Velocity%20and%20speed

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Velocity and speed
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Objectives

• Compare and Contrast speed and velocity
• Use correct SI units to express speed and
  velocity
• Describe and analyze motion in one dimension
  using equations for speed, instantaneous
  velocity, and average velocity.
• Generate and interpret graphs and charts
  describing motion using speed and velocity

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Motion

• An object is in motion when there is a change in
  position when compared to another object
• Its a rate of change in position over a period
  of time
• Pause video for a moment and think about this
  question..Do all objects move at the same rate?
  How do we represent this?

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Speed

• A scalar quantity of the rate of change in
  position.
• Magnitude with units but no direction
• Units for distance are m, cm, km (etc)
• Units for time are s, min, hr
• Most common units for speed are m/s and km/hr

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Average vs. Instantaneous speed

• Average speed is the distance traveled divided by
  the time to travel.
• Instantaneous speed is the average speed for
  infinitely small distances and times.

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5. Graphing speed Configuration

• Slow walker Walk slow and steady.
• Fast walker Walk briskly but steady.
• Fast starter (Starts fast and than slows down)
  Run in a full sprint at the beginning. Be fast
  around 15m and then slow it down during the last
  15m (second half of the trip).
• Fast finisher (Starts slow and than speeds up)
  Begin with a walk, jog somewhere around 15 m and
  run in a full sprint by 25m.

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Speed Graph
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• Velocity is not the same as speed
• Speed has no direction (scalar)
• Velocity has both speed and direction (vector)

Pause for a moment and think about the
differences between the two and how their graphs
may look different.
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Velocity

• Average velocity is displacement divided by the
  time interval
• Vave ?x xf - xi
• ?t tf - ti

Remember Displacement and Velocity can be
positive or negative Time can NEVER be negative
change in position
units of (m/s, km/hr)
change in time
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Example

• During a race on level ground, Andra runs with an
  average velocity of 6.02 m/s to the east. What
  distance does Andra cover in 137 s?

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Example

• If a ball travels 36 m at a velocity of 4.2 m/s,
  how long does it take?

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Example

• If a car travels 25.0 km east in 15 minutes, what
  is the average velocity of the car?

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• Velocity can be interpreted graphically.

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• Velocity can be postive, negative, or zero (at
  rest)

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• Instantaneous velocity may not be the same as
  average velocity
• Instantaneous velocity is the velocity of some
  instant ( or specific point on its path)

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