Friction is the force that resists the motion or sliding of objects in contact. There are four main types of friction: rolling friction occurs between surfaces in rolling motion like wheels; static friction acts on objects at rest; sliding friction acts on objects moving over each other like a pencil on paper; and fluid friction is the resistance of liquids and gases on objects moving through them like air or water resistance. Friction can be reduced by smoothing surfaces, replacing rolling with sliding motion, or adding lubricants.

1. Types of Friction

2. What is Friction?
 Friction is the resistance to the sliding,
rolling, or flowing motion of an object
due to its contact with another object.
 When a moving object comes in contact
with another object, friction is the
opposing force that slows or stops the
moving object.

3.  Without friction, an object would continue to move at
constant speed forever.
 The strength of the force of friction depends on the
type of surfaces and how hard the surfaces push
together.
 Rough surfaces produce greater friction than smooth
surfaces.

4.  Without friction you could not
 Write
 Drive a car
 Fly an airplane
 Why not?

5. Four Types of Friction
 Rolling Friction
 Static
 Sliding Friction
 Fluid Friction

6. What do all these things have in common?

7. Rolling Friction
 Rolling friction is friction
that occurs between surfaces
in motion in which one of
the surfaces is a wheel,
roller, or ball.
 Examples:
 Riding a bike – tires and ground
 Bowling – ball and lane

8. What do all these things have in common?

9. Static Friction
 Static friction is friction
that occurs when the
surfaces in contact are at
rest (not in motion).
 Examples:
 A book resting on a desk.
 A potted plant sitting on a
sidewalk.

10. What do all these objects have in common?

11. Sliding Friction
 Sliding friction is
friction that occurs
when solid surfaces
slide over one another.
 Examples:
 Writing – pencil point and
paper
 Combing your hair –
surface of comb and
strands of hair

12. What do all these things have in common?

13. Fluid Friction
 The force that tries to slow objects down when they
move through a liquid or a gas. It's also known as
"drag", or "air resistance".
 All gases and liquids are fluids.
 An airplane and a swimmer both experience fluid
friction.

14. Ways to Reduce Friction
 Smooth the surface
 Replace rolling with sliding
 Add oil or another type of lubricant

15. Friction Song
 What is friction?
 Friction Video

16. Gravity and Free Fall
 An object is in free fall when the only
force acting on the object is gravity.
 Free-falling objects do not encounter
air resistance.
 In free fall, the force of gravity is an
unbalanced force.

17. Calculating Free Fall
All objects in free fall accelerate at the same rate –
9.8 m/s² - regardless of their mass.
in one second = 9.8 m/s²
in two seconds = 19.6 m/s²
in three seconds = 29.4 m/s²
in four seconds = ________
The velocity continues to increase as the object
falls.

18. Gravity, Free Fall, and Projectile Motion
 An object that is thrown is called a projectile.
 If there is no air resistance, an object that is dropped
and an object that is thrown are both in free fall.
 Without the force of air resistance, both objects will
hit the ground at the same time.

19. Gravity and Air Resistance
 Most objects falling through air
experience a type of fluid friction called
air resistance.
 Air resistance is not the same for all
objects.
 The greater the surface area of the
object the greater the air resistance.
 However, since the elephant has more
mass, it has more downward force of
gravity and falls faster.

20. What type of friction?

21.  Static Friction

22. What type of friction?

23.  Rolling Friction

24. What type of friction?

25.  Fluid Friction

26. What type of friction?

27.  Static Friction

28. What type of friction?

29.  Sliding Friction

30. What type of friction?

31.  Fluid Friction