To
control the speed of car is an important issue for a safe journey. We travel in
a car to
meet
the necessity of our daily lives. We use different vehicles during the journey.
Sometimes
in bus or train or we use personal vehicles. The speed of a vehicle and force
is
inseparably related to each other during the journey in such vehicles. The
speed of a
car
plays a vital role for a safe journey. The speed or velocity would not be such
that
which
is not controllable. To travel in a distant destination, it is necessary to
know about
The
driver has to check the car well before start journey. As an example, whether
the
tyre
or brake is perfectly right or not. He has to ensure whether the engine, used
battery,
front
and rear lamps, wiper, and signal lights of two sides are right and properly
working.
In addition, he has to properly adjust the mirrors used in the car.
At
first the driver and the passengers will wear the seat belt during driving
time. It is
observed
that most of the road accidents occur due to very fast driving. So, the driver
must
be cautious to control the speed of the car. The kinetic energy becomes more
due to
increased
speed. For example- if the velocity of the car is doubled, its kinetic energy
is
increased
by four times in comparison to that of the earlier value. If the velocity is
increased
by three times, kinetic energy is increased by nine times. Then it becomes
difficult
to reduce or to control the velocity and the accident becomes terrible.
Drivers
are advised to choose a vehicle which they are used to driving earlier. It is
not
wise
to try to drive a new vehicle suddenly. It is observed that the youth try to
drive a
new
car emotionally. It’s not proper at all. Slow down the vehicle’s speed when you
meet
other vehicles from opposite direction. To obey the traffic sign and traffic
law is
the
citizen responsibility of the vehicle driver. The driver should concentrate on
driving
absolutely
during driving.
3.9 Friction and force of friction
We
are familiar with friction in various ways in our daily lives. From Newton’s
first law
of
motion we know that if no force acts on a body the body will continue in its
state of
rest
or of uniform motion in a straight line. Does it actually happen in reality?
Take a
marble
and roll it on the floor. When you roll the marble, you apply a force on it. As
a
result,
the marble becomes mobile on the ground. According to Newton’s law the marble
should
remain in uniform velocity. In practice, it is seen that the marble comes to
rest
after
traversing a small distance. This happens due to the friction of the floor.
When the
marble
is in motion on the floor, a frictional force is developed due to the mutual
friction
between
the marble and the floor. This force acts in the direction opposite to the motion
and
hinders the motion. If the friction of the floor was absent, then the marble
would
continue
its perpetual motion with uniform velocity.
When
a body moves or tends to move over another body, then a resistance is developed
between
the two surfaces in contact, which is known as friction. This resistive force
is
called
frictional force.
Physics
61
The
frictional force always acts opposite to the motion and obstructs the motion.
Origin of friction
Whenever
the surface of an object slides over the surface of another object, each object
exerts
a frictional force on the other. The question arises- why friction occur?
Friction is
the
result of the surface irregularities of any two surfaces. Each object has a
surface.
Again,
the surface may be smooth or rough. Apparently, the surface of an object seems
to
be smooth, but it is observed that there are high and low grooves on it when
viewed
by
a microscope [Figure 3.8]. When an object moves on another object, then the
grooves
of
the two surfaces in contact catch onto one another. As a result of which the
motion of
one
surface over another surface gets obstacled.
As
the grooves of a surface deepend and their number increases i.e. as the surface
become
rougher, the motion of one surface over another becomes more obstructed. Then
the
magnitude of frictional force also increases. The body becomes mobile if it can
overcome
the resistance of the surface in contact. The frictional force causes the
object
to
slow down and stop thereby.
Figure:
3.8
Types of friction
Generally
there are four types of friction.
1.
Static friction
2.
Sliding friction
3.
Rolling friction
4.
Fluid friction
Static friction
Static
friction is the friction between two surfaces that aren't moving relatively to
each
other.
When
a force is applied to an object, but it does not cause it to move, then static
friction
works.
When a massive body on a floor is pulled by a force but it does not move, then
the
frictional force created is called force of static friction. The static
frictional force is
developed
opposite to the applied force and acts until motion is produced.
When
two bodies at rest are in contact with one another and one body is made to move
on
the other body, the friction produced between them until a relative motion is
created
is
called static friction.
62
Physics
Sliding friction
Sliding
friction is friction where an object slides, or rubs against, another surface.
We
fall down and traverse a small distance when we move in a slippery road. When a
hard
brake is applied on a car moving fast, the car does not stop rather cross a
small
distance
by sliding.
Rolling friction
Rolling
friction is friction between a rolling object and the surface that it is
rolling on.
The
wheel’s motion of a cycle, motion of marble is example of rolling friction.
During
travelling
we use luggage carrier having wheels to carry goods. If there was no wheel in
the
luggage carrier then it was too difficult to pull it by sliding from one place
to
another.
Due to the attachment of wheel it becomes easier to pull it i.e. the force of
rolling
friction is less than that of the static friction.
Fluid friction
When
an object moves in a fluid i.e. a liquid or gas, the friction acts is called
fluid
friction.
We
have to overcome a barrier in water while swimming in the pond. This barrier is
the
fluid
friction. A parachute works by harnessing the air resistance. The air
resistance is a
type
of frictional force which works against the force of gravity of the earth. As
an open
parachute
has a large surface area, it helps provide enough air resistance. As a result,
the
sky-diver’s
falling speed is decreased mostly. So, the skydiver will then be able to
descend
slowly and safely.
3.10 Effects of friction on motion
Friction
has enormous influence on the motion of an object. Friction is
a
kind of resistive force which slows down the motion of a body.
Though
friction creates many problems in our daily lives, it plays a
vital
role for movement and vehicle operaration. In this section we
shall
discuss about tyre’s surface, smoothness of road and role of
friction
for controlling motion.
Tyre’s surface
Driving
vehicles is possible because of the friction between the tyres and the road
surface.
The friction force between the tyres and the road depends on condition of the
tyres
and surface of the road. It also depends on the weight of the vehicle. The
tyre’s
rubber
surface is designed with treads i.e. grooves or teeth. The tyre surface is up
and
down
due to these grooves. If the tyre is new, these grooves are distinct; as a
result the
force
of friction between the tyre and the road is maximum. When the tyre becomes
old,
Figure:
3.9
Physics
63
their
grooves are worn out and the surface becomes flat. As a result the frictional
force
between
the tyre and the road decreased mostly. Say, what inconvenience may arise due
to this.
