Force and Pressure Class 8 Science Important Questions Chapter 11
Force and Pressure Class 8 – Multiple Choice Questions
Q 1 – The pressure which is exerted by the air around us is known as (1)
(a) force
(b) atmospheric pressure
(c) muscular force
(d) friction
Ans – (b) atmospheric pressure
Q 2 – Force acting on per unit area is called (1)
(a) non-contact forces
(b) contact forces
(c) force
(d) pressure
Ans – (d) pressure
Q 3 – The force exerted by the earth to pull the object towards itself is called (1)
(a) electrostatic force
(b) gravitational force
(c) muscular force
(d) contact force
Ans – (b) gravitational force
Q 4 – 1 kilogram weight is equal to (1)
(a) 98 N
(b) 9.8 N
(c) 0.98 N
(d) 0.098 N
Ans – (b) 9.8 N
Q 5 – A spring balance is used for measuring (1)
(a) mass
(b) weight
(c) pressure
(d) speed
Ans – (b) weight
Q 6 – Leaves fall down on the ground due to (1)
(a) electrostatic force
(b) magnetic force
(c) gravitational force
(d) muscular force
Ans – (c) gravitational force
Q 7 – When the hammer strikes the gong of an electric bell, which of the following force is responsible for the movement of a hammer? (1)
(a) Gravitational force alone
(b) Magnetic force alone
(c) Electrostatic force alone
(d) Frictional force alone
Ans – (c) Electrostatic force alone
Q 8 – During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is (1)
(a) force of gravity
(b) force of friction
(c) electrostatic force
(d) magnetic force
Ans – (c) electrostatic force
Q 9 – A ball rolling on the ground slows down and finally stops. This is because of (1)
(a) Force
(b) Less force applied
(c) Friction
(d) None of the above
Ans – (c) Friction
Q 10 – Gravity is (1)
(a) Repulsive
(b) Attraction + Repulsive force
(c) Attractive force
(d) Not a force
Ans – (c) Attractive force
Q 11 – The weight of the air that every square centimeter of any surface carries is: (1)
(a) 1 kg
(b) 10 kg
(c) 1 gm
(d) 100 kg
Ans – (a) 1 kg
Q 12 – Force of friction always acts on moving objects and its direction shall be ________. (1)
(a) On any direction
(b) Along the direction of motion
(c) Perpendicular to the direction of motion
(d) Opposite to the direction of motion
Ans – (d) Opposite to the direction of motion
Q 13 – A brick is kept in three different ways on a table as shown in the given figure. The pressure exerted by the brick on the table will be (1)
(a) maximum in position A
(b) maximum in position C
(c) maximum in position B
(d) equal in all cases
Ans –(a) maximum in position A
Q 14 – A container is filled with water as shown in the given figure. Which of the following statements is correct about the pressure of water? (1)
(a) Pressure at A > Pressure at B > Pressure at C
(b) Pressure at A = Pressure at B = Pressure at C
(c) Pressure at A < Pressure at B > Pressure at C
(d) Pressure at A < Pressure at B < Pressure at C
Ans – (d) Pressure at A < Pressure at B < Pressure at C
Force and Pressure Class 8 – Short Question Answers
Q 15 – What happens if the force is applied in the direction opposite to the motion of the body? (2)
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 16 – How nose bleeding takes place at high altitudes? (2)
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 17 – Why small heels tend to sink deep into soft sand? (2)
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 18 – Give some examples to support that the application of a force on an object may change its shape. (2)
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 the dough changes when it is rolled to make a chapati. The roller applies the force in this case.
Q 19 – Why the wall of a dam is made thicker at the bottom? (2)
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 the dam.
Q 20 – Define any two types of forces. (2)
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 noncontact 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 force is example 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 21 – Discuss the characteristics of force of gravity. (2)
Ans – Characteristics of 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 22 – Why does a car or a scooter come to rest once its engine is switched off? (2)
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.
Q 23 – Give any two examples of the gases exerting pressure. (2)
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’.
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