Cartilage is present in the joints of our body, which helps in
their smooth movement. With advancing age, this cartilage wears
off. How would this affect the movement of joints?
Is there a force of friction between the wheels of a moving train
and iron rails? If yes, name the type of friction. If an air cushion
can be introduced between the wheel and the rail, what effect
will it have on the friction?
You might have noticed that when used for a long time, slippers
with rubber soles become slippery. Explain the reason
Imagine that an object is falling through a long straight glass
tube held vertical; air has been removed completely from the
tube. The object does not touch the walls of the tube. Will the
object experience any force of friction?
Two boys are riding their bicycles on the same concrete road.
One has new tyres on his bicycle while the other has tyres that
are old and used. Which of them is more likely to skid while
moving through a patch of the road which has lubricating oil
spilled over it?
In a large commercial complex there are four ways to reach the
main road. One of the path has loose soil, the second is laid with
polished marble, the third is laid with bricks and the fourth has
gravel surface. It is raining heavily and Paheli wishes to reach
the main road. The path on which she is least likely to slip is
(a) loose soil. (c) bricks.
(b) polished marble. (d) gravel.
A boy rolls a rubber ball on a wooden surface. The ball travels a
short distance before coming to rest. To make the same ball travel
longer distance before coming to rest, he may
(a) spread a carpet on the wooden surface.
(b) cover the ball with a piece of cloth.
(c) sprinkle talcum powder on the wooden surface.
(d) sprinkle sand on the wooden surface.
Which of the following statements is incorrect?
(a) Friction acts on a ball rolling along the ground.
(b) Friction acts on a boat moving on water.
(c) Friction acts on a bicycle moving on a smooth road.
(d) Friction does not act on a ball moving through air.
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