. Yes, force of gravity is not restricted to near or distant objects. It acts on all the objects.
Q 51. Do gases exert pressure? Where?
Ans. The gases also exert pressure. They exert pressure on the walls of the container in which they are filled.
Q 52. Give one example which demonstrates the sideways pressure exerted by water?
Ans. A liquid exerts pressure in all directions – even upwards. Actually, the pressure at any point in a liquid acts equally in all directions (even upwards).
Q 53. Define the force of gravity?
Ans. The force with which the earth pulls the objects towards it, is called the force of gravity (or just gravity). The force of gravity causes all the objects to fall towards the earth.
Short Type Questions
Q 54. Why muscular force is known as contact force?
Ans.
- Since muscular force can be applied to an object only when our body (or body of an animal) is in contact with the object; therefore, muscular force is a contact force.
- For example, when we lift a book from a table by applying muscular force, then our hand is in contact with the book. We cannot lift the book from table without touching it.
Q 55. Why the bicycle moving on the road slows down and finally comes to a stop?
Ans. 1) The bicycle moving on the road slows down and finally comes to a stop due to the frictional force between the tyres of the bicycle and the road.
2) This frictional force opposes the motion of bicycle and brings it to a stop. In this case, the two surfaces in contact are the road and surface of tyres of bicycle.
Q 56. Which effects can be produced by Force ?
Ans. A Force can produce the following effects :
- A Force can move a stationary object.
- A Force can stop a moving object.
- A Force can change the speed of a moving object.
- A Force can change the direction of a moving object.
- A Force can change the shape (and size) of an object.
Q 57. How do fluids exert pressure?
Ans. All the liquids have weight . So, When we pour a liquid into a vessel, then the weight of liquid pushes down on the base of the vessel (or bottom of the vessel) producing a pressure.
Therefore the weight of this liquid pushes on the base of the vessel and exerts a pressure on the base of the vessel. Moreover, Fluids exert pressure in all directions – even upwards. Fluids also exert pressure on the walls of the container in the sideways direction that hold them.
Fig.1 Fig.2 Fig.3 Fig.4
In Fig.1 the liquid is exerting pressure in the Downward direction on the attached Rubber Balloon .
In Fig.2 the liquid is exerting more pressure in the Downward direction on the attached Rubber Balloon .
In Fig.3 the liquid is exerting pressure in the sideways direction on the attached Rubber Balloon .
In Fig.4 the liquid is exerting equal pressure in the sideways direction on the attached Rubber Balloon
Q 58. How nose bleeding takes place at high altitudes?
Ans.
- At high altitudes, the atmospheric pressure becomes much less than our blood pressure.
- Since our blood is at a higher pressure than outside pressure, therefore, some of the blood vessels in our body burst and nose bleeding take place at high altitudes.
- Thus, nose-bleeding usually occurs in those persons who trek to high mountains (where the atmospheric pressure is much less than our blood pressure).
Q 59. How does an applied force changes the speed of an object?
Ans. If the applied force is in the direction of motion, the speed of the object increases. But if the force applied in the direction opposite to the motion, then it decreases the speed of the object.
Q 60. Name the forces acting on the car sticking to an electromagnet in a Junkyard. Which one of them is larger?
Ans. Magnetic force (in the upward direction) and force of gravity or the weight of the car (downward). Magnetic force is larger than the force of gravity.
Q 61. What do two magnets do on each other when they are brought close?
Ans. Two magnets with like poles exert a force of repulsion on each other and two unlike poles attract each other. A magnet can exert forces on another magnet without being in contact with each other.
Q 62. What are contact and non-contact forces? Give two examples each.
Ans.
Contact forces: A contact force is a force which acts on an object when comes in physical contact with it. The most familiar examples of a contact force are muscular force and frictional force.
Non-contact forces: A non-contact force is a force which acts on an object without coming physically in contact with it. The most familiar examples of a non-contact force are:
- Magnetic Force,
- Electrostatic Force, and
- Gravitational Force.
