FOR MORE OF THIS COURSE AND ANY OTHER COURSES, TEST
BANKS, FINAL EXAMS, AND SOLUTION MANUALS
CONTACT US
The Student-Centered Class
A great lecture is one where central information is concise and
clearly explained, and when appropriate, with demonstrations. The students
value such a lecture because clear explanations are what they are there for. A
not-so-great class is one where the instructor covers peripheral information,
not central, and not clearly explained. Poorly executed demonstrations do
little to make the fix. Either way, in traditional
classes where lectures are the main focus, the students remain seated with pen
and paper taking notes to be studied in more detail later.
The
traditional class format can be effective, at least if we are looking at
short-term goals. Educational research suggests, however, that better results
are obtained when the instructor makes the students active participants.
Check-Your-Neighbor type questions are a good starting point for active
participation. This is where you as the instructor ask a question of the class
and students discuss possible answers amongst themselves.
You
can take this interactive approach a step further by allowing students to use
class time to collaborate on projects, worksheets, or hands-on activities.
Collaborative, student-centered learning can be achieved through various
teaching strategies. For example, students can be asked to do the science
demonstrations themselves and asked to explain the underlying concepts. Any
lecture presentation you provide can be short and sweet, and provided “on the
fly” in response to students’ specific needs as revealed by the demonstrations.
In such a scenario, students are in the spotlight. They find that class is akin
to a grand study session where the instructor is their study leader, who
migrates from team to team providing expert assistance on demand. This is the
essence of the “student-centered” class. Lectures are minimized for the sake of
increased class participation.
Students
Must Come Prepared
The prerequisite to an effective
student-centered class is that the student arrives to class prepared.
Assignments need to have been read beforehand
and exercises attempted beforehand
such that a hazy understanding has already begun to take form. But as any
instructor knows, student resistance to coming to class prepared can be
intense. How then do we motivate students to come to class prepared? There are
numerous tools. First of all, it is vital that the textbook be as user-friendly
as possible—students should enjoy reading it! This, of course, has been one of
the main goals in developing the Conceptual
Integrated Science textbook. The student should be able to learn about
science concepts on his or her own with minimal assistance from the
instructor—and it should make good reading! This, in turn, supports the
instructor who is wishing to move toward a student-centered class.
Another
important tool for encouraging students to study is a short quiz given at the
beginning of class, or even before
class with the quiz posted on the course website. This quiz should assess
students for their familiarity, not their expertise, of the material about to be
covered. Following the quiz and a brief introduction, students work on various
activities within teams. If a student comes ill-prepared, he or she then faces
the motivating factor of peer pressure.
Of course, not everyone can always come prepared. Students know this and
are generally forgiving and welcoming of all input either weak or strong. So
peer pressure needn’t be unkind.
If you are
ready to make your classes more student-centered, you need to let your students
know at the beginning of the semester how this approach will help their
learning, provide for an enjoyable experience, and, ultimately, improve their
test scores. Notably, the interpersonal skills gained through collaborative
learning is an added plus. Also, students are much more willing to participate
if the in-class activities are unequivocally related to the quizzes and exams
they take.
Lastly, a
student-centered approach consumes a large portion of class and so the
instructor has less opportunity to deliver content, though a greater opportunity
to facilitate the learning of content. Consequently, in order to keep pace with
a traditional syllabus, the instructor needs to decide whether there will be
material on exams not covered directly in class. If so, the instructor should
be mindful to reserve class time for the more challenging concepts.
Students
Are the Players and You Are Their Coach
There
is great pedagogical potential in transforming a class from passive learning to
active, student-centered learning. To achieve the potential, what is needed is
a willingness to get creative and to push the responsibilities of learning more
squarely on the student. The role of the instructor is to provide students with
good questions rather than good answers. We can think of students as team players
out on the field doing all the hard work, which means finding answers for
themselves. We are their coaches here to direct their learning efforts.
Sometimes the best way to do this is by knowing when to cheer and when to
remain silent.
Getting
Started
So, is it better to retool one’s teaching
methods in a single semester or to explore new activities one at a time over
many years? Revolution or evolution? If you’re like most of us, the thought of
revamping everything within a single semester is most undesirable. Indeed,
implementation of any student-centered activity requires a fair amount of trial
and error. Imagine implementing many new activities all within a few weeks only
to have them fail miserably. This would be a disservice to your students and to
yourself. The best practice is to introduce only the activities you think will
work in a time frame that allows for successful development.
The
techniques presented here are a select few that we authors know work well. Some
work for large classes while others are better suited for smaller classes.
Chances are that you have already implemented techniques of your own or that
new ideas will soon be coming to you as you forge ahead. Also, you need look no
further than journals, such as those of the National Science Teachers
Association or through the web to find a constant flow of student-centered
learning innovations. Some references are included at the end of this essay.
The point to be made is that student-centered learning can be implemented
profitably even by teachers who have had great success with lecturing.
Student-Centered Assessment
Techniques
(What students can do to
articulate what they think they’ve learned)
We
give homework, quizzes and exams so that we can provide students with a grade.
But there is another important reason for these assessment tools, which is to
provide students with feedback on their learning. Interestingly, assessment and
grading need not be paired. So if you’re looking for a stress-free,
non-penalizing way to support your students as they struggle to learn, consider
providing “suggested homework”, “practice quizzes”, “practice exams”, and even
“practice worksheets”. To show you appreciate the great value of practice (as
would any coach, including an academic coach), let your students do these
practice activities right during class where you’ll be personally available to
offer assistance to individuals and to teams. Students appreciate the
opportunity to practice, which is why we say: assess often, grade only when
needed.
The Concepts Inventory
The
Concepts Inventory is a short test taken by students at the beginning of the
semester and definitely not graded. In fact, you might consider having the
students take the test anonymously. At the end of the semester, the Concept
Inventory with the very same questions is given again to provide a
semi-objective measure of overall student learning. This is an assessment not
only of the students but of the course as well. Inventory questions should
reflect concepts that you hope the students will learn by taking the course. A
good inventory will also include questions that address common
misconceptions. Rather than giving the
inventory again at the end of the semester, you might consider sneaking the
questions (some or all) into the final exam.
EOC Exams
At the end of
each chapter (EOC) of Conceptual
Integrated Science are numerous questions. These are provided so that
students can practice applying the concepts they think they have learned. But
of course, many students tend not to work on these questions unless they are
assigned by the instructor for homework, usually just a selected few. As an
alternative, students can be given a longer list of each of the instructor’s
favorite EOC questions that are applicable to the course syllabus. The students
are then told that a certain number of these questions will definitely be
posted on an upcoming exam. Keep in mind that only the answers to the
odd-numbered EOC questions appear at the back of the textbook. Also, many of
these EOC questions can be found in multiple-choice format within the Conceptual Integrated Science test bank.
