1. Science PPT
Topic:-Friction[Physics]
Name:-Nihar.sanjeev.satpute
standard:-9th

2. Friction[introduction]
Friction is a force that opposes the relative motion
between two surfaces of objects in contact. The force of
friction always acts in a direction opposite to that of the
applied force. Friction exists between two surfaces due
to irregularities on the surfaces of the objects in contact,
interlocking of micro-level irregularities of the two
surfaces and ploughing of harder surfaces into smoother
surfaces.

3. Factors That Affect Friction
• Roughness of the surface
• the extent to which the two surfaces press
together
• Nature of the surface

4. Types of Friction
There are three types of friction that exist between solid surfaces.
They are static friction, sliding friction and rolling friction.
Frictional force that comes into action before the start of the
motion of an object is called static friction. Example: a box
placed on the floor. When an object slides over another surface,
the frictional force that comes into action is sliding friction.
Example: a boy sliding on a slide. The frictional force exerted
when an object rolls over a surface is called rolling friction.
Example: rolling ball on the ground. It is found that:
Rolling friction < sliding friction < static friction.
The frictional force exerted by fluids when objects move through
them is called fluid friction or drag.

5. There are four types of friction
static friction sliding friction
rolling friction Fluid friction

6. Four types of friction and their
definition
 Static friction:-when a force is applied to an object
but it does not cause it to move
example: pushing on a wall
 Fluid friction:-occurs when a object moves through a
fluid, meaning either a liquid or gas
examples: skydiving, swimming
 Sliding friction:-occurs when solid surfaces slide
over each other
example:-falling on the pavement
 Rolling friction:-occurs when solid surfaces slide
over each other
example:-falling on the pavement

7. Effects of Friction
 Friction produces heat.
 Friction causes wear and tear.
 Friction opposes motion

8. Advantages of Friction
 Friction between pen and paper enables us to write on
the paper.
 Friction between our feet and the ground allows our
movements like standing, walking and running
 Friction between the surface of the road and tyres of our
vehicles allow the vehicles to move without slipping

9. Disadvantages of Friction
 Friction causes moving objects to stop or slow
down.
 Friction produces heat causing wastage of
energy in machines
 Friction causes wear and tear of moving parts of
macinery, soles of shoes, etc

10. Methods of Increasing and Reducing
Friction
In real life, there are circumstances where we have to
increase the friction and minimize the friction. Friction
can be increased by increasing the roughness of the
surfaces in contact. For example, treading of shoes and
tyres is done to increase friction. When friction is
undesirable we have to reduce the friction. Friction can
be minimized by using lubricants like oil and grease and
by using ball bearing between machine parts. A
substance that is introduced between two surfaces in
contact, to reduce friction, is called a lubricant. Fluid
friction can be minimized by giving suitable shapes to
the objects moving in the fluids.

11. Friction Is A Necessary Evil
There are instances in daily life where friction is a
necessity. For example, without friction, we cannot hold
objects in our hands; we cannot walk and cannot light a
match stick. Sometimes friction is not desirable, for
example friction between machinery parts, which
causes wear and tear. As friction is advantageous to us it
is considered as a friend but due to its disadvantages it is
a foe. Depending on the circumstance, friction can be a
help or a hindrance. Thus it is a necessary evil.