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Dec 2011

Volume 49, Issue 9, pp. 532-590

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Optical transform for the explanation of DNA Photo 51

Volker Krasemann

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 532

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01.50.My Demonstration experiments and apparatus
87.14.gk DNA
87.15.B- Structure of biomolecules
01.40.ek Secondary school

The shoulders of giants: An appreciation

David S. Martin

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 532

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01.40.ek Secondary school

A final idea

Samuel Derman

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 533 | Cited 1 time

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01.40.gb Teaching methods and strategies

Do the equations of physics encapsulate cause and effect?

Kenneth W. Ford

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 533

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01.50.Kw Techniques of testing
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ON A HIGH PITCH

Paul Hewitt

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 534

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99.10.-x Errata and other corrections
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
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Inexpensive Data Acquisition with a Sound Card

Umer Hassan, Saad Pervaiz, and Muhammad Sabieh Anwar

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 537 | Cited 2 times

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Signal generators, oscilloscopes, and data acquisition (DAQ) systems are standard components of the modern experimental physics laboratory. The sound card, a built-in component in the ubiquitous personal computer, can be utilized for all three of these tasks1,2 and offers an attractive option for labs in developing countries such as ours—Pakistan—where affordability is always of prime concern. In this paper, we describe in a recipe fashion how the sound card is used for DAQ and signal generation.
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01.50.My Demonstration experiments and apparatus
01.50.Pa Laboratory experiments and apparatus
01.50.ht Instructional computer use
01.50.Lc Laboratory computer use

About the International System of Units (SI) Part II. Organization and General Principles

Gordon J. Aubrecht, II, Anthony P. French, and Mario Iona

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 540

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As all physicists know, all units are arbitrary. The numbering system is anthropocentric; for example, the Celsius scale of temperature has 100 degrees between the boiling point of water at STP and the freezing point of water. The number 100 is chosen because human beings have 10 fingers. The best units might be based on physical constants, for example, defining temperature in terms of absolute zero and the triple point of water, which are presumably the same everywhere in the universe. Even these units are anthropocentric, though, because, for example, why should water be more fundamental than another material? (Answer: only because we live on Earth, where the abundance of liquid water has made our lives possible.) The basic SI units (base units, see Sec. 2) are as arbitrary as any other set.
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01.50.-i Educational aids
06.20.fa Units
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Black Holes and the Large Hadron Collider

Arunava Roy

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 544

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The European Center for Nuclear Research or CERN's Large Hadron Collider (LHC) has caught our attention partly due to the film “Angels and Demons.” In the movie, an antimatter bomb attack on the Vatican is foiled by the protagonist. Perhaps just as controversial is the formation of mini black holes (BHs). Recently, the American Physical Society1 website featured an article on BH formation at the LHC.2 This article examines some aspects of mini BHs and explores the possibility of their detection at the LHC.
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01.50.-i Educational aids
04.70.-s Physics of black holes
29.40.Gx Tracking and position-sensitive detectors

Revealing the Hidden Wave: Using the Very Small Radio Telescope to Teach High School Physics

Michael Doherty, Vincent L. Fish, and Madeleine Needles

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 546

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Scientists and teachers have worked together to produce teaching materials for the Very Small Radio Telescope (VSRT), an easy-to-use, low-cost apparatus that can be used in multiple laboratory experiments in high school and university physics and astronomy classes. In this article, we describe the motivation for the VSRT and several of the laboratory investigations that are being used in local high schools.
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01.50.Pa Laboratory experiments and apparatus
95.55.Jz Radio telescopes and instrumentation; heterodyne receivers

Why Do Objects Cool More Rapidly in Water Than in Still Air?

Craig F. Bohren

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 550 | Cited 2 times

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An Internet search for why objects, especially humans, cool more rapidly in water than in air, both at the same temperature, and by how much, yields off-the-cuff answers unsupported by experiment or analysis. To answer these questions in depth requires a smattering of engineering heat transfer, including radiative transfer, and the different thermophysical properties of the two fluids. The correct ratio for humans is closer to 2 than to 10, and if this were not so, swimming in cool water could be fatal.
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01.50.-i Educational aids
47.27.te Turbulent convective heat transfer