The Minute Quiz
As said, a quickie quiz given at the beginning
of class it is a valuable component of your course. Their purpose, as said, is
to motivate reading material for the day before class. Call them “minute
quizzes” because the students have only one minute to answer a question that
calls for a word or very short sentence. They can pass their quizzes to the
front of the room, or put into boxes passed around the class. If you have the
time and motivation to grade and record responses, good for you. But as said,
even if you tell the class that you’ll not look at every day’s quizzes, and you
won’t record scores, the process still works! Students don’t like handing in
blank papers!
The Two Minute Quiz
The minute quiz described above can be extended
in to two phases. For the first phase, students get about a minute to answer
the question, which may be printed on a narrow strip of paper. They can put their
answers into a box that gets passed around the class. A right answer is worth,
say, 25 points while a wrong answer is worth 10 points. A student, however, may
opt not to put his or her quiz into this box and may instead hold onto the quiz
until the second phase, which begins when students are told they can now open
their notes, their textbooks, and talk with their neighbors about the possible
answer. After another one minute period they place the quiz into a second box,
which means they get, say, 20 points for a right answer and 15 points for a
wrong answer. Students soon to catch onto the best strategy, which is to wait
for the second round if they’re not sure of the answer.
The Importance of Fairness in Exams
There
should be no big surprises on an exam. Students should know what to expect,
which is coverage of course topics, with question difficulty that finds your
top students getting perfect or near-perfect scores. Your fairness as an
instructor is judged by the fairness of your exams. Exams that cover what
students expect are fair. Exams wherein top students excel also display your
sense of fairness. How discouraging for students when class averages are so low
that your not being on target moves you to play God at semester’s end and grade
on the curve. Please read Paul Hewitt’s history of teaching and how he handled
exams to lure more than a thousand students to his non-required conceptual
physics course at City College of San Francisco in the October 2011 issue of
The Physics Teacher.
Collaborative Exams
For a significant
learning experience, an exam may be offered in three phases: individual, team,
and class. In the first phase each student takes the exam individually while
also filling out a duplicate exam (or Scantron) that contains their answers but
not their name. Assessment for this individual effort should be weighted the
greatest. For example, each question may be worth 5 points, while for the
second phase each question is worth 3 points, and for the third phase just 1
point.
A ten-minute warning is given to
assure that all students finish with the first phase at about the same time.
Exams are turned in while the duplicate student answers are spread out onto a
broad table. Students then congregate into their teams to take the exam again,
but this time working together and with resources, such as the textbook. They
are also permitted to send a scout to inspect the duplicates to see how the
rest of the class answered specific questions. Each member of the team should
have a copy of the exam, but only one exam is to be turned in for assessment.
Meanwhile, the instructor and/or TA is quickly grading the individual exams.
(Use a Scantron if available.) The goal is to post the class average before the
teams finish their team exams. This feedback allows teams to gauge the value of
the displayed duplicates. A quick alternative to grading all the exams is to
post the average score of five random individual exams.
After teams turn in their team
exams they are ready for the third phase in which they take the exam yet again
together as a class. The instructor records their answers on a single master
copy of the exam. Teams vote for an answer by holding up color-coded flash
cards. Teams are allowed to argue their answers, but majority wins. If there is
a tie among teams, then there is a recount after some healthy debate. After
each class answer is recorded students are then told the correct answer, which
is often followed by cheers or groans.
The
length of the exam is determined by the duration of the class. For a 75-minute
class, the exam can contain up to 25 questions. For 50-minute class, the exam
should be narrowed down to about 15 questions. Timing is an important factor.
In particular, students should finish the first phase all at about the same
time. Slower students can be encouraged to come to class early for a head
start. It is also helpful to have a second room where slower students can go in
the event they need another 5 or 10 minutes to finish the first phase while
their team move ahead. For the second phase, which is the team phase, it helps
to include a “toughie” bonus short-essay question at the end of the exam. This
is useful for teams who finish early—it keeps them busy while other teams are
still working on the regular questions. There is not always sufficient time to
have the third phase, which is when the class takes the exam together as a
whole. To expedite the third phase, the instructor lays out the team answers so
he or she can see all the team answers at a glance. Instant credit is given to
questions that are unanimously correct. This allows the instructor to move on
to some of the more difficult questions, which tend to have different answers
from different teams.
By the time the class period
is over, students have taken the exam three times and know their final score.
Individual effort is preferentially rewarded, yet students still get the
valuable experience of working together as a team. Furthermore, with such a
format, the instructor can include challenging questions that may foil many
individuals but not many teams. The individual phase of the exam may average 65
percent or less. This is balanced, however, by the team and class phases, which
may run 80 percent and 95 percent, respectively, so that the overall average is
within the mid-70’s. One drawback to this format is that it consumes a lot of
paper. If each student has access to a computer, however, the paper can be
replaced by online delivery, which would also assist with the instant grading
that makes this activity so effective.
Appeals
With
end-of-semester course evaluations, a number one concern shown by most students
is whether or not the course was fair. Toward satisfying this need, students
may be permitted to appeal any question for which they believe they deserve
credit. The instructor sets up the conditions of the appeal. For example, the
student’s explanation for why they think they deserve credit must be
hand-written and submitted within a certain time frame. Also, only those who
were actively involved in the appeal, as indicated by their signature, have the
possibility of gaining points. Appeals are reviewed by the instructor in the
safety of his or her home or office where he/she may assign full, partial or no
credit. Aside from providing students a sense of fairness on your part, the
appeals provide the feedback you need to modify questions that might not be
worded optimally. We should underscore that students really appreciate the
opportunity to appeal, as will become evident on your course evaluations.
Student-Centered Learning
Activities
(What students can do when
the instructor is not lecturing)
Team Formations
Collaborative
learning tends to work best when students are grouped together in teams
consisting of either 3 or 4 students. For a team of 5 students, invariably, the
fifth student takes a back seat and is less involved. For a team of 2 students,
there is not a sufficient diversity of ideas. Who goes on what team is the
difficult responsibility of the instructor who knows that each team needs to be
well-balanced in terms of academic abilities and gender. At the start of the
semester, the instructor can eye-ball who goes where. Putting friends initially
together is a good thing. Alternatively, the instructor can await the results
of a Concepts Inventory and use student scores as the basis for team
formations.
The instructor should consider new team
formations after each exam. Students thus work together in the same team on up
to the next exam, which is collaborative as described earlier. Exam scores are
then used as the basis for new team formations.
The first assignment of any team is to
agree upon a team name. The periodic table provides a wealth of possibilities.
Team Titanium, Team Gold, and Team Einsteinium are some of the more popular
choices.
