Chapter 8 Motion

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Chapter 8 Motion
8. Mass 9. Second Law of Motion 10. Mass and
Weight 11. Third Law of Motion 12. Circular
Motion 13. Newton's Law of Gravity 14.
Artificial Satellites
1. Speed 2. Vectors 3. Acceleration 4. Distance,
Time, and Acceleration 5. Free Fall
System6. Air Resistance7. First Law of Motion
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1. Speed

• Definitions
• Speed
• The rate at which something moves a given
  distance.
• Faster speeds greater distances
• General formula for speed
• Speed distance / time
• Abbreviations commonly used
• d distance t time v speed
• v d/t

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1. Speed
Velocity
Distance
Time
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1. Speed
Average speed is the total distance traveled by
an object divided by the time taken to travel
that distance.  Instantaneous speed is an
object's speed at a given instant of time.
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2. Vectors
Magnitude of a quantity tells how large the
quantity is. Scalar quantities have magnitude
only. Vector quantities have both magnitude and
direction.
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2. Vectors
Velocity is a vector quantity that includes both
speed and direction.
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Velocity Example
You are watching someone split wood with a sledge
hammer a wedge. When watching, you notice that
it takes 3 seconds for you to hear the sound
after you see the sledge strike the wedge. Given
that sound travels at 330 m/s at that
temperature, find the distance from the wood
splitter to you.
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3. Acceleration
Acceleration of an object is the rate of change
of its velocity and is a vector quantity. For
straight-line motion, average acceleration is the
rate of change of speed
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2-3. Acceleration
3 Types of Acceleartion
Speeding Up Slowing Down Turning
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2- 4. Distance, Time and Acceleration
(V1 V2) Vavg 2
(20mph 60mph)
40mph 2
d vavg t d ½at2
30mph 2hr 60miles ½ 10m/s/s 52 125m
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2-5. Free Fall
The acceleration of gravity (g) for objects in
free fall at the earth's surface is 9.8 m/s2.
Galileo found that all things fall at the same
rate.
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2-5. Free Fall
The rate of falling increases by 9.8 m/s every
second.
Height ½ gt2 For example
½ (9.8 )12 4.9 m½(9.8)22 19.6 m ½ (9.8)32
44.1 m ½ (9.8)42 78.4 m
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2-5. Free Fall
A ball thrown horizontally will fall at the same
rate as a ball dropped directly.
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2-5. Free Fall
A ball thrown into the air will slow down, stop,
and then begin to fall with the acceleration due
to gravity. When it passes the thrower, it will
be traveling at the same rate at which it was
thrown.
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2-5. Free Fall
An object thrown upward at an angle to the ground
follows a curved path called a parabola.
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2-6. Air Resistance

• In air
• A stone falls faster than a feather
• Air resistance affects stone less
• In a vacuum
• A stone and a feather will fall at the same speed.

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2-6. Air Resistance

• Free Fall
• A person in free fall reaches a terminal velocity
  of around 54 m/s
• With a parachute, terminal velocity is only 6.3
  m/s
• Allows a safe landing

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2-6. Air Resistance

• Ideal angle for a projectile
• In a vacuum, maximum distance is at an angle of
  45o
• With air resistance (real world), angle is less
• Baseball will go furthest hit at an angle of
  around 40o

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2-7. First Law of Motion
The first law of motion states If no net force
acts on it, an object at rest remains at rest and
an object in motion remains in motion at a
constant velocity.
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Foucault Pendulum
Inertia keeps a pendulum swinging in the same
direction regardless of the motion of the earth.
This can be used to measure the motion of the
earth. As the Foucault Pendulum swings it
appears to be rotating, but it is the earth that
is rotating under it. To the right is the
Foucault Pendulum at the Pantheon in Paris,
France.
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Foucault Pendulum
Other Web sites that illustrate the Foucault
Pendulum.
http//en.wikipedia.org/wiki/FileFoucault-rotz.gi
f http//www.physclips.unsw.edu.au/jw/foucault_pen
dulum.html http//aspire.cosmic-ray.org/labs/scien
tific_method/pendulum.swf http//www.calacademy.or
g/products/pendulum/page7.htm http//www.youtube.c
om/watch?vnB2SXLYwKkM
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2-8. Mass
Inertia is the apparent resistance an object
offers to any change in its state of rest or
motion.
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2-9. Second Law of Motion
Newton's second law of motion states The net
force on an object equals the product of the mass
and the acceleration of the object. The direction
of the force is the same as that of the
acceleration.
F Ma
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2-9. Second Law of Motion
A force is any influence that can cause an object
to be accelerated.
The pound (lb) is the unit of force in the
British system of measurement 1 lb 4.45 N (1 N
0.225 lb)
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2-10. Mass and Weight

• Weight
• Definition The force with which an object is
  attracted by the earths gravitational pull
• Example A person weighing 160 lbs is being
  pulled towards the earth with a force of 160 lbs
  (712 N).
• Near the earths surface, weight and mass are
  essentially the same

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2-11. Third Law of Motion
The third law of motion states When one object
exerts a force on a second object, the second
object exerts an equal force in the opposite
direction on the first object.
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2-11. Third Law of Motion
Examples of the 3rd Law
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2-12. Circular Motion
Centripetal force is the inward force exerted on
an object to keep it moving in a curved path.
Centrifugal force is the outward force exerted
on the object that makes it want to fly off into
space.
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2-12. Circular Motion
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2-12. Circular Motion
833 N is needed to make this turn. If he goes too
fast, which wheels are likely to come off the
ground first?
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2-13. Newton's Law of Gravity
G 6.67 x 10-11 Nm/kg2
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2-13. Newton's Law of Gravity

• How can we determine the mass of the earth using
  an apple?
• This illustrates the way scientists can use
  indirect methods to perform seemingly impossible
  tasks

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2-13. Newton's Law of Gravity

• How can we determine the mass of the earth using
  an apple?
• This illustrates the way scientists can use
  indirect methods to perform seemingly impossible
  tasks

mg
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2-15. Artificial Satellites

• The world's first artificial satellite was
  Sputnik I, launched in 1957 by the Soviet Union.

GPS-Global Positioning Satellite
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2-15. Artificial Satellites
The escape speed is the speed required by an
object to leave the gravitational influence of an
astronomical body for earth this speed is about
40,000 km/h.
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2-15. Artificial Satellites
The escape speed is the speed required by an
object to leave the gravitational influence of an
astronomical body for earth this speed is about
40,000 km/h.