Uniform and Instantaneous Velocity

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Uniform and Instantaneous Velocity
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Opening Ideas

• What is the closest thing to uniform motion that
  you have ever observed?
• What factors might prevent objects from moving
  uniformly on Earth or in space?
• What other phenomena besides uniform motion
  cannot be observed directly, even in the best
  lab, and must be inferred from imperfect
  observations?

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Uniform Motion

• Predicting the behaviour of moving objects can be
  very complex..
• uniform motion motion at constant velocity,
  with no change in speed or direction.

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How can you tell if an object is moving uniformly?

• You need to check whether it has constant
  velocity neither its speed nor its direction is
  changing.
• Direction must be moving in a straight line,
  forward or back, up or down.
• Speed can be measured in many ways, including
  speedometers, radar guns etc.

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Remember Graph shapes of uniform motion
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Position-time graph of tightrope walker
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Average or Instantaneous?

• Instantaneous velocity the velocity of a
  moving object at one specific moment.
• Average velocity velocity measured over a
  certain time interval.
• In many situations like getting a speeding
  ticket, average velocity is less important than
  instantaneous velocity. Explain why in your own
  words.

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Calculating average velocity from a position-time
graph

• Each section of the graph has a different slope
  representing individual velocities at that stage
  of the journey.
• Calculate them by finding individual slopes of
  that section of the graph.
• The average velocity of the total graph or trip
  is found by using the beginning and end points.

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Pause reflect

• Sketch a position-time graph of each object
  listed below. Describe its slope as positive or
  negative, and as constant, increasing, or
  decreasing.
• A) a stone at rest
• B) a jogger moving steadily to the right
• C) a bicycle moving to the left and slowing down
• D) a rocket moving up at an increasing speed
• E) a stone falling freely with increasing speed
• F) a parachutist drifting down at a steady speed

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Homework

• Pg 329 1-4