How to Torture a Wheel

1
How to Torture a Wheel

• A Redesign of the Exploratoriums Wheel Dynamics
  Exhibit

ED333BWinter 2001 Assignment 2 Prof. Shelly
Goldman March 10, 2001 James
Sulzen jsulzen_at_stanford.edu
2
Introduction

• I am just finishing a study with Dan Schwartz of,
  among other things, how people learn about the
  dynamics of bicycle wheels. I learned much about
  wheel dynamics during the course of the study,
  and I welcome the opportunity to apply this
  knowledge to extending a related exhibit at the
  Exploratorium in San Francisco.
• The Exploratoriums Wheel Dynamics exhibit has a
  number of hands-on activities allowing visitors
  to explore the effects of spinning wheels and
  gyroscopes (see Photo 1). It has the following
  exhibit elements
• Two free-standing wheels that visitors can
  manipulate.
• A chair to sit in and use a wheel to spin oneself
  around via precessional effects (see Photo 2).
• A two-sided gyroscope mounted on a swivel base
  (see Photo 3).
• A hook and chain assembly to support a bicycle
  wheel for creating gyroscopic effects (see Photo
  4).
• Signs describing these activities and some of the
  science behind them.
• Based upon my observations, I perceive several
  problems with the exhibit
• Visitors hardly ever learn much of anything from
  their experience with the exhibit.
• The exhibit is not terribly engaging - visitors
  have a difficult time discerning what the
  meaningful activities are without reading the
  various signage. As a result almost no visitors
  stay more than a minute or so before moving on.
• Even if a visitor makes the effort to stay and to
  engage, they still are unable to learn anything
  with the present exhibit. Instead, they get to
  witness various phenomena, but are forced to walk
  away with no increased understanding of deeper
  affects or cause of the phenomena.
• The exhibit does support collaborative
  exploration very well.
• The net result is that the exhibit seems to
  produce at best a gee whiz experience.

3
Why this Problem is Important

• Wheels in general, and bicycle wheels in
  particular, are quite common ordinary everyday
  experiences. The Physics of wheel dynamics is
  taught in most all High School and college
  freshman Physics courses. Yet despite the
  ordinariness of it, and even after twice
  explicitly studying the subject in a scholastic
  career, virtually no student (nor even
  instructors as it happens) has much if any
  intuitive understanding of how all the forces
  operate in wheel dynamics. You can show the
  phenomenon from Photo 4 (the precessing wheel) to
  almost anybody and no one is able to offer a
  satisfactory let alone intuitive explanation of
  why the wheel does not pivot down when it is
  spinning.
• To quote a seventeen-year veteran of High School
  Physics teaching, I have to tell you that my
  understanding of the Physics is not supported by
  my intuitive sense Even after Ive used Physics
  to explain why the wheel stays up when suspended
  from one side by a rope I still want to ask why
  doesnt it fall down? Its magic.
• All wheel dynamics courses are structured around
  the Principle of Conservation of Angular
  Momentum. There are a number of fairly difficult
  to comprehend equations and concepts that are
  required to master this approach these provide
  no basis for an intuitive understanding of just
  what it is that happens with spinning wheels when
  you try to manipulate them. The Exploratotium
  exhibits explanation (see Photo 5) is no better
  (and in fact, I think is perhaps misleading). As
  one woman visitor said to me, after having read
  it, Whyd they even bother putting it there? It
  doesnt tell me anything. This seems to be
  pretty much the same case with how Physics
  teaches the subject to students They memorize
  the formulas for the test but inevitably lose the
  learning because no physical intuition is
  provided about gyroscopic phenomena.
• As such, there seems to be a distinct need for
  illustrating ways to develop physical intuitions
  about wheel dynamics.

4
Observations

• On March 9, I spent the last hour of the day at
  the Exploratoriums wheel exhibit and made the
  following observations (recorded over a 45 minute
  period). (See Photo 1.)
• Twenty-seven people in some thirteen groups
  stopped by and either looked at or interacted
  with the exhibit in some way. About half the
  groups had two people interact and all the others
  only had one person. Someone from four of these
  groups was observed reading signs (see Photo 6).
  None of the readers or participants seemed
  particularly enlightened (no expressions of
  comprehension or amused delight, etc.), nor were
  they able to articulately respond about what they
  had learned when I queried some of them directly
  as they were leaving the exhibit area.
• With one exception, the main form of interaction
  with the exhibit was to pick up one of the two
  free-standing bicycle wheels and spin it. Seven
  of the individuals sat in the chair and tried to
  turn themselves with the wheel (four of whom had
  difficulties and three of whom were fairly
  successful - see Photo 2). The only non-wheel
  spinning participant was a gentleman
  approximately in his sixties who saw me set up
  and use the hanging bicycle wheel to to try out
  the precession part of the exhibit (Photo 4) he
  brought back his wife several minutes later to
  show her.
• Not a single person so much as examined the
  gyroscope.
• In contrast, in the same time period, 34 people
  jumped on an adjacent exhibit that allowed a
  single participant to spin in place (see Photo
  7). Four people were observed to read its sign.
  This activity level markedly contrasts with the
  relatively lukewarm bicycle wheel participation
  by the 13 people mentioned above.