Hands-On Science
Within each
chapter of Conceptual Integrated Science
are home-project type activities. These brief activities are most conducive to
team learning in the classroom. As you can imagine, students appreciate the
hands-on exploratory nature of these activities—they really help to liven up a
class. The drawback is the time it takes to make sure that each team is set up
with the proper materials, and to make sure that students clean up after
themselves. We need not restrict all lab activities to the lab when there are
so many small, safe, easy-to-set- up activities that can also be done
effectively in class.
An important ancillary is Suzanne Lyons book, “Minds On Hands On,”
loaded with intriguing activities and more. This ancillary is especially
important to the instructor new to teaching the wide swath of Conceptual Integrated Science.
Practice Pages
An important
supplement to Conceptual Integrated
Science are the Practice Pages, which are a set of minds-on concept review
worksheets. The Practice Pages are designed as a study aid that students can
work on outside of class. They are far more effective, however, when students
work on them together as a team under the expert supervision of the course
instructor, who travels from team to team to assist students as necessary. It
is common that a Practice Page will prompt a question from a student that, in
turn, prompts the instructor to give a short lecture presentation to the team.
In such instances, neighboring teams can be encouraged to eavesdrop. This is
known as “targeted teaching” and it arises as the instructor roams about the room
checking on team progress. Occasionally, it prompts the instructor to switch
gears and give his or her mini-presentation to the whole class. Targeted
teaching is impromptu and in response to immediate student need.
Think-Pair-Share
This technique was made popular by Eric Mazur
of Harvard University
Readiness
Assurance Test (RAT)
Hands down, this is the student’s favorite
activity—not for the joy of it but because it is most related to helping him or
her perform well on exams. The RAT is simply a trial exam given before the
actual exam. It helps students assess how ready they may or may not be for the
exam. Everything about the RAT should be identical to the exam except that the
points don’t count and the questions are different!
You
will find that there are short RATs already given at the end of each chapter.
You might consider building your RAT using these questions. Alternatively, if
you formulate your own RAT questions, you might consider using some of the
textbook’s RAT questions for your exam to reward students who have been working
with the questions at the back of each chapter.
But
in implementing a RAT you will come across a deep question, which is “Should
you offer a RAT during a class before an exam when this means losing a day of
instruction?” If you use the “collaborative exams” technique described earlier,
then you will quickly come to find that you are by no means “losing a day of
instruction” when you implement a RAT.
Rather, you are helping your students to solidify their understanding of
science, which may be an important aspect of your job description.
Does implementing a RAT mean you will need
to cut back on topics normally covered in your syllabus? Not necessarily. Some
students actually learn well by reading the textbook. Others prefer watching
the textbook authors deliver their “talking textbook” video lessons at
ConceptualAcademy.com (Please check us out!). All students will appreciate
solidifying their understanding of these topics (such as rainbows, nuclear
physics, natural selection, the rock cycle or the solar system) in class under
your expert guidance. The RAT is a good vehicle for this purpose.
Class Presentations with Activity Intervals
Select questions are assigned to teams of
students who then have a short period of time (10 minutes) to prepare and
practice articulating an answer. Students as individuals or as a team then get
up in front of the class to articulate their answers in a short two-minute
presentation. They then ask the class if there are any questions. The
instructor, meanwhile, has planted some well-thought-out questions among the audience
who then ask these questions, which probe deeper into the concepts. The
presenting student or students can either respond or choose to serve as
moderators of a class discussion.
Certain questions lend
themselves to short but effective hands-on activities. After a student
presentation on surface tension, for example, the class can be challenged to
float a paperclip on water. Or after a presentation on condensation, the
instructor can invert a steam-filled soda can in water. Students are then
prompted to explain why the can imploded. Of course, if they can’t figure it
out, it is the responsibility of the instructor to keep quiet or provide only
hints.
Questions that
work well for this technique include the Think and Explain questions from the
textbook. These questions also lend themselves well to study group sessions
either outside of class or during class. A student should be reminded that if
he or she understands the answer to one of these questions—if he or she really
does—then he or she should be able to articulate the answer (verbally!) to
someone else, such as a fellow student. Note: Isn’t this remindful of when we
learned most about a subject: when we articulated it to others?
Focused Listing
On a blank
sheet of paper, students write down a list of 4 or 5 terms or phrases that
summarize the content of a textbook section or reading assignment. This
activity quickly assesses what key concepts were difficult for the student to
understand. A related activity described by Angelo and Cross is called “The Muddiest
Point” whereby students write down concepts from a chapter that were most
unclear. The instructor then uses this information to launch a class
presentation (mini-lecture or demonstration) or a class discussion à la the
Socratic method whereby everything the instructor says is phrased as a
question.
Reward Race
A set of not-so-easy multiple choice questions
are posted around the room. Students work in teams to answer these questions.
The first team to get all answers correct wins the prize, preferably something
made of chocolate. Strategies are important. Some teams will decide to split
up. Others will stay huddled as they migrate from one question to the next.
Also, if a team submits answers but gets at least one wrong, they are not
allowed to submit answers again until either all the other teams have had a
chance or after a specified amount of time. Furthermore, the instructor does
not tell teams which questions they got wrong, only the number of them they got
wrong. This is certainly one of the more fun activities.
Office Visits
While the class is occupied with some learning
activity (pensive activities, such as the Practice Sheets are best), the
instructor pulls individual students away for a required brief office visit.
The instructor inquires about how things are going and whether the student has
any general or specific questions or concerns. This is also a good time to show
the student his or her present course grade and provide advice on how to do
well in the course. Furthermore, this activity serves as an important ice-breaker
that makes students more inclined to visit you outside of class.
Field Trip
Class-size permitting, take students on a tour
of any science research laboratories near you. Ask your colleagues and
University researchers whether they would be willing to talk to your students
about why they like science and why they chose it as a profession.
The Conceptual Café
Bring in a stack of recent science journals,
both popular and technical, and set the classroom up as though it were a coffee
house—quiet background music, tea, donuts, etc. Students merely spend the class
time reading through these journals and discussing science-related topics with
their peers as well as the instructor. Few, if any, students will likely have
looked through a rigorous technical journal, such as the Journal of the American Chemical Society. These journals can be
intimidating for their detail, especially the experimental sections. But
students should have some first hand experience at the utterly vast amount of
information that has been generated and is being generated by scientists around
the world. After looking at the technical journals, students will find the
popular science magazines to be a breath of fresh air. It’s likely that most of
your students have never read through a popular science magazine. Perhaps, down
the road this activity will help them to think twice about throwing away one of
those pervasive science magazine subscription offers.
