FRICTION
A force that
opposes motion
Objectives…
Explain why friction occurs.
 List the two types of friction, and give
examples of each type.
 Explain how friction can be both
harmful and helpful.

What is friction?

Is a force that opposes
motion between two
surfaces that are in
contact
When does friction occur?
 Friction
occurs when
two surfaces
are in
contact
Also…

When a
liquid or
gas is
pushed out
of the way
of a moving
object
Why does friction occur?

Because the hills and valleys of a
surface are in contact with the hills
and valleys of other surfaces, this
produce friction.
Friction depends on…
Roughness of surfaces and
 Force that objects are
being pressed one against
the other; or their weights

What increases friction?
Rough surfaces
And weight of objects

What does the amount of friction
on surfaces depend on?
 the
amount of friction depends on
how well the surfaces grip each
other.
Tyres on a road have very high
friction (they don't slip),
skates on ice have very low
friction (they slip easily).
In a liquid or a gas
 For
a solid object moving through
a liquid or gas,
the amount of friction depends on
the shape and surface area of the
object
and the viscosity (thickness or
thinness) of the liquid.
TYPES OF FRICTION
KINETIC AND
STATIC

What is kinetic friction?
It is the friction
between two moving
surfaces

Sliding and Rolling
Static friction

It occurs when a force is
applied to an object but this
object doesn’t move.
Static friction
Is friction good or bad?

Friction can be good.
When we walk we push
backwards against the
ground,
the opposing force pushes us
forwards.
Without friction our feet
would slip and walking
would be impossible.
It is also good
 To
stop
your
bicycle
(brake
system)
But sometimes is bad…
Soil erosion caused by wind (friction
of a fluid).
 Holes in your shoes, jeans. (friction of
a solid) high friction
 Lack of friction is dangerous too, you
may fall if the floor is very slippy.

Some ways to reduce friction
Some ways to increase
friction
GO TO THIS LINK TO INCREASE YOUR
KNOWLEDGE ABOUT FRICTION

http://www.gcsescience.com/pfm32.htm