Additional Crime Scenes for Projectile Motion Unit

Dan Fullerton and David Bonner

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 554

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Building students' ability to transfer physics fundamentals to real-world applications establishes a deeper understanding of underlying concepts while enhancing student interest. Forensic science offers a great opportunity for students to apply physics to highly engaging, real-world contexts.1 Integrating these opportunities into inquiry-based problem solving in a team environment provides a terrific backdrop for fostering communication, analysis, and critical thinking skills. One such activity, inspired jointly by the museum exhibit “CSI: The Experience”2 and David Bonner's TPT article “Increasing Student Engagement and Enthusiasm: A Projectile Motion Crime Scene,”3 provides students with three different crime scenes, each requiring an analysis of projectile motion. In this lesson students socially engage in higher-order analysis of two-dimensional projectile motion problems by collecting information from 3-D scale models and collaborating with one another on its interpretation, in addition to diagramming and mathematical analysis typical to problem solving in physics.
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01.50.-i Educational aids
45.40.Gj Ballistics (projectiles; rockets)
89.20.Mn Forensic science

Captain R. Rubber Ducky: A STEM- Driven Project in Aquatic Robotics

Muntaha Sheikh, Mark Fulbright, and George Hademenos

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 557

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Project-based learning is a research-based instructional tool that has proven to be effective in all secondary curricular disciplines, particularly in the areas of science, technology, engineering, and mathematics (STEM).1–5 A project is an applied activity, often hands-on, where the students are challenged to successfully address a problem. In many STEM projects, the problem is solved by designing, constructing, and operating a device to accomplish tasks inherent to the solution of the problem. Project-based learning exemplifies the core values of the scientific process, including peer discussion and collaboration, problem-solving skills, modeling, testing, data analysis, and forming conclusions.
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01.50.My Demonstration experiments and apparatus
01.50.-i Educational aids

AAPT/PTRA — A Part of the Solution

George Amann, Jan Mader, Karen Jo Matsler, and Jim Nelson

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 560 | Cited 2 times

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A train barrels directly toward a stone wall. It looks like a disaster is inevitable. Suddenly, a group of railroad workers run to a switch that changes the direction of the train. They reroute the train onto a new track by throwing the switch just in time. Perhaps you had not known what to do, nor were you strong enough to do it yourself, but you now see that it was not a forgone conclusion that the train had to run into the wall. In this scenario, the train represents precollege physics education in the United States. The wall represents the classroom situation that many teachers find when they are assigned to teach physics. These teachers often find themselves teaching a subject for which they were not adequately prepared. It is not their fault, but rather the result of the necessity of having a teacher assigned to the class. The United States needs students to be prepared for a future in which science and technology will be more and more a part of everyone's life, and there are not enough well-prepared physics teachers graduating from colleges and universities. So the train is headed toward the wall. “Who are the strong railroad workers?” you ask. These are the 200 Physics Teaching Resource Agents (PTRAs), who for the past 25 years have been selected and trained by AAPT to do workshops for practicing physics and physical science teachers. Thus AAPT celebrated the PTRA silver anniversary during the 2010 AAPT meeting in Portland.1 And APS recognized this achievement with their 2011 Excellence in Physics Education Award.2
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01.40.J- Teacher training
01.50.-i Educational aids
01.40.gb Teaching methods and strategies

Leadership in Freshman Physics

Carina M. Rebello, Deborah Hanuscin, and Somnath Sinha

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 564

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Physics First—a movement to invert the traditional science course sequence to teach physics at the ninth-grade level—is gaining interest. However, there is limited literature exploring how to support teachers in successfully implementing Physics First. To address this, a professional development (PD) program supporting a cadre of teacher-leaders was developed. Its impetus is to facilitate teacher-leaders in becoming advocates for excellence through developing their physics content knowledge and use of research-based pedagogy. The primary aim of this paper is to illustrate how Leadership in Freshman Physics, an NSF Math and Science Partnership (MSP), designed a leadership component to support high school physics teacher-leaders in a district-wide implementation of the Physics First curriculum. We describe lessons learned from our implementation and provide suggestions for future PD programs emphasizing teacher-leadership.
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01.40.J- Teacher training
01.50.-i Educational aids
01.40.ek Secondary school

The Static Ladder Problem with Two Sources of Friction

Jonathan Bennett and Alex Mauney

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 567 | Cited 1 time

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The problem of a ladder leaning against a wall in static equilibrium is a classic example encountered in introductory mechanics texts.1 Most discussions of this problem assume that the static frictional force between the ladder and wall can be ignored. A few authors2,3 consider the case where the static friction coefficients between ladder/wall (μs,wall) and ladder/floor (μs,floor) are equal. This situation is indeterminate (i.e. without modeling the elasticity of the ladder, it is not possible to solve for all the external forces), but the critical angle beyond which the ladder will not remain in equilibrium can nevertheless be determined if the ladder is assumed to be perfectly rigid. The case where μs,wall ≠ μs,floor has also been considered by several authors.4–6 Assuming a perfectly rigid ladder, we will show that the critical angle in this case can be determined through an interesting application of the inequality describing the magnitude of the static friction force. We will also show how it is possible to experimentally investigate the critical angle in this situation using commonly available lab equipment.
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01.50.-i Educational aids
46.55.+d Tribology and mechanical contacts