Instructor-Centered Learning
Activities
(What the instructor can do
outside of class)
Class Journal
Student-centered learning is such fertile ground for
educational innovation. As soon as possible after class, we encourage you to
open up your Class Journal and start recording what went well and what went
wrong. We can almost guarantee that through this process ideas for improvements
will arise. The process of writing in your journal, especially soon after
class, is a great way to allow these ideas to come to the surface where you can
consider them in fuller detail.
Think-Pair-Share
Try Think-Pair-Share with your colleagues. First, think about your curriculum using your
class journal. Discuss your experiences and ideas with your colleagues. Then
share your ideas with others through departmental seminars or regional or national
meetings. The key word here is synergy.
We instructors don’t work in a vacuum. In working together we can fast-forward
to better ways of reaching our non-science oriented students.
Explore References
Here are a few references about student-centered learning techniques.
Thomas
A. Angelo, K. Patricia Cross, Classroom
Assessment Techniques, A Handbook for College Teachers, 2nd ed.,
Jossey-Bass, 1993.
Eric
Mazur, Peer Instruction: A User’s Manual,
Prentice-Hall, 1997.
Jeffrey
P. Adams, Timothy F. Slater, Strategies
for Astro 101, Prentice-Hall, 2003.
Chemical
Concepts Inventory
http://jchemed.chem.wisc.edu/JCEDLib/QBank/collection/CQandChP/CQs/ConceptsInventory/CCIIntro.html
or
just type: “Chemical Concepts Inventory” into Google.
Collaborative
learning activities
www.wcer.wisc.edu/nise/cl1/cl/
Field-Tested
Assessment Guide (CATs)
www.flaguide.org
Just
in Time Teaching
www.JiTT.org
Process
Oriented Guided Inquiry Learning (POGIL)
www.POGIL.com
“The
Missing Essential — A Conceptual Understanding of Physics” Paul Hewitt’s
Millikan Award talk, American Journal of Physics, January 1983.
Some Teaching Tips
•
Attitude toward students and attitude about science in general is of utmost
importance: Consider yourself not the master in your classroom, but the main
resource person, the pacesetter, and the guide. Consider yourself a bridge
between your student’s ignorance and some of the information you’ve acquired in
your study. Guide their study—steer them away from the dead ends you
encountered, and keep them on essentials and away from time-draining
peripherals. You are there to help them. If they see you so, they’ll appreciate
your efforts. This is a matter of self-interest. An appreciated teacher has an
altogether richer teaching experience than an under-appreciated teacher.
•
Don’t be a “know-it-all.“ When you don’t know your material, don’t pretend you
do. You’ll lose more respect faking knowledge, than not having it. If you’re
new to teaching, students will understand you’re still pulling it together, and
will respect you nonetheless. But if you fake it, and they CAN tell, whatever
respect you’ve earned plummets.
•
Be firm, and expect good work of your students. But be fair and get papers
graded and returned quickly. Be sure the bell curve of grades reflects a
reasonable average. If you have excellent students, some should score 100% or
near 100% on exams. This way you avoid the practice of fudging grades at the
end of the term to compensate for off-the-mark low exam scores. The least
respected professor in my memory was one who made exams so difficult that the
class average was near the noise level, where the highest marks were some 50%.
•
Be sure that what knowledge you want from your students is reflected by your
test items. The student question, “Will that be on the test?“ is a good
question. What is important—by definition—is what’s on the test. If you consider
a topic important, allow your students credit for their feedback on that topic.
An excellent student should be able to predict what will be on your test.
Remember your own frustration in your student days of preparing for a topic
only to find it not part of the test? Don’t let your students experience the
same. Many short questions that fairly span course content is the way to go.
•
Consider having students repeat work that you judge to be poor—before it gets a
final grade. A note on a paper saying you’d rather not grade it until they’ve
given it another try is the mark of a concerned and caring teacher.
•
Do less professing and more questioning. Information that is of value ought to
be the answer to a question. Having frequent “check-your-neighbor“ intervals
should be an important feature of your class. Their feedback to you can be
immediate with the use of student whiteboards, or their electronic
counterparts. Beware of the pitfall of too quickly answering your own
questions. Use “wait-time,“ where you allow ample time before giving the next
hint.
•
Show respect for your students. Although all your students are more ignorant of
physics than you are, some are likely more intelligent than you are.
Underestimating their intelligence is likely overestimating your own. Respect
is a two-way street.
1 About Science
1.1 A Brief History of Advances in Science
1.2 Mathematics and Conceptual Integrated
Science
Math
Connection: Equations as Guides to Thinking
1.3 The Scientific Method—A Classic Tool
1.4 The Scientific Hypothesis
1.5 The Scientific Experiment
1.6 Facts, Theories, and Laws
Science and
Society: Pseudoscience
1.7 Science Has Limitations
1.8 Science, Art, and Religion
1.9 Technology—The
Practical Use of Science
1.10 The Natural Sciences: Physics, Chemistry,
Biology, Earth Science, and Astronomy
1.11 Integrated Science
Integrated
Science—Chemistry and Biology: An Investigation of Sea Butterflies
A common practice is spending the first week of a
science class on the tools of science—unit conversions, significant figures,
making measurements, and using scientific notation. This is anything but
exciting to most students. The authors of this book believe that this is
pedagogical folly. How much better it is if the first week acts as a hook to promote
class interest, with tools introduced if and when they are needed later in the
course. So, this book begins by introducing the nature of science, the value of
integrated science, the scientific method, the role of science in society, and
other topical issues such as pseuodoscience, the relationship between science
and religion, and the similarities and differences among science and art.
Screen casts on the web, “Hewitt drew it”:
Although there’s no cast particularly for this
chapter, Hewitt’s passion for physics is nicely treated in the first Screencast
#1; The Equilibrium Rule.
In Next-Time
Questions:
• Hypotheses
In the Lab
Manual:
• Tuning
the Senses (enhancing perception)
• Making
Cents (introduces the mass balance and the making of a simple graph)
Suggested Presentation
A Brief History of Advances in Science
Science is organized knowledge. Its roots are found
in every culture. The Chinese discovered printing, the compass, and rockets;
Islamic cultures developed algebra and lenses; mathematicians in India
While early Greeks, in an era of experimental
democracy and free thinking, were questioning their speculations about the
world, their counterparts in the more authoritarian eastern parts of the world
were largely occupied in absorbing the knowledge of their forebears. In regions
like China Eurasia .
In any event, it is important to emphasize throughout your course that all science is a human endeavor. In addition
to being a legacy of what humans have learned about nature, it’s also a human
activity that answers questions of human interest. It is done by and for humans.
You may consider elaborating the idea that the test
of correctness in science is experiment. As Einstein once said, “many
experiments may show that I’m right, but it takes only one experiment (that can
be repeated) to show that I’m wrong.” Ideas must be verifiable by other
scientists. In this way science tends to be self-correcting.
