Chapter 2 Linear Motion - PowerPoint PPT Presentation

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Chapter 2 Linear Motion


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

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Title: Chapter 2 Linear Motion

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

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
  • In this class, when we talk about motion we will
    be looking at it relative to the surface of the

  • SPEED is the measure of how fast something is
    moving, or the rate at which a distance is
  • 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.

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

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

Velocity (cont.)
  • Constant velocity means constant speed and
    constant direction
  • Changing velocity can mean either speed or
    direction are changing or both!

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

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.

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

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

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.

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.

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.

Free Fall (cont.)
  • d vot ½ gt2 d is distance, g is
    acceleration due to gravity, and t is the elapsed
  • The equation can also be written as d vot 1/2

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
  • 2. A diagonal line indicates constant velocity
  • 3. A curved line or a line that stops and starts
    indicates there is some acceleration happening

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
  • A diagonal line indicates a constant acceleration
  • A line that is not straight indicates an
    acceleration that is not constant.

Air Resistance 2.8
  • Air resistance changes the motion of all moving

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