5
What Makes this Difficult to Learn

• One of the purposes of the study I did with Dan
  was to try to identify what made it so difficult
  to learn about how a bicycle wheel worked. My
  tentative conclusions are as follows
• Visual/Kinesthetic Confounding First and
  foremost, the visual and kinesthetic systems
  confound each other when playing with the wheel.
  The intuitive visual sense is that spinning
  objects should behave more or less similarly to
  non-spinning ones. However, the kinesthetic
  experience with the wheel is communicating
  something quite different from what the visual
  system seems to expect. People seem to have a
  strong bias for preferring visual inputs in these
  situations with the net result that most people
  become rather confused and deadlocked in
  developing learning around the wheel.
• Transitoriness The physical effects are very
  dynamic and transitory in nature. This makes it
  very hard to make meaningful observations as
  effects whip right past observers before they can
  quite perceive what is happening, let alone what
  caused it to happen.
• Measurement It is particularly difficult, when
  manual manipulation is the only available
  investigatory technique, to meaningfully
  calibrate or measure physical effects. Even
  ameliorating the visual and kinesthetic
  confounding still leaves it very difficult to
  feel at a sensory level, let alone a perceptual
  one, just what effect produces exactly which
  result and to what degree.
• Mechanism The mechanism of force transfer from
  the spinning hub to the axle is actually rather
  hidden, subtle, and very non-intuitive for most
  people.
• Multiple Simultaneous Manipulations and Effects
  In manipulating the wheel, people often tend to
  do several things at once without realizing it
  (such as change the spin direction, spin speed,
  and axle torque rate). This confounds the
  observations in terms of isolating which input(s)
  caused the apparent result.
• The net result is that people just dont do very
  well in learning about the wheel when on their
  own.

6
Design Solution

• This seems like a very ripe opportunity for
  exactly an Exploratorium hands-on approach to
  help visitors develop some sort of physical
  intuition about wheel dynamics. If we can go
  even further and actually teach people how and
  why wheels behave so unexpectedly, then visitors
  can leave with some real world knowledge that
  connects with every day experience.
• The following pages illustrate several new
  exhibits which are designed to follow the
  Exploratoriums hands-on style of learning and to
  allow visitors to gain some intuitive and
  intellectual comprehension of wheel dynamics.
  They are ordered from least expensive and easiest
  to implement to most expensive and involved.
• Proposed new exhibits
• 1) New explanation of wheel dynamics
• 2) The Precession Pendulum - Wheel hung as a
  pendulum
• 3) The Interactive Wheel Quiz
• 4) Wheel and Gyroscope Laboratory

7
The Wonder of Wheels - Whats Happening
A spinning wheeland its parts
8
The Precession Pendulum
rigid rod and rigid connection so that the entire
wheel apparatus is suspended from the ceiling and
acts as a giant pendulum
collar and tightening nut which allow wheel axle
to be angled to horizontal
focused light source shining as a spot on the
floor so that it is easy to see exactly what path
the wheel traces out as it swings
lines drawn on floor underneath apparatus to help
visitors discern the curve motion of the wheel as
it precesses
9
How Well Do You Know Your Bicycle Wheel?

• This is a multiple choice quiz displayed on a
  large screen. Visitors should use the
  free-standing wheels to see if they can figure
  out which are the correct answers. Assume that
  the wheel is held in one hand and is spinning in
  a clockwise direction when answering the
  questions.

1. What will happen if you hold a wheel axle with
one hand, spin the wheel clockwise, and you twist
upwards with the wrist that is holding the
axle? 2. What will happen if you move the wheel's
axle parallel to itself (i.e., left/right or
up/down without twisting the axle)? 3. What will
happen if you just hold the wheel's axle at a
45-degree angle to the horizontal? 4. What will
happen if you attach a rope to one side of the
wheel to hold it up? 5. What will happen if you
suspend the wheel by using a rope that attaches
to both sides of the wheel 6. (Follow-up to
previous question) What happens if the wheels
axle is not quite parallel to the horizontal? 7.
What happens if you twist your wrist (and the
axle) upwards while spinning the wheel faster
versus slower? 8. (Follow-up to previous
question) Or if you spin it clockwise versus
counter-clockwise? 9. Draw a line that
represents the motion described by the end of the
axle if you gently sweep your hand horizontally
back and forth, bending only at the wrist? 10.
What happens if you quickly twist the axle, say
by flexing your wrist upwards, versus doing so
more slowly versus doing it very slowly?
10
Wheel and Gyroscope Lab
Display and keyboard. This provides measurement
readouts and guides visitors through various
games and experiments to do with the wheel
apparatus
second wheel which can be attached to armature to
counterbalance and counter-spin the other wheel
spindle which allows wheel armature to freely
move in horizontal and vertical directions
sensor which measures wheel rotation rate
collar and tightening nut which allow wheel axle
to be angled to horizontal
sensor which measures wheel spin rate
sensor heads which measure precession rate,
precession angle, pitch angle, and pitch change
rate
slidable and removable counterbalancing weights
wiring connecting display with instrumentation
base containing instrumentation electronics