Mathematics and Conceptual Integrated Science
The mathematical structure of science is evident in
this book by the many equations. These are shorthand notations of the connections
and relationships of nature. They are seen primarily as guides to thinking, and
only secondarily as recipes for solving problems. Many instructors bemoan
students who reach for a formula when asked a scientific question. We authors
take a more positive view of this, for formulas are shorthand statements about
the connections of concepts. For example, if asked if speed affects the force
of gravity on earth satellites, a look at the equation for gravitation tells us
no—only mass and distance affect
force. Now if speed changes the distance, then in that case, yes. When
equations are seen as guides to thinking, then conceptual thinking is present.
Hooray!
You can provide a specific example of “equations as
guides to thinking” by going over the Math Connection box. This feature is
meant to clarify the role of math in Conceptual
Integrated Science rather than to challenge students. The notions of direct
and inverse proportions are intuitively easy to grasp—showing that science
often has a mathematical structure, but this structure need not be difficult to
grasp.
The Scientific Method—A
Classic Tool
The scientific method is given in a six-step form.
We say that science is structured common sense. The scientific method is an
example. The scientific method is to be seen as a sensible way to go about
investigating nature. Although the six steps are useful, they don’t merit your
students memorizing them. And most often, they are not the specific steps used
in scientific discoveries. The scientific
attitude, more than a particular method, underlies scientific discovery.
A
Scientific Attitude Underlies Good Science Expand on the idea
that honesty in science is not only a matter of public interest but is also a
matter of self-interest. Any scientist who misrepresents or fudges data, or is
caught lying about scientific information, is ostracized by the scientific
community. There are no second chances. The high standards for acceptable
performance in science, unfortunately, do not extend to other fields that are as
important to the human condition. For example, consider the standards of
performance required of politicians.
Scientific Hypotheses
Distinguish between hypothesis, theory, fact, and concept. Point out
that theory and hypothesis are not the same. A theory applies to a synthesis of a large body of information. The
criterion of a theory is not whether it is true or untrue, but rather whether
it is useful or not. It is useful even though the ultimate causes of the
phenomena it encompasses are unknown. For example, we accept the theory of
gravitation as a useful synthesis of available knowledge that relates to the
mutual attraction of bodies. The theory can be refined, or with new
information, it can take on a new direction. It is important to acknowledge the
common misunderstanding of what a scientific theory is, as revealed by those
who say, “But it is not a fact; it is only
a theory.” Many people have the mistaken notion that a theory is tentative or
speculative, while a fact is absolute.
Impress upon your class that a fact is not immutable and absolute, but it is generally a close
agreement by competent observers of a series of observations of the same
phenomena. The observations must be verifiable. Because the activity of science
is the determination of the most probable, there are no absolutes. Facts that
were held to be absolute in the past are seen altogether differently in the
light of present-day knowledge and observational equipment.
By concept,
we mean an intellectual framework that is part of a theory. We speak of the
concept of time, the concept of energy, or the concept of a force field. Time
is related to motion in space and is the substance of the Theory of Special
Relativity. We find that energy exists in tiny grains, or quanta, which is a
central concept in the Quantum Theory. An important concept in Newton
Prediction in science is
different from prediction in other areas. In the everyday sense, one speaks of
predicting what has not yet occurred, like whether or not it will rain next
weekend. In science, however, prediction is not so much about what will happen, but about what is happening and is not yet noticed,
like what the properties of a hypothetical particle are or are not. A scientist
predicts what can and cannot happen, rather than what will or will not happen.
Science Has Limitations
Just as a great strength of a democracy is its
openness to criticism, likewise with science. This is in sharp contrast to
dogma, which is seen as absolute. The limitations of science, like those of
democracy, are open for improvement. The world has suffered enormously from
those who have felt their views were beyond question. Author K. C. Cole says it
well when she asserts that belief in only one truth and being the possessor of
it is the deepest root of all the evil that is in the world.
Pseudoscience
The material on pseudoscience should be excellent
for student discussions. A stimulating exercise is to ask students to formulate
a series of questions that help determine whether a given claim is a case of
pseudoscience. Such a list might include the following questions, and more:
• Does the
claim use technical-sounding jargon that is not precisely defined?
• Does the
claim use scientific words imprecisely and in a nonscientific context (e.g.,
“energy,” “frequency,” “vibration”)?
• Do
proponents complain of being overly criticized?
• Is one
reason given for the supposed validity of the claim that it has been around a
long time (so it must be true)?
• Do
proponents of the claim use the logical fallacy of the ad hominum to respond to
critics? (An ad hominem argument is a challenge directed at he who expresses an
idea rather than at the idea itself.)
Pseudoscience is very big business, and examples of
it abound. Help students understand the difference between nonscience, science,
pseudoscience, and protoscience (a
new science trying to establish legitimacy).
The Search for Order—Science,
Art, and Religion
Einstein said, “Science without religion is deaf;
religion without science is blind.” The topic of religion in a science text is
rare. We treat it briefly only to address what is foremost on many students’
minds. Do religion and science contradict each other? Must one choose between
them? We hope our very brief treatment presents a satisfactory answer to these
questions. Our take is that religion and science are compatible when they
address different realms. When the certainty often associated with particular
religions spills over into science, then there is an unfortunate
incompatibility between religion and science.
Technology—Practical
Use of the Findings of Science
In discussions of science and technology and their
side effects, a useful statement is: You
can never do just one thing. Doing this
affects that. Or, You can never change only one thing. Every time you
show an equation, it’s evident that changing a variable on one side of the
equation changes one or more on the other side. This idea is nicely extended
with “there is never just one force” in discussions of Newton
The Natural Sciences: Physics, Chemistry, Biology, Earth
Science, and Astronomy
With regard to science courses and liberal arts
courses, there is a central factor that makes it difficult for liberal arts
students to delve into science courses the way that science students can delve
into liberal arts courses—and that’s
the vertical nature of science courses.
They build upon each other, as noted by their prerequisites. A science student
can take an intermediate course in literature, poetry, or history at any time.
But in no way can a humanities student take an intermediate physics or
chemistry course without first having a foundation in elementary physics and
mathematics. Hence the importance of this conceptual course.
Integrated Science
Coming into this course, students may be hazy about
what integrated science is. Yet, once you explain it to them, they will readily
grasp the value of it. When asked “Why study integrated science?” one student
simply stated “Because life is integrated.” We fully agree. Point out to
students that they will see over and over in this text—and in their everyday lives—that
the branches of science are interconnected. How can one understand the host of
interesting and important scientific phenomena—from
global warming to the origin of the solar system to forensic medicine—without integrating concepts from
different branches of science?
