Page 119 - Science Class 08
P. 119
that increase fric on. These nails give them
a firm grip on the ground.
Take a wooden plank and keep it in slan ng
v The tyres of motor vehicles have grooves
posi on. Now, try to slide an object on it.
that increase to fric on. These grooves Now, spread a li le seed and slide the object
help the motor vehicles avoid skidding on again. What difference do you observe in
the road.
both the cases? Try to find out.
v The soles of the shoes are also designed in
such a way that increases the fric on.
v Some mes, the bowlers use dust to have a
firm grip on the ball. Dust increases the
fric on between the fingers and the ball so Most of the road accidents occur in the
that the ball cannot slip out of the hand. rainy season due to the skidding of the
vehicles. Therefore, we should drive slowly
v In rainy season, sand or gravel is spread on
if the road is wet.
slippery ground to increase fric on. It helps
the people walk on such slippery ground
easily.
Non-Contact Force
1. Write any two ways to minimise the
Some forces do not involve physical contact fric on.
between two bodies on which they act. These
2. Name any two lubrica ng materials.
forces act through the space between them.
Such forces are referred to as non-contact force. 3. What will happen if there are no grooves
in tyres?
Non-contact forces are of the following types:
4. Why do sportsmen wear spikes?
v Gravita onal Force v Magne c Force
5. Why sand or gravel is spread on the
v Electrosta c Force slippery ground?
Magne c Force : A magnet also has a property
1. What can you do by using force? which enables it to a ract the objects made of
2. Give an example that force can change iron. This force of a rac on of a magnet is
the shape of an object. called magne c force. Large magnets are used
to li big iron pieces.
3. What do you mean by non-contact force?
4. Write any two disadvantages of fric on. The magne c property of lodestone has been
known since ancient mes. Similarly, the use of
Gravita onal Force a magne c compass has been in vogue for a
All objects fall on the earth’s surface, it is very long me. Its needle, which is a small
because our earth a racts all the things magnet, is acted upon by the magne c field of
towards it. The force of a rac on exerted by the earth. This is an instance of the magne c
our earth is called the gravita onal force. It is force in ac on.
the example of non-contact force which acts on Similarly, when a piece of magnet is placed
all the things all the me. It is, therefore, things near iron nails, these nails are a racted
fall down and do not go upward. towards the magnet by a magne c force.
Science-8 119