Q 63. What is meant by the state of motion and the state of rest?
Ans.
- The state of motion of an object is described by its speed and the direction of motion.
- The state of rest is considered to be the state of zero speed.
Q 64. Give some examples to support that application of a force on an object may change its shape.
Ans. Some examples to support that application of a force on an object may change its shape are as follows :-
- When a force is applied on an inflated balloon by pressing it between two palms, the shape of the balloon undergoes a change.
- The shape of a ball of dough changes when it is rolled to make a chapati. The roller applies the force in this case.
Q 65. Define friction. How does friction act?
Ans. Friction is a kind of force which arises between two surfaces in contact. The two surfaces in contact may be solid, liquid or gaseous. The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion.
Q 66. What is a force of gravity? Give some examples to show that it is an attractive force.
Ans. Objects or things fall towards the earth because it pulls them. This force is called the force of gravity or just gravity. It is an attractive force.
Examples which show that gravity is an attractive force :
(1) Water begins to flow towards the ground as soon as we open a tap.
(2) Water in rivers flows downward due to the force of gravity.
Q 67. Discuss the characteristics of the force of gravity:
Ans. Characteristics of the force of gravity:
- The force of gravity is an attractive but non-contact force.
- This force acts on all objects on or near the surface of the earth.
- The force of gravity acts On all things including us all the time without their being aware of it.
Q 68. Why does a car or a scooter come to rest once its engine is switched off?
Ans. Only frictional force acts immediately after the vehicle is switched off. Vehicles only moves, when their mechanical force exceeds the frictional force. But when engine is switch off, the mechanical force becomes zero but frictional force persist. This brings vehicle (car or scooter) to rest.
Long Type Questions
Q 69. What is force? State the difference between contact force and non-contact force.
Ans.
| Contact force | Non-contact force |
| Force that can be applied only when it is in contact with an object is called a contact force, e.g., muscular force, frictional force | The force exerted on an object without touching it is known as non-contact force, e.g., gravitational force, magnetic force |
Q 70. Define the different types of forces.
Ans. Force can act on a body from a distance or by being in contact with it. Depending on this, forces can be classified as contact and non-contact forces.
Contact forces: When force is applied to an object by direct or indirect physical contact the applied force is called contact force. The muscular and frictional force is an example of contact force.
Muscular force: The force resulting due to the action of muscles is known as the muscular force.
Frictional force: The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
Non-contact forces: When a force is applied to an object by another body that is not in direct contact with it is called non-contact force. Gravitational, magnetic and electrostatic force is example of noncontact force.
Gravitational force: The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity.
Electrostatic force: The force exerted by an electrically charged object is known as electrostatic force.
Magnetic force: The force exerted between a magnet and other magnet or magnetic material is known as a magnetic force.
Q 71. Why it is easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)?
Ans. A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the ‘flat’ shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.
Q 72. What is pressure? What is the relation of pressure with area on which it is applied?
Ans. Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we can conclude that pressure increases with decrease in area.
Pressure = Force/ Area
Q 73. List the characteristics of pressure exerted by a liquid.
Ans.
- Liquid exerts pressure in all directions.
- Pressure in liquid does not depends on shape, size and surface area of the container.
- Pressure increases with depth.
- All points at the same level in a liquid are at the same pressure.
- Pressure does not depend on the surface of the immersed object.
Q 74. (a) How does the medicine or water enter a dropper? Explain the mechanism.
(b) Name the type of force in the following cases:
(i) Ruminate falling on the earth.
(ii) Running a comb through dry hair.
(iii) A bar magneto suspended freely.
Ans.
(a) 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. On releasing the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to atmospheric pressure which is acting on the water or the medicine and makes it rise in the dropper.
(b) (i) Gravitational force or gravity
(ii) Electrostatic or electric force
(iii) Magnetic force
Q 75. Write the answer of following questions:
(a) Why is it comfortable to lift a school bag with broad straps than thin straps?
(b) Give an example to show that force can change the shape of an object.
Ans.
