Describing and Comparing Motions

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Describing and Comparing Motions

• SCI 201

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Driving Questions

• How can motion be described?
• How many different kinds of motions are there and
  what distinguishes them from one another?

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Some basic terms

• Position - the location of an object at any given
  time
• Motion - the act of changing position
• Distance - the amount of change of position
• Reference point - an arbitrary point on an object
  used to establish its position
• Calculating distance (d x2 - x1), where the
  symbol x represents position

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Graphing Motion

• Position can be graphed as a function of time
  Position (x) on the vertical axis and time (t) on
  the horizontal axis
• Motion sensor demo

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Conclusions from the demo

• Speed - the rate of change of position
• The slope of the x vs. t graph represents speed
  (how fast the object is moving). The steeper the
  slope, the faster the object is moving (i.e. the
  faster the slope the higher the speed)

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Calculating speed

• v d / ?t where v is the speed, d is the
  distance, and ?t is the time change
• Distance can be calculated if speed and time are
  known using d v X ?t

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When direction changes

• Displacement -the difference between an objects
  initial and final positions
• How far you traveled vs. how far you are from
  where you started a trip to the grocery store
  distance vs. displacement
• Velocity - rate of change of displacement (speed
  and direction)
• Back to the motion sensor

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Comparing motions

• Two tracks/walking activity

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Key points

• Constant velocity - equal amounts of distance
  traveled in equal amounts of time
• Accelerated motion (acceleration) - differing
  amounts of distance traveled in equal amounts of
  time
• Speeding up?
• Slowing down?
• Acceleration - rate of change of velocity
• a ? v / ? t, where a is the acceleration, ? v
  is the change in velocity, ? t is the change in
  time

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Final thoughts

• Constant velocity zero acceleration (i.e.
  motion is not changing)
• Uniform (constant) acceleration constantly
  changing velocity (i.e. motion is changing the
  same way all the time)
• Three forms of acceleration
• Speeding up, slowing down, changing direction
• How many accelerators are there on a car?

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Driving Questions

• How can motion be described?
• How many different kinds of motions are there and
  what distinguishes them from one another?