Common Sense Concepts About Motion

1
Common Sense Concepts About Motion

• By Ibrahim Abou Halloun and David Hestenes
• Presented by
• Jonathan McLaughlin and Keith Magni

2
Overview

• Common Sense Beliefs
• Categories of Alternative Conceptions
• Aristotelian
• Impetus
• Common Sense Concepts of College Students
• Taxonomy of Common Sense Concepts about Motion

3
Common Sense Beliefs

• every one of the misconceptions about motion
  common among students today was seriously
  advocated by leading intellectuals in
  pre-Newtonian times.

4
Common Sense Beliefs

• common sense beliefs should be treated with
  genuine respect by instructors. They should be
  regarded as serous alternative hypotheses to be
  evaluated by scientific procedures.

5
Aristotelian Physics

• The speed of an object is proportional to its
  weight.
• vW/R
• Quantitative physics was impossible.
• Only living things can apply a force. Non-living
  things can only stop or guide motion.

6
Aristotelian Physics

• Forces only move an object when they overcome an
  objects resistance (related to inertia/weight).
• VF/R
• Without a force, an object comes to rest
  immediately.
• Free-falling objects increase their weight as
  they get closer to their natural place on earth.
• Mediums can both resist motion and propel an
  object.

7
Impetus Physics

• the active agent imparts to the
• object a certain immaterial motive power
  which sustains the bodys motion until it has
  been
• dissipated due to resistance.

8
Impetus Physics

• Allows for the explanation of
• circular impetus persistent
• motion of the planets and
• the grinders wheel.
• Allows for motion in a vacuum

9
Impetus Physics

• The Historical Precursor of momentum and Kinetic
  Energy.

10
Impetus Physics

• Albert of Saxony uses Impetus
• to explain projectile motion.

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Impetus Physics

• A of S on Projectile Motion
• Compromise between
• Impetus
• Gravity
• Air resistance

12
Impetus Physics

• A of S on Projectile Motion
• Three Stage Trajectory
• Initial Stage impetus suppresses the effect of
  gravity.
• Intermediate Stage shows compromise between
  impetus and gravity.
• Final Stage the projectile falls vertically in
  natural Motion.

13
Impetus Physics

• Kinematical Ideas also developed in the14th
  century along w/ Impetus theory.
• Distinctions made between uniform velocity
  uniform acceleration, and non-uniform
  acceleration.
• Resulting in birth of concepts of instantaneous
  velocity and acceleration.

14
Impetus Physics

• Kinematical Ideas developed in 14th Century
• Oresme develops graphical method of representing
  variable quantities.
• Used to derive Mertonian Mean Speed Rule.

15
Impetus Physics

• Kinematical Ideas developed in the 14th century
• in a given time interval, the distance
  traveled w/ uniform acceleration is equal to the
  distance traveled w/ uniform speed equal to the
  instantaneous speed in the accelerated motion at
  the middle instant of the time interval.

16
Impetus Physics

• Kinematical Ideas developed in the 14th century
• These developments were essential prerequisites
  for Galileos kinematical analysis of projectile
  
• motion.

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Common Sense Concepts of College Students

• 478 Students given a multiple choice diagnostic
  pre/post-test used to assess common sense
  concepts.
• Alternative answers on test correspond with
  Aristotelian and Impetus theories.
• 22 students were further interviewed to gain
  further insight into conceptions.

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Pre/Post-Test Results

• 18 of students answers were predominantly
  Aristotelian.
• 65 of students answers were predominantly
  Impetus type.
• 17 of students answers were predominantly
  Newtonian.

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Pre/Post-Test Highlights

• Students demonstrated a belief that
• an object slows down if no net force is applied
  (47/20).
• an object under constant force moves at constant
  speed (66 /54).
• an impetus is required to keep an object moving
  (65/44).

20
Student Interviews

• Students were asked questions about their
  conceptions of
• General concepts of motion
• Free particle motion
• One-dimensional motion under a constant force
• Two-dimensional motion under a constant force

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General Concepts of Motion

• Students had difficulty distinguishing between
  kinematical concepts.
• Students believed that inanimate objects may stop
  or redirect objects but cannot generate force.

22
General Concepts of Motion

• Students believed that gravity is an impetus
  force.
• Students accepted the existence of a vacuum, but
  insisted that motion could not occur outside of a
  material medium.

23
Free-Particle Motion

• Students with Aristotelian beliefs had bizarre
  arguments.
• Ex) A block sliding on a surface would come to
  rest because you need wheels to keep it going.
• Students with impetus beliefs varied in their
  explanations. Some believed that objects begin
  losing impetus immediately, while other believed
  that objects lose impetus when they encounter
  resistance.

24
One-Dimensional Motion Under A Constant Force

• Some students believed that objects under
  constant force would speed up but eventually a
  speed limit would be reached.

25
Two-Dimensional Motion Under A Constant Force

• Students had a concept of projectile motion and
  that the path of a projectile was parabolic, but
  had trouble identifying that projectile motion
  was the result of a constant force.

26
Consistency of Ideas

• Students were inconsistent in their responses,
  however, students with quasi-Newtonian beliefs
  were much more consistent in their beliefs.
• Students who showed common-sense ideas used a mix
  of Aristotelian and Impetus type explanations for
  physical events.

27
Consistency of Ideas

• much of the incoherence in the student CS
  common sense systems is the result of vague and
  undifferentiated concepts.

28
Persistence of Alternative Concepts

• As a rule, students held firm to mistaken
  beliefs even when confronted with phenomena that
  contradicted those beliefs.
• Students tended not to contradict their own
  beliefs but to attribute the contradiction to
  some other principle.

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Persistence of Alternative Concepts

• We doubt that a demonstration can be effective
  unless it is performed in a context that elicits
  and helps to resolve conflicts between common
  sense and specific scientific concepts.

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Persistence of Alternative Concepts

• students who showed obstinate beliefs were able
  to come to adequate justifications, mostly not
  because they have seen something in conflict
  with their beliefs, but because they came to
  realize the inconsistency of their thinking when
  asked to reflect on their own arguments.

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Taxonomy of Common Sense Concepts About Motion

• Principles of Motion
• Correspond to Newtons Laws
• Influences on Motion
• Correspond to Force influences