Page 117 - Science Class 08

direc on as the bicycle rider is applying force Animals make use muscular force to carry out
to move it.
v Force can change the direc on of a moving
object.
Force is also applied to change the direc on of
a moving object. A hockey player flicks a
moving ball to change its direc on. A batsman
hits a ball to change the direc on of the ball.
v Force can change the shape of an object.
Force is also applied to change the shape of an
object. A po er applies a li le force to clay
material to change its shape in different types
of pots. When we pull a spring, its shape gets
changed.
TYPES OF FORCE
Force can be categoriesed into two main types
namely, contact force and non-contact force.
Contact Force
Contact force is the force that acts only when
two bodies are in physical contact or two
bodies interact with each other.
Contact forces are of the following types:
v Muscular Force
v Mechanical Force
v Fric onal Force
Muscular Force : It is the force exerted by the
muscles. Like when we carry the purse or bag
while moving, muscles play a great role.
For example: picking of school bags.
Muscular force is the force that is caused by
ac on of muscles inside the body. It is also
called contact force. Like we cannot push or
pull the book kept on a table without touching
it. Or bucket filled with water cannot hold
without touch. For this, we need to apply force
that will be exerted with hands. This means our
muscles play a role.
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physical tasks. Animals like bullocks, horses,
donkeys, etc. need muscular force for different
tasks.
Coolies use muscular force to li luggage.
Athletes use this muscular force for running.
Mechanical Force : It is the force exerted by
any kind of machine and obviously it needs
contact of another body due to which it is also
called as contact force.
For example, turbines in Hydel power sta on.
Fric onal Force : It is the force that opposes
the mo on of one body over the surface of
another body. It is also called contact force. We
can say that in this force, one body tries to
move on the surface of another body.
For example, wri ng anything with pen, book
lying on the table and walking on floor.
Advantages of Fric on : Fric on helps us in
walk and running. When we walk, we push the
ground with our feet, the fric on provides the
forward reac on and we move forward. If there
is no fric on between our feet and the ground,
we cannot move. In fact, we may slip. That is
why we slip on an oily surface.
Cars and other vehicles move on the road
because of fric on between the tyres and the
surface of the road. The tyres have grooves that
increase the fric on. When the grooves of the
tyres are lost over a period of me, there is a
chance of skidding the vehicle on slippery road.
Grooves
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