Unit 2: Motion-- Speed and Velocity and Acceleration

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Unit 2 Motion-- Speed and Velocity and
Acceleration
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Whats the difference between distance and
displacement?

• Distance the total magnitude traveled
• Displacement the shortest distance from the
  starting point to the ending point
• Draw label this picture on the top half of your
  left page?

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What is speed?

• SpeedThe rate of change in distance with respect
  to time.
• Even objects that are not moving have a speed 0
  m/s
• Units m/s, cm/s, mph
• Since speed is built from distance, a scalar
  quantity, then speed is also a scalar quantity. 
• Scalar Quantities carry no direction information
  with them.

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What is Velocity?

• The rate of change in displacement with respect
  to time. 
• Since displacement is a vector quantity, then
  velocity is also a vector quantity. 
• Vector Quantities have both magnitude and
  direction.
• vd/t
• v velocity (m/s)
• d distance (m)
• t time (s)
• Draw the triangle on your left page!

D
T
V
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Speed Velocity Examples

• Speed is distance divided by time
• 2 cm/s
• Velocity includes the direction
• 2 cm/s west

West
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What is the difference between average velocity
and instantaneous velocity?

• Average Velocity The longer the time period
  measured, the more it leads to calculating an
  average velocity.
• Instantaneous Velocity The shorter the time
  period measured the closer it brings you to
  calculating an "instantaneous velocity".  Only if
  the time period becomes zero would we truly have
  an instantaneous velocity. 

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Using Graphs to Calculate Speed

• We use graphical models to predict speed
• Graphical- mathematical model
• Independent on x axis what you change/test (MIX)
• Dependent on y axis what you measure
• (DRY)
• Position- where an object is, including
  direction, compared to where it was
• Distance- length w/o regard to direction
• Can get speed from slope of position versus time
  graph
• Slope Rise/run

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Acceleration

• Acceleration occurs when your speed changes up
  or down (or when you change direction).
• It is the rate speed changes
• Level ground- no acceleration due to gravity
• Steep down hill- acceleration due to gravity
• Steeper hill more acceleration

• Deceleration is slowing down
• Zero acceleration is at a constant speed

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Acceleration

• Acceleration change in speed (cm/sec)
• time (sec)
• a vf-vi
• t
• Units cm/secsec or cm/sec2

• Can use a graph to show acceleration
• slope acceleration (speed up)
• - slope - acceleration (slow down)
• 0 slope no acceleration

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• Free Fall-
• Drop straight down
• Acceleration due to gravity 9.8 m/sec2

• Terminal Velocity-
• Highest velocity reached by a falling object
• When an object stops accelerating, but continues
  to fall
• When air resistance balances the pull of gravity