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					Concept Summary
Batesville High School Physics
         Motion of What?
 To  simplify things as much as possible,
 we will first consider one-dimensional
 motion (motion along a straight line) of
 particles (points that can’t spin, rotate,
 flip, flop, or wiggle around).
        Describing Motions
 We  will concern ourselves (for now) with
  describing motion - kinematics.
 We will worry about explaining motion
  (dynamics) later.
       Two Simple Motions
 Inour course, we will be primarily
  concerned describing with 2 simple
  motions:
   Motion with constant velocity
   Motion with constant acceleration
                Position
 Mark  a zero point on the line, pick a
  direction to be positive, and measure
  from there.
 Positions can be positive or negative.
 Units of position: centimeters, meters,
  kilometers, inches, feet, miles, etc.
 Common symbol: x
      Operational Definition
 Position,like other physical quantities,
 is defined by telling how you go about
 measuring it - not by giving synonyms
 or descriptive phrases. This is called an
 operational definition.
Positions are Relative
 Different people can mark the line
  differently, so they can get different
  numbers for position.
 The position number (and unit) really
  don’t mean anything until you specify
  where you marked “0”, and which way
  you made positive - your frame of
  reference.
           Displacement
 Displacement   = net distance moved or
  net change in position
 Common symbol, d or ∆x
 If you move from xo to x,
  displacement, d = ∆x = x - xo
                 Rates
A  rate measures how fast something
  changes.
 In physics, a rate is almost always
  calculated as a quantity divided by time.
 Rate Q changes =        change in Q
                        time for Q to change
                 Speed
 Speed   is the rate position changes, or
  the rate distance is covered.
 There are two kinds of speed:
   Average  speed
   Instantaneous speed
             Average Speed
   Average speed = distance traveled
                        time it takes
   Or, average speed = displacement
                               time
   In symbols, v = d or ∆x
                    t     t

   Units of speed: m/s, km/h, mi/h, etc.
      Instantaneous Speed
 Instantaneous  speed is what the
  speedometer says.
 It is not measured over a time interval,
  like average speed.
         Constant Speed
 Ifan object’s instantaneous speed is
  always the same value, the object has a
  constant speed.
 In this case, average speed =
  instantaneous speed
                 Velocity
 Velocity = speed + direction
 2 kinds of velocity
   Average   velocity = average speed +
    direction
   Instantaneous velocity = instantaneous
    speed + direction
         How Velocity Changes
 The    velocity of an object changes if:
   It speeds up, or
   It slows down, or

   It changes direction.
       What Velocity Means
 Anobject’s velocity tells you how fast its
 position is changing.
  5  m/s means the object’s position changes
    by 5 meters each second.
   60 mi/hr means that the object’s position
    changes by 60 mi each hour.
     Velocities are Relative
 Speed   and velocity are relative
  quantities. Different observers, in
  different frames of reference, can
  measure different velocities.
 You measure speed and velocity by
  comparing two motions.
              Acceleration
 Accelerationis the rate velocity (not
  speed) changes.
 2 kinds:
   Average  acceleration
   Instantaneous acceleration
         Average Acceleration
   Ave. Accel. = change in velocity
                    time it takes
    in symbols, a = ∆v
                    t



Accelerations are not relative quantities.
       Units of Acceleration
 Since  acceleration is a velocity divided
  by a time, its units are a distance unit
  divided by 2 time units.
 This is commonly written 2 ways:
   m/s/s = m/s2
   km/hr/s = km/hr.s
       Constant Acceleration
 In many common situations, an object’s
  acceleration is constant, or at least
  approximately constant.
 In this case:
   Average   accel. = instantaneous accel.
               Free Fall
 Free fall is motion under the influence of
 gravity only - no friction or air
 resistance.
    Acceleration in Free Fall
 The  acceleration of an object in free fall
  is constant.
 At the surface of Earth, the free-fall
  acceleration is about 10 m/s2, or 9.8
  m/s2 if you have a calculator (or 32 ft/s2
  or 22 mi/hr/s in “English” units).
          Air Resistance
 Theeffect of air resistance is to slow an
 object down and/or decrease its
 acceleration.
    The End


				
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