CHAPTER 2 Get ready to take notes!

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CHAPTER 2Get ready to take notes!
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Ch. 2 Motion and Speed
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• Motion when an object changes position
  relative to a reference point

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• Distance - how far an object moves
• Displacement - distance and direction relative to
  an objects starting position

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• Distance _____ m
• Displacement _____ m

0
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• Speed - distance an object travels per unit of
  time
• speed distance
• time

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• Speed that doesnt change over time is constant
  speed.
• The red and green car are traveling at a
  constant speed.

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• In real life, speed is usually not constant most
  objects have changing speed.

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• Average speed - speed of motion when speed
  changes
• Average speed is used to describe everyday motion.

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• Avg. speed total distance
• total travel time
• ____ m ____ m/hr
• hr

5
25
0.2
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• (Hint Each burst of motion happens in 1 second.
  Count the number of movements.)
• red car ____ m ___ m/s
• s
• blue car ____ m ___ m/s
• s

120
12
10
60
6
10
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• Velocity - speed and direction relative to
  starting position.

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• Determine the average speed and the average
  velocity of the skier during the 3 minutes.

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• average speed
• m m/min
• min
• average velocity
• m, m ,
• min min

420
140
3
140
right
right
46.7
3
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• Instantaneous speed - speed at any given point in
  time.

Your speedometer shows instantaneous speed.
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• Acceleration change in speed or direction or
  both.

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• Roller coasters show that changes in
  speed and/or
  direction cause acceleration.
• Positive acceleration increasing speed.
• Negative acceleration decreasing speed.

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• Acceleration
• change in velocity
• time
• Change in velocity final velocity
  initial velocity
• Unit - meters per second squared (m/s2)

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Graphing Motion
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• A distance-time graph displays motion of an
  object over time.
• Plot
• distance on
  the y-axis
  
• time
  on the
  x-axis.

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• Green Straight line, pos. slope constant
  speed to right.
• Red Straight line, lower pos. slope slower
  constant speed. A flat line no motion.
  Straight line, neg. slope constant speed, going
  left.
• Blue Curved line changing speed or
  acceleration.

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• Albert runs faster and faster (accelerates)
  steadily.
• Bob is also accelerating but at slower speeds
  than Albert.
• Charlie travels
• at a constant speed of about 6 m/s for 8 s,
• stops for 5 s,
• accelerates for 5 s more.

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• Who won the race?

Albert, because he ran the distance in the least
time.
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Slow, Constant, Left
Slow, Constant, Right
Fast, Constant, Left
Fast, Constant, Right
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• constant velocity in the positive direction
  (right)

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• constant velocity in the negative direction (left)

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• The blue car starts ahead of
  the red car (to the left of the
  screen). Since the red car is moving faster, it
  catches up with and passes the blue car.

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• Observe the velocity-time graphs. Each car's
  motion is represented by a horizontal line
  (constant velocity).

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• Observe that
  even though the
  cars pass each
  other, the lines on the velocity-time graphs do
  not intersect. Since the cars never have the
  same velocity, the lines on the velocity-time
  graph never cross.

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• The lines would intersect
  for a position vs.
  time graph the red car passing the blue car
  means that there is an instant when they occupy
  the same position (at 7 s) yet they never have
  the same velocity at any instant in time.

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• A velocity-time graph displays speed of an object
  over time.
• Plot
• velocity on
  the y-axis
  
• time
  on the
  x-axis.

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Positive Velocity, Positive Acceleration

• Positive Velocity, Zero Acceleration

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Negative Velocity, Negative Acceleration

• Negative Velocity, Zero Acceleration

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• dist.-time graph - up curve
• vel.-time graph - pos. slope
• acc.-time graph - above zero
• Positive acceleration

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• dist.-time graph - down curve
• vel.-time graph - neg. slope
• acc.-time graph - below zero
• Negative Acceleration

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Motion and Forces
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• Force - a push or pull one
  body applies to another. A force
  can cause an objects motion to change.
• When two or more forces combine at the same time,
  they create a net force.

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• Balanced forces are equal in size and opposite in
  direction.
• Unbalanced forces are unequal in size and/or not
  in the same direction.

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• Inertia and Mass

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• Inertia - an objects resistance to any change in
  motion.
• Objects with greater mass have greater inertia.

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• Newtons 1st law of
  motion - an object
  moving at a
  constant velocity
  keeps moving at
  that velocity
  unless a net force
  acts on it an object
  at rest will stay at rest unless a net force acts
  on it.

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• Auto crash - inertia at work
• Passengers not wearing a seat belt continue
  forward at that speed even after the car stops.

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• Passengers wearing a seat belt slow down as the
  car slows down.

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THE END