3. Suppose you decide to ride a skate board
You push off the ground and start moving
According to Newton’s second law
of motion ,if no
other forces are acting
on your skateboard , you
will continue to move….BUT
4. The reason is that there exist a force
between the
ground and lower portion of the
skateboard, called
FRICTIONAL FORCE.
5. Friction is the force which opposes relative motion
between two surfaces in contact with each other
6. Even though a surface may look smooth, if you magnify the
surface it isn’t smooth.
Everything is made of molecules. The molecules come
together to make bumps. Some surfaces have molecules that
leaves large bumps and some leaves small bumps.
Micro welds occur when two bumpy surfaces are rubbed up
against each other they stick together.
7. Static friction
Frictional force between two surfaces before there is
a relative force between the surfaces in contact.
Kinetic friction
It is the force of friction which calls in to play when
there is relative force between the surfaces.
8. Rolling friction
Rolling friction between two surfaces in contact is the force of friction which
calls into play when a body rolls over another.
Sliding friction
sliding friction is the force that opposes the motion of two surfaces sliding
past each other.
9. Helps us in walking conveniently. It save us from
slipping.
Helps us in writing on piece of paper.
Helpful in eating and drinking
Lighting a match stick by rubbing.
Nails and screws join two surfaces due to the
friction.
we can not climb a tree.
Trains can run on the rails.
In fact life become impossible if there is no friction
in nature.
10. Due to friction the whole energy given to a machine is
not converted in to useful work; a portion of energy is
wasted to overcome friction.This reduces the
efficiency of the machine. The energy used in
overcoming friction appears as heat. Moreover, friction
causes wear and tear of the moving parts of the
machine due to rubbing.
12. It is not possible to walk or drive through muddy
and slippery roads. For this sand and gravels are
spread to reduce friction
Tyres of our vehicles also the soles of the shoes are
grooved.
Mountaineers also wear spiked shoe.
To overcome skidding along a slippery surface we adopt
measures to increase friction.
13. •Reduce the area of contact of two surfaces.
•Making the surfaces as smooth.
•Lubrication can reduce friction.
•Using ball bearings.
