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 Friction
Sliding Friction
Fluid Friction
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
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.
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
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
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.