An Investigation of Sea
Butterflies This
case study examines the scientific method as actually applied as well as
provides a specific example of integrated science. Another important point
discussed is the idea of a scientific control—a basic feature of a valid
scientific experiment. This idea can be rather subtle, so you may want to
emphasize it in your lecture. Consider using the concept check questions for
this feature as check-your-neighbor questions—they
get at the main ideas of this section.
2 Describing Motion
2.1 Aristotle on Motion
2.2 Galileo’s Concept of Inertia
History of
Science: Aristotle
History of
Science: Galileo
2.3 Mass—A
Measure of Inertia
2.4 Net Force
2.5 The Equilibrium Rule
Science and
Society: Paul Hewitt and the Origin of Conceptual Integrated Science
2.6 The Support Force
Math
Connection: Applying the Equilibrium Rule
2.7 Equilibrium of Moving Things
2.8 The Force of Friction
Integrated
Science—Biology, Astronomy,
Chemistry, and Earth Science: Friction Is
Universal
2.9 Speed and Velocity
2.10 Acceleration
Integrated
Science—Biology: Hang Time
Demonstration Equipment
Coat hanger and clay blobs
Wooden block stapled to a piece of cloth (to
simulate tablecloth pull)
Tablecloth (without a hem) and a few dishes (for the
tablecloth pull)
Piece of rope for a classroom tug-of-war
Wooden cube that will fit on a pan balance (another
material such as cardboard will do)
Pan balance
This chapter introduces students to kinematics and dynamics. Kinematics is the study of
motion without regard to the forces that produce it. When forces are
considered, the study is then of dynamics. The authors believe that one of the
great follies of physics instruction is overtime on kinematics. Whereas many
physics books begin with a chapter on kinematics, this is downplayed in this
book. We treat only the amount of kinematics needed, mainly distinguishing
between velocity and acceleration as a launching to Newton Newton
Of particular interest to me (Hewitt) is the
Personal Essay in the chapter, which relates to events that inspired me to
pursue a life in physics—my meeting
with Burl Grey on the sign-painting stages of Miami , Florida
So force, rather than kinematics, is the emphasis of
this chapter. And force vectors, only parallel ones at this point, are the
easiest to understand. They underlie the equilibrium rule: SF = 0 for systems in
equilibrium. These are further developed in the Practice Book. (Not using the Practice
Book is like teaching swimming away from water. This is an important book—the authors’ most imaginative and
pedagogically useful tool for student learning!)
Note that in introducing force, we first use pounds—most familiar to your students. A quick
transition, without fanfare, introduces the newton. We don’t make units a big
deal and don’t get into the laborious task of unit conversions, which is more
appropriate for physics majors.
A brief treatment of units and systems of measurement
is provided in Appendix A.
If you get deeply into motion, you can consider the Sonic Ranger lab, which uses a sonar
ranging device to plot in real time the motion of students, rolling balls, or
whatever. This lab can be intriguing, so be careful that it doesn’t swallow too
much time. Again, overtime on kinematics is the black hole of physics teaching!
Screen casts on the web, “Hewitt drew it”:
• 1. The
Equilibrium Rule
• 2.
Equilibrium Problems
• 3. Net
Force and Vectors
• 4.
Nellie’s Rope Tensions
• 5.
Nellie’s Ropes
• 7. Force
Vectors on an Incline
• 8. Linear
Motion Definitions
• 9. Bikes
and Bee Problem
• 10. Unit
Conversion
• 11.
Velocity Vectors
• 12. Free
Fall
• 18.
Acceleration Units
In the Practice
Book:
• Vectors
and Equilibrium
• Free Fall
Speed
• Acceleration
of Free Fall
In Next-Time
Questions:
• The
Scaffold in Equilibrium
• The Bee
and the Bicycle
In the Lab
Manual:
• Go Go Go!
(experiment on graphing motion)
• Sonic
Ranger (activity on graphing motion)
• Walking
the Plank (activity)
Suggested Presentation
Begin by holding up the textbook and remarking on
its vast amount of information. A look at the table of contents shows there is
much to cover. Whereas some material will be covered in depth, some will not.
State that they will come to feel quite comfortable with an understanding of
much of the content, but not all. There isn’t time for a thorough treatment of
all material. So rather than bogging down at the beginning of your course and
ending up racing over material at the term’s end, you’re going to do it the
other way around, and race through this beginning chapter. Rather than tilling
this soil with a deep plow setting, you’re going to skim it and dig in later.
(This will help you avoid overtime on kinematics!)
Your first question: What means of motion has done
more to change the way cities are built than any other? [Answer: The elevator!]
Explain the importance of simplifying. Explain that
motion, for example, is best understood by first neglecting the effects of air
resistance, buoyancy, spin, and the shape of the moving object. Beneath these
factors are simple relationships that may otherwise be masked. So you’ll
concentrate on simple cases and avoid complexities. State that you’re not
trying to challenge them, but to teach them some of the physical science that
you yourself have learned. Better they understand a simple case than be miffed
by a complicated one that less clearly focuses on the main concept being
treated.
Aristotle’s Classification of Motion
Briefly discuss Aristotle’s views on motion. His
views were a good beginning for his time. They were flawed from the point of
view of what we know today, but his efforts to classify all things, motion
being one of them, was a boost in human thinking. Perhaps we remember him too
much for his errors, when in total, he did much to shape good thinking in his
time.
Galileo’s Concept of Inertia
Acknowledge the chief difference between Aristotle’s
approach and that of Galileo. The big difference between these two giant
intellects was the role of experiment—emphasized
by Galileo. The legendary experiment at the Leaning Tower of Pisa is a good
example. Interestingly, legend has it that many people who saw the falling
objects fall together continued to teach otherwise. Seeing is not always believing.
Ideas that are firmly established in one’s thinking are difficult to change.
People in science must be prepared to have their thinking challenged often.
Point to an object in the room and state that if it
started moving, one would reasonably look for a cause for its motion. We would
say that a force of some kind was responsible, and that would seem reasonable.
By force, you mean quite simply, a push or a pull. Tie this idea to the notion
of force maintaining motion as Aristotle saw it. State that a cannonball
remains at rest in the cannon until a force is applied, and that the force of
expanding gases drives the ball out of the barrel when it is fired. But what
keeps the cannonball moving when the gases no longer act on it? Galileo
wondered about the same question when a ball gained speed in rolling down an
incline but moved at constant speed on a level surface. This leads you into a
discussion of inertia. In the everyday sense, inertia refers to a habit or a
rut. In physics, it’s another word for laziness, or the resistance to change as
far as the state of motion of an object is concerned. Inertia was first
introduced not by Newton Newton
How much inertia an object has is related to the
amount of mass the object has. Mass is a measure of the amount of material in
an object. Weight is the gravitational attraction of the earth for this amount
of material. Whereas mass is basic, weight depends on location. You’d weigh a
lot more on Jupiter than on Earth, and a lot less on the surface of the moon.
