CHAPTER 3 ACCELERATED MOTION

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CHAPTER 3 ACCELERATED MOTION

•  
• In this chapter you will
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•  Develop descriptions of accelerated motions.
• Use graphs and equations to solve problems
  involving moving objects.
• Describe the motion of objects in free fall.

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CHAPTER 3 SECTIONS

• Section 3.1 Acceleration
• Section 3.2 Motion with Constant Acceleration
• Section 3.3 Free Fall

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SECTION 3.1 ACCELERATION

• Objectives
• Define acceleration.
• Relate velocity and acceleration to the motion of
  an object.
• Create velocity-time graphs.

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INTRO/CHANGING VELOCITY

• In this chapter we will be presented with
  situations in which the velocity of an object
  changes, while the objects motion is still along
  a straight line.
• The most important thing to notice in these
  motion diagrams is the distance between
  successive positions.
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• If an object speeds up each subsequent velocity
  vector is longer.
• If an object slows down each subsequent velocity
  vector is shorter.

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VELOCITY TIME GRAPHS

• Velocity Time Graph a graph that can be used to
  plot the velocity of an object versus the time
  and it determines the sign of the objects
  acceleration.
• The area under the curve of a Velocity Time graph
  is the DISPLACEMENT.
• The slope is the ACCELERATION.
• The rate at which the cars velocity is changing
  can be found by calculating the slope of the
  velocity time graph.
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• Acceleration the rate at which an objects
  velocity changes. It is the velocity of an
  object divided by the time interval. It is
  measured in m/s2. It is the slope of a Velocity
  Time Graph.
• a v/t

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AVERAGE INSTANTANEOUS ACCELERATION

• Average Acceleration the change in velocity
  divided by that time interval. It is a vector
  quantity. It is measured in m/s2.
• ?a vf vi ?v Average Acceleration
  Equation
• tf ti ?t
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• When the velocity increases its change is
  positive and the Acceleration is Positive.
• When the velocity decreases its change is
  Negative and so is the Acceleration.
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• Instantaneous Acceleration the change in an
  objects velocity at a specific instant in time.
  It is the slope of the tangent line at a specific
  instant of time.

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DISPLAYING ACCELERATION ON A MOTION DIAGRAM

• Example 1 p. 60
• Velocity the runners velocity increased from 0
  to 10 m/s in 4 s and then it almost levels off
  but slightly increases from 4 to 10 s.
• Acceleration the runner accelerates in the first
  4 s and then runs with almost a constant speed
  from 4 to 10 s.
• Also a Rise / Run (11 2.8) / (2.4 0)
  8.2 / 2.4 a 3.42 m/s2
• And a Rise / Run (10.3 10) / (10 0) .3
  / 10 a .03 m/s2
• Do Practice Problems p. 61 1-5

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POSITIVE AND NEGATIVE ACCELERATION

• In other words, when the objects acceleration is
  in the same direction as its velocity, the
  objects speed increases. When they are in
  opposite directions the speed decreases.
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• Both the direction of an objects velocity and
  its direction of acceleration are needed to
  determine whether it is speeding up or slowing
  down.
• The sign of acceleration does not indicate
  whether the object is speeding up or slowing down.

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DETERMINING ACCELERATION FROM A V-T GRAPH

• Go Over Figure 3.8
• ?a vf vi ?v
• tf ti ?t
•   
• Do Example Problem 2 p. 63
• ?a vf vi ?v
• tf ti ?t
• ?a (0 2.5) / (5 0) -2.5 / 5 - .5
  m/s2
• So the sign is NEGATIVE as it rolls up the hill
  and
• the magnitude is .5 m/s2.
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• Do Practice Problems p. 64 6-11
• Do 3.1 Section Review p. 64 12-17