Chapter 2 and 3 Motion and Accelerated Motion

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Chapter 2 and 3Motion and Accelerated Motion

• Types of Quantities in Physics
• 1. Scalar- Magnitude(size)
• examples speed, volume, temp. mass
• 2. Vector- magnitude and direction
• examples velocity, acceleration, force
• Resultant- vector representing sum of 2 vectors

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Time intervals and Displacement

• Time Interval- difference between 2 times
• ? ? change in a quantity
• ?t tf-ti
• Displacement- change in position
• ?d

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Position-Time Graphs

• Can be used to find the velocity and position of
  an object

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Velocity

• Speed in a given direction
• What type of quantity is velocity?
• Vector
• Average Velocity(v) ?d/ ?t or
• df-di/tf-ti
• Instantaneous Velocity- speed and direction at
  a particular instant
• example speedometer

?
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Determining position with average velocity

• dvt di or
• dvt if di 0

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Ch. 3Accelerated Motion

• What is acceleration?
• - rate of change of velocity
• a vf - vi / t or a ?v / ?t
• measured in m/s2
• http//www.glenbrook.k12.il.us/gbssci/phys/mmedia/
  kinema/acceln.html

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Types of Acceleration

• Constant acceleration- velocity changes at a
  constant rate
• Instantaneous acceleration- change in velocity at
  an instant of time
• Deceleration- negative acceleration

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Motion with Constant Acceleration

• Final velocity with average acceleration
• a ?v / ?t
• a ?t vf vi
• vf vi a ?t

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Examples(p.65)

• 18a. A golf ball rolls up a hill toward a
  miniature-golf hole. Assume that the direction
  toward the hole is positive. If the golf ball
  starts with a speed of 2.0 m/s and slows at a
  constant rate of .50 m/s/s, what is its velocity
  after 2.0 s?

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Example(p.65)

• 20. If a car accelerates from rest at a constant
  5.5 m/s/s, how long will it take for the car to
  reach a velocity of 28 m/s?

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B. Position with average acceleration

• d vit ½ at2
• Example A car starting from rest is accelerated
  at 6.1 m/s/s. What is the cars displacement
  during the first 7.0 s of acceleration?

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What is the difference between displacement and
distance?

• Distance is a scalar quantity which refers to
  "how much ground an object has covered" during
  its motion.
• Displacement is a vector quantity which refers to
  "how far out of place an object is" it is the
  object's overall change in position.
• To test your understanding of this distinction,
  consider the motion depicted in the diagram
  below. A physics teacher walks 4 meters East, 2
  meters South, 4 meters West, and finally 2 meters
  North.

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C. Velocity with Constant Acceleration

• vf2 vi2 2ad
• Example A plane is accelerated from a speed of
  2.0 m/s at the constant rate of 3.0 m/s/s over a
  distance of 530 m. What is its speed after
  traveling this distance?

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D. Displacement(Position) during Uniform
Acceleration

• d ½ ( vf vi) t
• Example A race car traveling south at 44 m/s is
  uniformly decelerated to a velocity of 22 m/s
  over an 11 second interval. What is its
  displacement during this time?

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What is Kinematics?

• The mathematical description of motion
• The science of describing the motion of objects
  using words, diagrams, numbers, graphs, and
  equations.

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Example(p. 71)

• A man runs at a velocity of 4.5 m/s for 15.0 min.
  When going up an increasingly steep hill, he
  slows down a constant rate of 0.05 m/s/s for 90.0
  s and comes to a stop. How far did he run?
• Hint This requires two steps.

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Example( p. 71)

• 32. You start your bicycle at the tip of a hill.
  You coast down the hill at a constant
  acceleration of 2.00 m/s/s. When you get to the
  bottom of the hill, you are moving at 18.0 m/s,
  ad you pedal to maintain that speed. If you
  continue at this speed for 1.00 min., how far
  will you have gone from the time you left the
  hilltop?

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Free Fall

• Free Fall
• The motion of a body when air resistance is
  negligible and the motion can be considered due
  to the force of gravity

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Acceleration due to Gravity

• Acceleration of an object in free fall that
  results from Earths gravity
• Has the symbol g
• g 9.8 m/s/s ( average value)
• It is a positive number
• If your coordinate system defines upward to be
  the positive direction, then acceleration due to
  gravity is g and vice versa.
• So in other words a -g or ag.

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Examples p.74

• 42. A construction worker accidentally drops a
  brick from a high scaffold.
• What is the velocity of the brick after 4.0 s?
• How far does the brick fall during this time?

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More examples

• 45. A tennis ball is thrown straight up with an
  initial speed of 22.5 m/s. It is caught at the
  same distance above the ground.
• a. How high does the ball rise?
• b. How long does the ball remain in the air?