Jogging on a Carousel

Alpha E. Wilson

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 570

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To jog around the periphery of a carousel at rest requires that the jogger experience a constant state of acceleration perpendicular to the direction of motion and directed toward the axis of rotation (centripetal). The jogger could achieve this centripetal acceleration by leaning inward, thereby using a horizontal weight component to provide the necessary centripetal force. There are two ordinary cases of circular motion involving the carousel that can be handled by the simple centripetal acceleration formula, where the joggers speed v is squared and then divided by the radius r of the path being followed (a = v2/r). One case would be as above, with the carousel at rest and the jogger moving on a circular path around it. The other case would be the jogger at rest on the carousel at a radial point r while it is moving with linear speed v. The situation can be made significantly more interesting and informative by letting the jogger be in motion while the carousel is in motion.
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01.50.-i Educational aids
87.85.G- Biomechanics
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Non-Mathematical Explanation of Precession

John Cordell

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 572

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The phenomenon of precession is necessary to explain the motion of footballs, gyroscopes, tops, the Earth, and many other interesting physical systems, but it was very hard for me to understand as a student and is very difficult to teach to students now. Many explanations of precession in physics textbooks are highly mathematical and hard to understand conceptually. This puts the topic of precession out of reach for many introductory physics students. I hope that this explanation of precession will help teachers and students to understand the phenomenon on a more conceptual level.
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01.50.-i Educational aids
45.20.dc Rotational dynamics
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Laboratory Activity: Specific Heat by Change in Internal Energy of Silly Putty

John Koser

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 574

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Students in introductory physics courses often don't study thermodynamics or thermodynamic events. If any thermal physics is taught in introductory courses (e.g., Physics 101 for Liberal Arts Majors), it usually involves the concepts of specific heat and various temperature scales. Seldom are the first and second laws of thermodynamics taught in detail. In this article, we look at a means to obtain real-time data that will lead to clarifying the first law.
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01.50.Pa Laboratory experiments and apparatus
05.70.Ce Thermodynamic functions and equations of state

Figuring the Acceleration of the Simple Pendulum

Martin Lieberherr

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 576

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The centripetal acceleration has been known since Huygens' (1659) and Newton's (1684) time.1,2 The physics to calculate the acceleration of a simple pendulum has been around for more than 300 years, and a fairly complete treatise has been given by C. Schwarz in this journal.3 But sentences like “the acceleration is always directed towards the equilibrium position” beside the picture of a swing on a circular arc can still be found in textbooks, as e.g. in Ref. 4. Vectors have been invented by Grassmann (1844)5 and are conveniently used to describe the acceleration in curved orbits, but acceleration is more often treated as a scalar with or without sign, as the words acceleration/deceleration suggest. The component tangential to the orbit is enough to deduce the period of the simple pendulum, but it is not enough to discuss the forces on the pendulum, as has been pointed out by Santos-Benito and A. Gras-Marti.6 A suitable way to address this problem is a nice figure with a catch for classroom discussions or homework. When I plotted the acceleration vectors of the simple pendulum in their proper positions, pictures as in Fig. 1 appeared on the screen. The endpoints of the acceleration vectors, if properly scaled, seemed to lie on a curve with a familiar shape: a cardioid. Is this true or just an illusion?
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01.50.-i Educational aids
07.10.-h Mechanical instruments and equipment
45.05.+x General theory of classical mechanics of discrete systems

Rearview Mirror Dimming Function

William Layton

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 578

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Students are often unaware of the little tab on a rear-view mirror that is used to dim headlights from the rear. Those who know about this tab are usually interested in knowing how it works. Explanations of the optics involved can be found in Serway and Jewett1 and Jones and Edge.2 An alternate explanation is given below:
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01.50.My Demonstration experiments and apparatus
42.79.Bh Lenses, prisms and mirrors

A Simple Tool for Integration and Differentiation of Tabular Values in Microsoft Excel

