Chapter 2 Linear Motion

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Chapter 2Linear Motion
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• Motion of some form is responsible for nearly
  everything we see, do, or experience in our daily
  lives.
• Quantity divided by time is RATE

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Motion is Relative - 2.1

• When we see things move in the world around us,
  they are moving relative to us and our position.
• It is important to realize that in relative to
  the sun and stars everything on the earth is
  moving.
• In this class, when we talk about motion we will
  be looking at it relative to the surface of the
  earth.

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SPEED 2.2

• SPEED is the measure of how fast something is
  moving, or the rate at which a distance is
  covered.
• Speed distance / time
• The units for speed can be any measure of
  distance over any measure of time. It is written
  as Dist./Time
• The speed of any object at any given instant is
  its instantaneous speed.

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Speed (cont.)

• The speed of any object over a period of time is
  its average speed.
• When distinguishing between instantaneous and
  average speed think of a road trip.
• The equation for average speed is total distance
  divided by total time interval.
• Speed Dist. / Time

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Velocity 2.3

• There is a difference between speed and
  velocity Speed is how fast you are
  traveling Velocity is how fast you are traveling
  and what direction you are going. This means
  that your speed can be constant while your
  velocity is changing if you are going around a
  turn.

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Velocity (cont.)

• Constant velocity means constant speed and
  constant direction
• Changing velocity can mean either speed or
  direction are changing or both!

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Acceleration 2.4

• When velocity is changing then we have
  acceleration. Acceleration change in
  velocity / time interval
• Acceleration applies to both a increases and
  decreases in speed (often times we use the term
  deceleration when we talk about slowing down, but
  in physics we use acceleration for both)
• Acceleration also applies to change in direction.
• The units used is distance / time / time
• or distance / time2

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Free Fall 2.5 How Fast

• When an object is dropped it falls, and as it
  falls its speed increases. If we neglect air
  resistance, we say it is free falling if no other
  forces are acting on it except gravity. The
  amount of time that has passed since the
  beginning of the fall is the elapsed time.

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Free Fall (cont.)

• To get the instantaneous speed of an object in
  free fall that is dropped from rest we say
  velocity equals acceleration times time, where
  acceleration is due to gravity.
• v gt V is velocity, g is acceleration
  due to gravity, and t is elapsed time
• This equation can be written as v at a is
  acceleration an object undergoes

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Free Fall (cont.)

• The acceleration due to gravity is equal to 9.8
  m/s/s, which we commonly round to 10
  m/s/s. This means for each second an object
  falls, its instantaneous speed increases 10
  m/s.

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Free Fall (cont.)

• All rules for an object in free fall that is
  falling downward also apply to an object in free
  fall upwards, except in this case, the
  acceleration due to gravity is negative and the
  speed is decreases each second by 10 m/s.

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Free Fall 2.6 How Far

• When looking at how far an object falls in free
  fall it is important to remember the difference
  between instantaneous and average speed. Remember
  that average speed is how far an object has
  traveled divided by the amount of time it has
  been traveling. This means that after one
  second an object in free fall is falling 10 m/s.
  It started at 0 m/s. The average of 10 and 0 is
  5, so the average speed for one second is 5 m/s.

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Free Fall (cont.)

• Put this into the equation Average Velocity
  distance traveled / time period
• we get a distance of 5 m
• This could get complicated if we start looking at
  longer time periods, because each second the
  speed is changing. To deal with this we use the
  following equation.

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Free Fall (cont.)

• d vot ½ gt2 d is distance, g is
  acceleration due to gravity, and t is the elapsed
  time
• The equation can also be written as d vot 1/2
  at2

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Graphs of Motion 2.7

• Some times it is easier to look at a graph to see
  the relationships between distance, velocity, and
  acceleration. Here are some guidelines for
  looking at motion graphs
• Distance VS Time graphs
• 1. a flat straight line indicates there is no
  acceleration.
• 2. A diagonal line indicates constant velocity
• 3. A curved line or a line that stops and starts
  indicates there is some acceleration happening

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Graphs of Motion

• Velocity VS Time graphs
• A flat line indicates there is motion, but it is
  happening at a constant rate and there is no
  acceleration.
• A diagonal line indicates a constant acceleration
• A line that is not straight indicates an
  acceleration that is not constant.

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Air Resistance 2.8

• Air resistance changes the motion of all moving
  objects.

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