FRICTION

While travelling on a rickshaw, you might have experienced that
if the seat cover is very smooth, you tend to slip when brakes are
applied suddenly. Explain.

We have two identical metal sheets. One of them is rubbed with
sand paper and the other with ordinary paper. The one rubbed
with sand paper shines more than the other. Give reason.

When the cutting edge of a knife is put against a fast rotating
stone to sharpen it, sparks are seen to fly. Explain the reason.

A father and son pushed their car to bring it to the side of road
as it had stalled in the middle of the road. They experienced that
although they had to push with all their might initially to move
the car, the push required to keep the car rolling was smaller,
once the car started rolling. Explain.

A marble is allowed to roll down an inclined plane from a fixed
height. At the foot of the inclined plane, it moves on a horizontal
surface (a) covered with silk cloth (b) covered with a layer of sand
and (c) covered with a glass sheet. On which surface will the
marble move the shortest distance. Give reason for your answer.

Explain why the surface of mortar and pestle (silbatta) used for
grinding is etched again after prolonged use?

The handle of a cricket bat or a badminton racquet is usually
rough. Explain the reason.

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?

Yo u 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?

Will force of friction come into play when a rain drop rolls down
a glass window pane?

Explain why objects moving in fluids must have special shapes.

Give examples to show that friction is both a friend and a foe.

Explain why sliding friction is less than static friction.

Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Explain why sportsmen use shoes with spikes.

You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?

Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing orderwill be

(a) wet marble floor, dry marble floor, newspaper and towel.

(b) newspaper, towel, dry marble floor, wet marble floor.

(c) towel, newspaper, dry marble floor, wet marble floor

(d) wet marble floor, dry marble floor, towel, newspaper

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

(a) rolling, static, sliding

(b) rolling, sliding, static

(c) static, sliding, rolling

(d) sliding, static, rolling

Fill in the blanks.

(a) Friction opposes the ________between the surfaces in contact with each other.

(b) Friction depends on the _________of surfaces.

(c) Friction produces _________.

(d) Sprinkling of powder on the carrom board ________friction.

(e) Sliding friction is ________than the static friction.