Intro to Motion

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Intro to Motion

• Uniform and Non-Uniform Motion
• Speed and Velocity

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Framing Questions

• What is the difference between uniform motion and
  non-uniform motion?
• What are examples of each?
• What is the difference between speed and
  velocity?
• What are the formulas for speed and velocity?

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Uniform vs. Non-Uniform Motion

• Uniform or constant motion is movement in a
  straight line at a constant speed
• Ex A cyclist traveling on a straight path at a
  speed of 10m/s.
• Uniform motion rarely exists how many times do
  you see something going at precisely the same
  speed in a precisely straight line?
• This is what we will explore this week constant
  velocity
• Any movement not in a straight line or not at a
  constant speed is called non-uniform motion
• Ex A car traveling around a corner
• Most enduring motions are non-uniform
• This is what we will explore next week changing
  velocity, or acceleration.

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Exercise Uniform or Non-Uniform?

• A steel ball is dropped from your raised hand to
  the floor
• A car is traveling north at a constant speed for
  2 hours
• A jogger is running around a circular track at a
  constant speed
• A car is traveling a steady 60km/h due west
• A leaf flutters to the ground
• A rocket is launched from the Earth towards the
  moon
• A motorcycle rider applies the brakes in order to
  come to a stop
• A ball at the end of a rope is whirled around a
  persons head at a constant speed of 8.0m/s
• The worlds fastest women compete in the 100m
  dash at the Olympics
• A marble rolls in a straight path down the
  hallway
• Is there ever a time when a motion which is
  non-uniform overall, is uniform at some point?

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Speed, in
Plain English

• Speed describes how fast something is moving
• It is scalar, so we indicate
• Magnitude
• Not direction
• The standard unit for measuring speed is m/s

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Speed, in
Physics Speak!

• Symbol
• Speed v
• Formula
• Speed distance
• time
• v d
• t
• Example The cyclist reached a maximum speed of
  12.0 m/s during the race.

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Velocity, in
Plain English

• Velocity describes the speed and direction of
  motion
• This means it describes how fast an objects
  position is changing
• Velocity is a vector, so we describe
• Magnitude
• Direction
• The standard unit for measuring velocity is m/s

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Velocity, in
Physics Speak!

• Symbols
• Velocity v
• Formula
• Velocity displacement
• time
• v d
• t
• Example
• The aircraft was traveling at 535km/h, headed 45
  north of west

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Practice Problem

• An object traveling at a constant speed travels
  due west for 800m in 40s.
• What is the speed of the object?
• What is the velocity of the object?
• v d/t v d/t
• 800m/40s 800m due west/40s
• 20 m/s 20 m/s due west
• Note When the object goes in a straight line,
  the magnitude for speed and velocity will always
  be the same!

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More Practice Problems

• An object traveling at a constant speed travels
  450 m in 15 s. What is the speed of the object?
• 30 m/s
• A shell from a rifle has an average speed of 960
  m/s. How many meters does it travel in 5 s? How
  many km in 5 s?
• 4800 m
• 4.8 km

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More Practice Problems

• A driver travels 25m/s on a level highway between
  two towns. It takes the driver 2h to travel
  between the two towns. How far apart are the
  towns (in kms)?
• 180 km