Mass and weight are proportional; hence, they are often confused.
Mass is sometimes confused with volume. Comparing an
overstuffed fluffy pillow to a small automobile battery should convince anyone
that mass and volume are different. The unit of mass is the kilogram, and the
unit of volume is cubic meters or liters.
Density is a concept of fundamental importance and
is often confused with both mass and volume. Try the following demo to make the
concept of density clear. Measure the dimensions of a large wooden cube in
centimeters, and find its mass with a pan balance. Define density =
mass/volume. (Use the same cube when you discuss flotation later.) Some of your
students will unfortunately conceptualize density as massiveness or bulkiness
rather than massiveness per bulkiness, even when they give a verbal definition
properly. This can be helped with the following:
CHECK YOUR NEIGHBOR: Which has the greater density,
a cupful of water or a lake-full of water? A kilogram of lead or a kilogram of
feathers? A single uranium atom or the world?
I jokingly relate breaking a candy bar in two and
giving the smaller piece to my friend who looks disturbed. “I gave you the same
density of candy bar as I have.”
Contrast the density of matter and the density of
atomic nuclei that comprise so tiny a fraction of space within matter. From
about 2 g/cm3 to 2 ¥
1014 g/cm3. And in a further crushed
state, the interior of neutron stars, about 1016 gm/cm3.
Mass Versus Weight
To distinguish between mass and weight, compare the
efforts of pushing horizontally on a block of slippery ice on a frozen pond
versus lifting it. Or consider the weightlessness of a massive anvil in outer
space and how it would be difficult to shake. And if it were moving toward you,
it would be harmful to be in its way because of its great tendency to remain in
motion. The following demo (often used to illustrate impulse and momentum)
makes the distinction nicely:
DEMONSTRATION: Hang a massive ball by a string and
show that the top string breaks when the bottom is pulled with gradually more
force, but the bottom string breaks when the string is jerked. Ask which of
these cases illustrates weight. (Interestingly enough, it’s the weight of the
ball that makes for the greater tension in the top string.) Then ask which of
these cases illustrates inertia. (When jerked, the tendency of the ball to
resist the sudden downward acceleration, its inertia, is responsible for the
lower string breaking.) This is the best demo we know of for showing the
different effects of weight and mass.
One Kilogram Weighs 10 Newtons
Suspend a 1-kg mass from a spring scale and show
that it weighs 9.8 N. We round this off to 10 N, for precision is not needed at
this stage of learning.
Units of Force—Newtons
I suggest not making a big deal about the unfamiliar
unit of force—the newton. I simply
state that it is the unit of force used by physicists, and if students find
themselves uncomfortable with it, simply think of “pounds” in its place.
Relative magnitudes, rather than actual magnitudes, are the emphasis of
conceptual integrated science anyway. Do as my inspirational friend Burl Grey
does in Figure 2.10 and suspend a familiar mass from a spring scale. If the
mass is a kilogram and the scale is calibrated in newtons, it will read 9.8 N.
If the scale is calibrated in pounds, it will read 2.2 pounds. State that
you’re not going to waste valued time in unit conversions. (Students can do
enough of that in one of those dull physics courses they’ve heard about.) [I do
a short lesson on Unit Conversion in Screencast #10 that will save you
classtime.]
CHECK YOUR NEIGHBOR: Which has more mass, a 1-kg
stone or a 1-lb stone? [A 1-kg stone has more mass, for it weighs 2.2 lb. But
we’re not going to make a fuss about such conversions. If the unit newton bugs
you, think of it as a unit of force or weight in a foreign language for now!]
Net Force
Discuss the idea of more than one force acting on
something, and the resulting net force. Figure 2.9 captures the essence. Here’s
where you can introduce vectors. Note that the forces in the figure are
represented by arrows. Drawn to scale, these are vectors. Briefly distinguish between
vector quantities (like force, velocity, and, as we shall see, acceleration)
and scalar quantities (time, mass, volume).[Screencast #3 on Net Force is also
a time saver.]
Equilibrium for Objects at Rest
Cite other static
examples, where the net force is zero as evidenced by no changes in motion.
Hold the 1-kg mass at rest in your hand and ask how much net force acts on it.
Be sure they distinguish between the 9.8 N gravitational force on the object
and the zero net force on it—as
evidenced by its state of rest. (The concept of acceleration is introduced
shortly.) When suspended by the spring scale, point out that the scale is
pulling up on the object, with just as much force as the earth pulls down on
it. Pretend to step on a bathroom scale. Ask how much gravity is pulling on
you. This is evident by the scale reading. Then ask what the net force is that
acts on you. This is evident by your absence of any motion change. Consider two
scales, one foot on each, and ask how each scale would read. Then ask how the
scales would read if you shifted your weight more on one scale than the other.
Ask if there is a rule to guide the answers to these questions. There is: SF = 0 For any object in equilibrium, the net force
on it must be zero. Before answering, consider the skit outlined below.
Sign
Painter Skit Draw
on the board the sketch below, which shows two painters on a painting rig
suspended by two ropes. [Again, Screencast #1 covers this.]
Step 1: If both painters have
the same weight and each stands next to a rope, the supporting force in the
ropes will be equal. If spring scales were used, one on each rope, the forces
in the ropes would be evident. Ask what the scale readings in each rope would
be in this case. [The answer is that each rope will support the weight of one
man + half the weight of the rig—both scales will show equal readings.]
Step 2: Suppose one painter
walks toward the other as shown in the sketch, which you draw on the chalkboard
(or show via overhead projector). Will the reading in the left rope increase?
Will the reading in the right rope decrease? Grand question: Will the reading
in the left rope increase exactly as much as the decrease in tension in the
right rope? And if so, how does either rope “know” about the change in the
other rope? After neighbor discussion, be sure to emphasize that the answers to
these questions lie in the framework of the Equilibrium Rule: SF = 0.
Because there is no change in motion, the net force must be zero, which means
the upward support forces supplied by the ropes must add up to the downward
force of gravity on the two men and the rig. So a decrease in one rope must
necessarily be met with a corresponding increase in the other. (This example is
dear to my heart. Both Burl and I didn’t know the answer way back then—because neither he nor I had a model for
analyzing the problem. We didn’t know about Newton
The Support Force (Normal Force)
Ask what forces act on a book at rest on your
lecture table. Then discuss Figure 2.12, explaining that the atoms in the table
behave like tiny springs. This upward support force is equal and opposite to
the weight of the book, as evidenced by the book’s state of rest. The support force
is a very real force. Because it is always perpendicular to the surface, it is
called a normal force. Without it,
the book would be in a state of free fall.
