Transcript Ch_3 Presentation

Chapter 3
Newton’s Inertia
(Friction Included)
Friction
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µ is the greek letter “mu” and is the
commonly used symbol/variable that
represents friction.
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But what is Friction and why does it occur?
Discuss....
Friction
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Friction is the force that acts between
materials as they move past each other.
Friction is created from the irregularities and
differences in materials. Even very smooth
surfaces have some microscopic
ridges/grooves. These, clash with the
opposite surface, and produce opposing
forces.
The Perspective
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https://www.youtube.com/watch?t=70&v=Iq2
BII29oKM
Friction often times works to slow down
objects, as without it objects that interact at
parallel angles would not affect each other.
Friction Produces Heat.
F=ma
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In the same light that weight works as a function of
Gravity.( W=mgh)
Friction is included in Acceleration when trying to
obtain the force of a system or object.
When conditions are ideal, we ignore friction. In
general we only ignore friction when learning
elementary physics.
Friction is very important!
F_frict= µ X F_norm
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http://www.physicsclassroom.com/class/newtl
aws/Lesson-3/Finding-Acceleration
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Please Practice these problems.
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Show Friction vs Applied force in Jenga.
Inertia and Newton
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A ball rolls down and endless/frictionless
surface. It rolls until the end of time.
An object that is not affected by any outside
forces will keep on keeping on, this is based
on an innate property of matter called inertia.
By your book: Inertia is the property of a
body to resist change to its state of
motion.
Newton’s First
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Also called Law of Inertia; Objects at rest will
stay at rest. Objects at uniform speed will
remain at uniform motion. Unless these
objects are affected by a non-zero net force.
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Simply Put, objects continue to move by
themselves unless stopped. Only an initial
applied force is necessary to accelerate the
object, but not to maintain motion.
Mass- Measure of Inertia
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The More mass, the more Inertia.
Thus, the heavier an object the more inertia it
has and the greater the force it takes to slow
that object down.
Mass and Inertia have a directly proportional
relationship.
Mass vs Weight
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Mass and Weight are not the same thing...
Once again; mass is the amount of matter an
object is composed of. Weight is the effect
gravity has on an objects mass.
If the Moon is said to have 1/5th the gravity of
Earth, than what would be the weight of a
500lb object on the surface of the moon?
Would the objects mass stay the same or
would it change like the weight did?
Answer
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A 500 lbs object on earth would weigh 100
lbs on the moon.
The mass of the object would not change, as
the object still has the same amount of
matter within it.
If we however were to change the amount of
mass inside the object by adding matter to it,
than the weight of the object would increase.
Mass in Kilograms
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Mass is measured in Kilograms.
An object that has a 1 kg mass is also said to
have about 10 Newtons of Force or 2.25 lbs
of weight.
Mass, Volume and Density
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Density allows us to analyze why a pillow is much
larger than a red brick, yet weighs much less.
Density is how much matter is distributed over the
amount of space an object covers.
The formula D= m/v ; explains the relationship.
A pillow has mass(matter) spread out over a larger
volume. It also has less matter than the brick.
A brick has more mass compacted into a small
volume, thus feeling heavier than the pillow...
Can you think of some more examples?
Some Equations
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So far we know F= force (N),
F= ma, where m is mass and a is
acceleration.
µ is friction and F_friction= µ X F_n
Weight = MgH or just Mg
Density= Mass/Volume
F_net= F1+F2+F3......