(a) Broad straps have larger area and decrease the pressure of the weight of the bag on the shoulders. But if the straps are thin the shoulders will be under large pressure and will be painful. That’s why we feel comfortable with a bag with broad straps.
When we apply a force on an inflated balloon by pressing it between our palms the shape of a balloon changes. When a force is applied on the dough, it is rolled to make a Chapati.
(b) When we apply a force on an inflated balloon by pressing it between our palms the shape of a balloon changes. When a force is applied on the dough, it is rolled to make a Chapati.
Q 76. Define the different types of forces.
Ans. Force can act on a body from a distance or by being in contact with it. Depending on this, forces can be classified as contact and non-contact forces.
(a) Contact forces: When force is applied on an object by direct or indirect physical contact the applied force is called contact force. Muscular and frictional forces are examples of contact force.
(b) Muscular force: The force resulting due to the action of muscles is known as the muscular force.
Frictional force: The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each
other.
(c) Non-contact forces: When a force is applied to an object by another body that is not in direct contact with it is called non-contact force. Gravitational, magnetic and electrostatic forces are examples of non-contact forces.
(d) Gravitational force: The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity.
(e) Electrostatic force: The force exerted by a charged body on another charged or uncharged 1 body is known as electrostatic force.
(f) Magnetic force: The force exerted between a magnet and other magnet or magnetic material is known as a magnetic force.
Q 77. Why electrostatic force is an example of Non-contact force ?
Ans. The electrostatic force can be exerted by the object of a charge on another object from a distance (even when they are not in touch with each other). So, an electrostatic force is an example of a non-contact force.
Q 78. Why the gravitational force is an example of non-contact force?
Ans. The gravitational force of earth (or gravity) acts on objects from a distance (without there being a physical contact), therefore, the gravitational force of gravity is an example of non-contact forces.
Q 79. Why the tip of sewing needle is sharp?
Ans. The tip of a sewing needle is sharp so that due to its sharp tip, the needle may put force on a very small area of the cloth, producing a large pressure sufficient to pierce the cloth being stitched.
Q 80. Why small heels tend to sink deep into soft sand?
Ans. 1. A small heel (or sharp heel) has a small area in contact with the soft sand and so exerts a greater pressure on the soft sand.
2. Due to this greater pressure, the small heels tend to sink deep into soft sand making it difficult for the wearer to walk on soft sand.
Q 81. Why pressure increases with increasing depth?
Ans. The pressure exerted by a liquid increases with increasing depth inside the liquid. The pressure exerted by a liquid is small just under the surface of the liquid. As we go deeper in a liquid, the pressure of liquid increases. Actually, as the depth of liquid increases, the weight of liquid column pushing down from above increases, and hence the pressure also increases.
Q 82. Why the wall of a dam is made thicker at the bottom?
Ans.
- The sideways pressure of a liquid on the walls of a vessel is almost zero at its surface. As the depth of liquid increases, the sideways pressure on the walls of the vessel gradually increases and it becomes maximum near the bottom of the vessel.
- The wall of a dam is made thicker at the bottom (than at the top) so as to tolerate very high sideways pressure exerted by deep water stored in the reservoir of dam.
Q 83. How Air Pressure is created ?
Ans.
- Air pressure arises due to the constant collisions of the tiny molecules of the gases present in air with the walls of the container (for vessel) in which it is enclosed.
- If certain mass of air is compressed into smaller volume (say, by using a pump), then the number of collisions of air molecules per unit area increases, and hence the pressure exerted by air goes up.
- If the container of air has stretchable walls (like a rubber balloon), then the higher pressure excreted by air inflates the container (increases the size of the container and makes it look bigger).
Q 84. Give the two examples of the gases exerting pressure.
Ans. The air pressure which we have just described is due to the motion of molecules of gases present in air which is enclosed in a container in a container (like balloon or football).
- When air is filled into a balloon with our mouth, the balloon gets inflated (gets bigger in size).
- When air is filled into a bicycle tube with a pump, the tube gets inflated and makes the tyre feel ‘hard’.