Q51. Give two examples of situations in which applied force
causes a change in the shape of an object.
Ans. Two examples in which applied force causes a
change in the shape of an object are:
The shape of dough changes on pressing with
rolling pin to make chapatis.
The shape of a toothpaste tube changes when
we squeeze it.
Q52. What are the various effects of force?
of force are:
make an object move from rest.
change the speed of an object if it is moving.
change the direction of motion of an object.
bring about a change in the shape of an object.
Q53. Why a fountain of water is created at the leaking joints or
holes of pipes of the main water supply line?
times we see a fountain of water rushing out of the leaking joints (or holes)
in the pipes of main water supply line. It is due to the very high pressure
exerted by water on the sides (or walls) of the pipes that such a fountain of
water is formed.
Q54. Why does the liquid rise in a syringe when its piston is
How does a liquid medicine enter a syringe?
the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the
pressure inside the syringe is lowered. The greater atmospheric pressure acting
on the surface of the liquid pushes the liquid up into the syringe.
Q55. Why nose bleeding occurs at high altitudes?
Why do mountaineers suffer from nose bleeding at high altitudes?
high altitudes, the atmospheric pressure becomes much less than our blood
pressure. Since, our blood is at higher pressure than outside pressure,
therefore, some of the blood vessels in our body burst and nose bleeding takes
place at high altitudes.
Q56. Does application of a force would always result in a change
in the state of motion of the object?
Ans. No. Many a time application of force does not
result in a change in the state of motion. For example, a heavy box may not
move at all even if you apply the maximum force that you can exert. Again, no
effect of force is observed when you try to push a wall.
Q57. Name the forces acting on a plastic bucket containing water
held above ground level in your hand. Discuss why the forces acting on the
bucket do not bring a change in its state of motion.
Ans. In this case, muscular force is acting in upward
direction and the force of gravity is acting in downward direction. The two
forces are equal in magnitude but opposite in direction. Therefore, the net
force on the bucket is zero. Hence, there is no change in its state of motion.
Q58. Why atmospheric pressure decreases as we go higher up above
the earth's surface?
Ans. The pressure at any level in the atmosphere may
be interpreted as the total weight of the air above a unit area at any
elevation. Since most of the atmosphere's molecules are held close
to the earth's surface by the force of gravity, air pressure decreases as we go
higher up above the earth's surface.
Q59. What happens when a charged plastic straw is brought near another
uncharged plastic straw?
Ans. A straw is said to have acquired electrostatic
charge after it has been rubbed with a sheet of paper. Such a straw is an
example of a charged body. A straw rubbed with paper attracts another
straw but repels it if it has also been rubbed with a sheet of paper.
Q60. Why does a plastic comb rubbed with dry hair attract tiny
pieces of paper?
a plastic comb is rubbed in dry hair, the comb gets electric charges by
friction. And when this electrically charged comb is brought near tiny pieces
of paper, it exerts an electrostatic force of attraction on them. Due to this
electrostatic force, the tiny pieces of paper move towards the comb and stick
Q61. What is meant by saying that force is due to interaction?
Ans. Example: Suppose a man is standing
behind a stationary car. The car will not move just due to his presence.
Suppose the man now begins to push the car, that is, he applies a force on it.
The car may begin to move in the direction of the applied force.
From the above example, we can infer that at
least two objects must interact for a force to come into play.