Friction—A Force
That Affects Motion
Drag a block at constant velocity across your
lecture table. Acknowledge the force of friction, and how it must exactly
counter your pulling force. Show the pulling force with a spring balance. Now,
because the block moves without accelerating, ask for the magnitude of the
friction force. It must be equal and opposite to your scale reading. Then the
net force is zero. While sliding, the block is in dynamic equilibrium. That is,
SF = 0.
Equilibrium of Moving Things
If you’re in the car of a smoothly moving train and
you balance a deck of cards on a table, they are in equilibrium whether the
train is in motion or not. If there is no change in motion (acceleration), the
cards don’t “know the difference.”
Speed and Velocity
Define speed, writing its equation in longhand form
on the board while giving examples (automobile speedometers, etc.). Similarly
define velocity, citing how a race car driver is interested in his speed, whereas an airplane pilot is
interested in her velocity (speed and
direction). [More than enough information on kinematic definitions is in Screencast
#8.]
Motion Is Relative
Acknowledge that motion is relative to a frame of
reference. When walking down the aisle of a train at 1 m/s, your speed relative
to the floor of the train is different than your speed relative to the ground.
If the train is moving at 50 m/s, then your speed relative to the ground is 51
m/s if you’re walking forward, or 49 m/s if you’re walking toward the rear of
the train. Tell your class that you’re not going to make a big deal about
distinguishing between speed and velocity, but you are going to make a big deal
of distinguishing between speed or velocity and another concept—acceleration.
Galileo and Acceleration
Define acceleration, identifying it as a vector
quantity, and cite the importance of change.
That’s change in speed, or change in direction. Hence, both are acknowledged by
defining acceleration as a rate of change in velocity rather than speed. Ask
your students to identify the three controls in an automobile that enable the
auto to change its state of motion—that produce acceleration (accelerator, brakes, and steering wheel). State how
one lurches in a vehicle that is undergoing acceleration, especially for
circular motion, and state why the definition of velocity includes direction to
make the definition of acceleration all-encompassing. Talk of how without
lurching one cannot sense motion, giving examples of coin flipping in a
high-speed aircraft versus doing the same when the same aircraft is at rest on
the runway.
Units for Acceleration
Give numerical examples of acceleration in units of
kilometers/hour per second to establish the idea of acceleration. Be sure that
your students are working on the examples with you. For example, ask them to
find the acceleration of a car that goes from rest to 100 km/h in 10 seconds.
It is important that you not use examples involving seconds twice until they
taste success with the easier kilometers/hour per second examples. Have them
check their work with their neighbors as you go along. Only after they get the
hang of it, introduce meters/second/second in your examples to develop a sense
for the units m/s2. [Screencast #18 covers this].
Falling Objects
CHECK YOUR NEIGHBOR: If an object is dropped from an
initial position of rest from the top of a cliff, how fast will it be traveling at the end of 1 second? (You might add,
“Write the answer on your notepaper.” And then, “Look at your neighbor’s paper—if your neighbor doesn’t have the right
answer, reach over and help him or her—talk
about it.”)
After explaining the answer when class discussion
dies down, repeat the process, asking for the speed at the end of 2 seconds,
and then for 10 seconds. This leads you into stating the relationship v = gt,
which by now you can express in shorthand notation. After any questions,
discussion, and examples, state that you are going to pose a different question—not asking for how fast, but for how far.
Ask how far the object falls in 1 second.
Ask for a written response and then ask if the
students could explain to their neighbors why
the distance is only 5 m rather than 10 m. After they’ve discussed this for
almost a minute or so, ask, “If you maintain a speed of 60 km/h for 1 hour, how
far do you go?”—then, “If you
maintain a speed of 10 m/s for 1 second, how far do you go?” Important point: You’ll appreciably
improve your instruction if you allow some thinking time after you ask a
question. Not doing so is the folly of too many teachers. Then continue, “Then
why is the answer to the first question not 10 meters?” After a suitable time,
stress the idea of average velocity
and the relation d = vt. [Screencast #12 treats Free Fall.]
For accelerating objects that start from a rest
position, the average velocity is half the final velocity (average velocity =
[initial velocity + final velocity]/2).
CHECK YOUR NEIGHBOR: How far will a freely falling
object that is released from rest fall in 2 seconds? In 10 seconds? (When
your class is comfortable with this, then ask how far in 1/2 second.)
Investigate Figure 2.23 and have students complete
the speed readings. Ask what odometer readings (that measure distance) would be
for the speeds shown. To avoid information overload, we restrict all numerical
examples of free fall to cases that begin at rest. Why? Because it’s simpler
that way. (We prefer our students understand simple physics rather than be
confused about not-so-simple physics!) We do go this far with them:
Two-Track Demo
Look ahead at the two tracks shown in Exercise 79.
With your hand, hold both balls at the top end of the tracks and ask which will
get to the end first. Or you can quip, which will win the race, the slow one or
the fast one? Or, the one with the greatest average speed or the one with the
smaller average speed? Asked these latter ways, the question guides the answer.
But be ready to find that most students will intuitively know the balls will
reach the end with the same speed. (This is more obvious from a conservation of
momentum point of view.) But the question is not of speed, but of time—which gets there first. And that’s a
challenge to realize that! The speed gained by the ball on the lower part of
the dipped track is lost coming up the other side, so, yes, they reach the end
with the same speed. But the gained speed at the bottom of the dip means more
average speed overall. You’ll get a lot of discussion on this one. You can make
your own tracks quite simply. I got this idea from my friend and colleague,
Chelcie Liu, who simply bought a pair of equal length bookcase supports and
bent them by hand. They are more easily bent with the aid of a vice. [These
tracks make a concluding question in Screencast #31, when the conservation of
energy is discussed.]
Integrated Science—Biology,
Astronomy, Chemistry, and Earth Science: Friction Is Universal
To make the point that friction is indeed universal,
break students into small groups and ask them to list examples of friction that
relate to each of the major science subject areas—physics, chemistry, biology, earth science, and astronomy.
Have students state their examples so all can appreciate the diversity of
friction applications. Also, you might have a brick available to students
interested in verifying the concept discussed in the Concept Check question for
themselves.
Integrated Science—Biology:
Hang Time
This fascinating idea completes the chapter. Most
students (and other instructors) are amazed that the best athletes cannot
remain airborne for a second in a standing jump. This prompts great class
discussion. You can challenge your students by saying you’ll award an A to any student who can do a 1-second
standing jump! You’ll have takers; but you’ll award no A’s for this feat.
No comments:
Post a Comment