PHYSICS LAB DIVISION C

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PHYSICS LAB DIVISION C

• CIRCULAR MOTION 2007

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Event Particulars

• Two student team
• Topic Rotational Motion
• Students can only bring a non-programmable
  calculator
• Students are expected to know the basic concepts,
  definitions and mathematical statements.

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Event Particulars

• Questions will relate to rotational motion about
  a fixed axis including rolling objects.
• Students are expected to know the basic equations
  of motion involving constant angular
  acceleration, moment of inertia, torque,
  rotational energy including friction and power.
• All answers need to be provided in SI units and
  correct significant figures.

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Sample Stations

• The measurement and/or calculation of centripetal
  force.
• The measurement and/or calculation of moment of
  inertia
• The measurement and/or calculation of angular
  momentum or conservation of angular moment

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Sample station

• Determine the mechanical advantage and efficiency
  of a gear train and/or pulley and belt system
• The measurement and /or calculation of torque

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Students will probably see

• A demonstration of data collection by computer or
  calculator probes then given a prepared data set
  to analyze and interpret the data.
• A test with problems from all areas of rotational
  motion.

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SCORING

• Points will be awarded for correct answers,
  measurements, calculations and analysis of data.
• Ties will be broken using a designated tasks or
  questions that may be noted on the student answer
  form.

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Example of Lab

• This is a typical centripetal force lab
  probability completed by all introductory Physics
  students

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Circular MotionObjectives Determine
relationship between linear velocity, centripetal
force and acceleration.Equipment stopwatch, Fc
setup, mass set
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Methods

• 1. Sketch the Fc setup. Label the radius, Fc,
  mass m, reference washer, mass holder.
• 2. Measure the radius with the reference
  washer at its desired position. Hang a 50.0 g
  mass on the Fc set up. This mass represents a
  force Fc mv2/r. Let g 10m/s2 such that a
  50.0 g mass has a weight Fc equal to 0.5 N.
• 3. Put your goggles on now. Whirl and time
  the stopper for 10 revs in a horizontal circle.
  Be sure the reference washer does not move up and
  down, and does not touch the handle.

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• Determine the period T (time) for one revolution,
  then calculate v, and ac. The radius remains
  constant in this lab.           v 2pr/T
  and ac v2/r.
• Repeat for various masses to get 4-5 trials (up
  to a maximum of 250 g).

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Analysis

• 1. Plot graphs of             (a) Fc vs ac
  (ac on the x-axis)             (b) v2 vs ac
  (ac on the x-axis)
• 2. Describe the relationship for each graph.
  Calculate the slopes for each. What do the
  slopes of each graph represent? (Hint look at
  the units for ?y/?x, then examine your data.)

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• 3. Describe how adjustments in the radius r would
  affect the velocity given the same Fc.

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Sample Data Table

• radius 0.85 m C 2 p r,
  T time/revs, v 2pr
  / T Let g 10 m/s2
•   mass kg0.050,   Fc (N) 0.50,
  revs 10   time (s) 7.2  
• T(s) 72s   v  (m/s) 7.4  
• v2 (m2/s2) 55 ac (m/s2)   65            

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Simulation Labs (Physlets)

• Go to rolling question
• Go to turntable question
• Walker physlets questions
• Second law of rotation lab
• Mass on turntable

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Examples of general circular motion questions
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Basic Rotational Quantities
In addition to any tangential acceleration, there
is always the centripetal acceleration
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Basic Rotational Quantities

• The angular displancment is defined by

For a circular path it follows that the angular
velocity is
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Angular Velocity
For an object rotating about an axis, every point
on the object on the object has the same angular
velocity. The tangential velocity of any point is
proportional to its distance from the axis of
rotation. Angular velocity has the units rad/s.
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Angular Velocity

• Angular velocity is the rate of change of angular
  displacement and can be described by the
  relationship
• and if v is constant, the angle can be calculated
  from