Friction and Types of Friction

2. • Friction is a force between two surfaces
that are sliding, or trying to slide across one
another, for example when you try to push a
toy car along the floor.
• Friction always works in the direction
opposite from the direction the object is
moving, or trying to move. It always slows
a moving object down.
Moving
Friction

3. • The amount of friction depends on the materials
from which the two surfaces are made. The
rougher the surface, the more friction is
produced. For example, you would have to push a
book harder to get it moving on a carpet than you
would on a wooden floor. This is because there is
more friction between the carpet and the book
than there is between the wood and the book.

4. • Friction also produces heat.
For example, if you rub your
hands together quickly, they get
warmer.

5. • Friction can be a useful force because
it prevents our shoes slipping on the
pavement when we walk and stops car
tyres skidding on the road.

6. • Ice causes very little friction, which is
why it is easy to slip over on an icy day.
But this is a good thing for ice skating and
sledging.

7. • Sometimes we want to reduce friction. For
example, moving parts inside a car engine are
lubricated with oil, to reduce friction between
them. The oil holds the surfaces apart, and can
flow between them. The reduced friction means
there is less wear on the metal, and less heat
produced.

8. • Friction can also be reduced with the use of
ball bearings or roller bearings.

9. • Air resistance is a type of friction between
air and another material. When an aeroplane
flies through the air, for example, air
particles hit the aeroplane, making it more
difficult for the aeroplane to move through
the air.

10. • Some shapes, known as streamlined
shapes, cause less air resistance than
others. Aeroplanes and cars are
streamlined, so that they move through the
air as easily as possible.

11. Static Friction – the frictional force
present just before motion begins.
Starting Friction is when Static Friction is
at is maximum.
Kinetic Friction – the frictional force
present with motion
Note: Static Friction is usually higher
than Kinetic Friction

12. • Static Friction is usually higher than
Kinetic Friction because it is harder
to get something started than it is to
keep it going.
• Friction is practically independent of
the area of contact

13. The Coefficient of Friction
Frictional Force, both static and kinetic, is
directly proportional to the force pressing
the two surfaces together. The more
weight, the more friction.
normal
(kinetic)friction
kinetic
normal
(static)friction
static
normalfriction
F
F
F
F
FF
==
=
µµ
µ
normalfriction FF ∝
The missing link to the above equation is the
Coefficient of Friction, or μ:

14. Synthesis:
• How does friction affect the motion of
an object?
• Compare and Contrast: Compare and
contrast the types of friction that we
have learned using a Venn diagram.

15. Assignment:
• Journal Notebook:
Friction Forever Journal
Keep a journal tracking all the activities
that you perform in one day (you will
start tomorrow), where friction plays a
role. Justify how friction plays a role in
the activity.

16. Quiz