Chapter 3 Physics

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Chapter 3 Physics

• Now were moving!
• Kung Fu Pong Clip

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In 1997 clocked at 766.109 mph
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FYI Sonic Boom

• It is due to the fact that a supersonic aircraft
  is traveling faster than its own sound and we
  don't hear a gradual increase in the sound level.
  Instead, the sound arrives all at once after the
  aircraft has passed overhead.
• In conclusion, when you hear a sonic boom, the
  aircraft is already traveling at a speed which is
  above the speed of sound. If you were present
  when an aircraft accelerated through the speed of
  sound, you would have already heard the aircraft
  and it is unlikely that you would hear any bang
  or boom-like sound.

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What is motion?

• What are the key words to describe motion?
• Where is motion?

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Which way did it go?

• Slowly swing the rubber stopper in a circle
  around your head and then let go of the string.
• Describe the motion of the stopper after it was
  let go.

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Motion in your body

• Spin one person on a chair for 1 min. Have this
  person stand up and walk.
• What has happened?

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Scalar vs. Vector Quantities

• Scalar has a magnitude, but no direction
• Vector has a magnitude and a direction

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Scalar or Vector?

• Which of the following would be scalar and which
  are vector quantities?
• 5 dm.
• 30 m/sec, East
• 5 mi., North
• 20 degrees Celsius
• 256 bytes
• 4000 Calories

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Conventions

• Are agreements about the way something will be
  done.
• Important for correct terminology to describe
  motion

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Distance

• Symbol?
• Calculation?
• Vector or Scalar quantity?
• Standard unit?

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Time

• Symbol?
• Calculation?
• Vector or Scalar quantity?
• Standard unit?
• Time interval describes the duration of the
  event.
• How is this different from time?

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Position

• Describes an objects location in relation to a
  particular viewpoint.
• Example Throwing a ball on a train.
• Vector or Scalar quantity?
• Standard unit?

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Displacement

• Symbol?
• Calculation?
• Vector or Scalar quantity?
• Standard unit?

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Velocity

• Symbol?
• Calculation?
• Vector or Scalar quantity?
• Standard unit?

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Speed

• Symbol?
• Vector or Scalar quantity?
• Standard unit?
• Visit the site http//www.physics.ucla.edu/demoweb
  /demomanual/mechanics/gravitational_acceleration/g
  uinea_and_feather_tube.html
• Play feather on the moon clip

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Acceleration

• Vector or Scalar quantity?
• Standard unit?

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The differences between distance and displacement

• Visit the site
• http//www.physics.gatech.edu/academics/classes/22
  11/main/demos/displacement/DDis.html
• If you were to walk the following, what would be
  the distance and the displacement?

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The difference between speed and velocity

• The only real difference is that velocity
  indicates the direction of motion.
• You use displacement, instead of distance

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Linear Motion straight line

• For diagrams you will show the direction with
  either a (right or up of the starting point) or
  a (left or down of the starting point)
• Example Which is faster?
• -20 m/s or 20 m/s

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Motion of a Pendulum

• Q What will the shape of a pendulum swinging be
  on a position-time graph?
• Q Will there be any difference if the weight on
  the pendulum is changed to a heavier object?

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Handouts

• Calculating Time Intervals and Displacements
• The Bug Race

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Calculating Speed

• Average Speed ?distance
• ? time
• Instantaneous speed
• distance travelling
• specific instant of time

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Constant Motion (uniform motion)

• If you are moving 2 m/s, how far have you moved
  in 5 seconds?
• What would be the shape of the line on a
  position-time graph for uniform motion?

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Variable Motion

• You move 2m/s then 3m/s and then stop.
• What would be the shape of the line on a
  position-time graph be for variable motion?

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Calculating Velocity

• Same as speed, except displacement is used.
• Velocity is the rate of change of position
• Acceleration is the rate of change of velocity
• Rate of change is Total Change
• ? t

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Arrows and Vectors

• The arrows indicate the size of the vector
• The larger the vector the faster it is
• Click for animation

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Measuring Motion

• Ticker Tape a method where a mark is made at
  regular time periods at the position of the
  moving object.

Equally spaced
More space between them
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Activity

• Obtain a strip of ticker tape, calculate
• Total displacement
• Displacement for each 1 second time interval
• Identify each time interval as acceleration,
  deceleration, or constant motion.
• Calculate the Average velocity
• Calculate the velocity for each 1 second time
  intervals

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Activity - Alternate

• Load up the metronome at http//www.metronomeonlin
  e.com/
• Obtain a length of tape, a car and a pen
• Push the car beside the tape and record the
  position of the car when your hear the sound from
  the metronome
• Calculate the average velocity of the car.
• Draw a position-time graph of the car

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Text Questions

• Page 313 3, 4, 5, 6,
• Page 316 6, 7, 8, 10

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Calculating the speed of cars

• Complete the following table

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Graphing Position vs Time graph

• Use the data from the cars and plot on the graph

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Graphing Uniform and Variable Motion

• What do these graphs tell us?

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• Which object(s) is(are) maintaining a state of
  motion (i.e., maintaining a constant velocity)?
• 2. Which object(s) is(are) accelerating?
• 3. Which object(s) is(are) not moving?
• 4. Which object(s) change(s) its direction?
• 5. Which object is traveling fastest?
• 6. Which moving object is traveling slowest?
• 7. Which object has the greatest acceleration?

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Making a tangent line

• A straight line is a tangent line, if it touches
  the curve at just one point.

Calculate the instantaneous velocity at 1.5 s
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Velocity-Time Graphs

• The graph shows acceleration
• Page 343

No acceleration
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Velocity-time graphs

• What is happening in the following graph?

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Investigation 11-B

• Answer 1, 5, 6, 8

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Calculating Acceleration

• Acceleration Change in velocity
• change in time
• aav vf vi
• tf ti
• /- are important, but should also include a
  direction

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Accelerationwhat we will use

• ExampleA car that is traveling 10 m/s and then
  goes to 5 m/s in 1 s.
• Answers
• Accelerating at -5 m/s2 as it slows down to the
  right

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Questions?!?

• Page 357 b-d

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Velocity-time graphs and displacement

• The area gives the displacement
• What is the displacement for