Ole Anton Haugland

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 580

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There are many software alternatives for analyzing experimental data in our physics teaching. I prefer to use Excel® because of its flexibility and widespread use elsewhere in our society. Whatever our students will work with in their future career, they almost certainly will have access to a spreadsheet. For a long time I have missed a tool for integrating and differentiating tabular values in Excel. For every new version I thought it would appear, but it did not. Such a tool could also be useful if you analyze data from other sources than your own experiment, for example, data from the Internet. Therefore, I have written a simple tool that can be integrated seamlessly into Excel as an add-in. It is written in Excels powerful macro language Microsoft Visual Basic for Applications. The tool can be downloaded online1 and there are two versions of it: one for Excel 2003 and one for Excel 2007/2010.
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01.50.-i Educational aids
01.30.Kj Handbooks, dictionaries, tables, and data compilations
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Quizzes that foster and motivate learning

Boon Leong Lan

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 581

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Abstract Unavailable
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01.50.-i Educational aids
01.40.-d Education

Photo of the Month: Frozen in time

Don Easton

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 582

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01.50.-i Educational aids
01.40.-d Education
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Being sensational

Diane Riendeau, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 583

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01.50.My Demonstration experiments and apparatus
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Grading without losing all your time (and your mind!)

Kathleen A. Harper

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 584 | Cited 1 time

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One aspect of teaching that most new teachers tend to grossly underestimate is the amount of time that will be spent grading. At least that is my impression, based upon my own experience and that of my friends. Additionally, it can sometimes be difficult to develop grading schemes for particular assignments, and too often this realization happens when one sits down to grade the assignment in question.
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01.50.-i Educational aids
01.40.J- Teacher training
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Fermi Questions

Larry Weinstein, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 586

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01.50.-i Educational aids
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High School Physics Offerings by Socioeconomic Profile

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 586

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This fall we have been examining physics classes in U.S. high schools by the principal's assessment of the socioeconomic profile of each school.1 This month we turn our focus to the distribution of high school physics enrollment across the different types of physics offered. Not only do fewer students take physics at “worse off” schools (see the October issue), but the types of physics courses students take also differs by socioeconomic profile. About 10% of the students taking physics at “worse off” schools take AP and second-year physics; almost 20% of the students at “better off” schools take these courses. At “worse off” schools, a higher proportion of students are enrolled in conceptual courses, including Physics First and regular physics taught using a conceptual textbook. The data we have presented over the last four months suggests that differences in physics taking in high school by blacks and Hispanics are driven, in part, by underlying socioeconomic factors. Other factors, such as the availability of additional seats in physics classes and the ability of teachers to attract students to physics, also impact physics taking. It is unlikely that the racial and ethnic differences in physics taking in high school will decrease unless the underlying factors are addressed.
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99.10.-x Errata and other corrections
01.40.Di Course design and evaluation
01.40.ek Secondary school
01.75.+m Science and society
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A bar bouncer

Boris Korsunsky, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 587

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Abstract Unavailable
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01.50.Pa Laboratory experiments and apparatus
46.55.+d Tribology and mechanical contacts
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The vibrations in a rubber baseball bat

David Kagan

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 588 | Cited 1 time

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01.50.My Demonstration experiments and apparatus
46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
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Bob Beichner a winner of 2011 McGraw Prize in Education for NCSU SCALE-UP Physics Program; five-minute video at tinyurl.com/beichner

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 589

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01.50.-i Educational aids
01.40.-d Education

Vernier's Video Physics App on iPad 2; www.youtube.com/watch?v=pPKRBqskC3M

Thomas Kenyon, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 589

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01.50.ff Films; electronic video devices
01.50.Lc Laboratory computer use
45.40.Gj Ballistics (projectiles; rockets)

IR Cameras and the Baseball World Series; tinyurl.com/nathanIR

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 589

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01.50.-i Educational aids
01.55.+b General physics
42.79.Pw Imaging detectors and sensors
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From Jars to the Stars: How Ball Came to Build a Comet-Hunting Machine,: Todd Neff

Albert A. Bartlett

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 590

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Abstract Unavailable
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01.30.Vv Book reviews
01.50.-i Educational aids
96.25.Fx Atmospheres
96.30.Cw Comets

MicroReviews by the Book Review Editor: Visions of the Multiverse: Do Parallel Realities Exist?/Is Our Universe One of Many?: Steven Manly

John L. Hubisz, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 590

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Abstract Unavailable
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01.50.-i Educational aids
98.80.-k Cosmology
01.30.Vv Book reviews

MicroReviews by the Book Review Editor: The Scientific Endeavor: A Primer on Scientific Principles and Practice,: Jeffrey A. Lee

John L. Hubisz, Column Editor

The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 590

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01.50.-i Educational aids
01.30.Vv Book reviews
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