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Feb 2011

Volume 49, Issue 2, pp. 68-128

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Meet Your New President, David Sokoloff

Priscilla Laws

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 68

Online Publication Date: Jan 2011

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01.50.-i Educational aids
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“It's Your AAPT!”

David R. Sokoloff, AAPT President

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 69

Online Publication Date: Jan 2011

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99.10.Np Editorial note
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WHOPPED CAN

Paul Hewitt

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 70

Online Publication Date: Jan 2011

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01.50.F- Audio and visual aids
01.50.fh Posters, cartoons, art, etc.
01.50.My Demonstration experiments and apparatus
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Unfortunate Outcomes of a “Funny” Physics Problem: Some Eye‐Opening YouTube Comments

Josip Slisko and Dewey Dykstra, Jr.

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 72

Online Publication Date: Jan 2011

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The impressions we make as instructors of physics can affect student learning and public perception of physics teachers, physics as an academic subject, and physics as a profession. There are many sources from which we can collect evidence of these impressions. Among these sources are online public forums such as those at the Internet site known as YouTube. Whether we are proud of these impressions we make or not, we should consider how constructive these impressions are for our students' physics learning and their impact on the public perception of physics and the community of physicists.
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01.50.-i Educational aids
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Standing Waves in a Nonuniform Medium

Paul Gluck

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 76 | Cited 1 time

Online Publication Date: Jan 2011

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A recent note in this journal1 presented a demonstration of standing waves along a cord consisting of two parts having different material densities, showing different sized wavelengths in each part. A generalization of that experiment to a continuously varying linear mass density is to vibrate a strip of material with gradually varying width (mass per unit length), in order to show that as the strip gets wider, the wavelength becomes shorter. Figure 1 shows the setup. It consists of a mechanical driver fed by a signal generator, and a strip of flexible fabric connected at its narrow end to the driver, nailed to a suitable piece of wood at the wider end. The strip is in the shape of a trapeze, 2 cm and 10 cm at its ends and some 50 cm long in its middle. It may be cut from the inner tube of a tire, or from body‐building elastic strips.
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01.50.My Demonstration experiments and apparatus
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Siphons, Revisited

Alex Richert and P. ‐M. Binder

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 78

Online Publication Date: Jan 2011

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The siphon is a very useful example of early technology, the operation of which has long been well understood. A recent article1 makes the claim that established beliefs regarding this device are incorrect and proposes a “chain model” in which intermolecular forces within the fluid play a large role while atmospheric pressure does not. We have carefully tested, and disproved, this claim using four simple experiments employing inexpensive, easily available apparatus. We complement the experiments with a discussion of conceptual issues related to the device and by invoking earlier studies and observations.2–8 Our findings fully support an explanation based on Bernoulli's equation in which both gravity and pressure play important roles, but intermolecular forces do not.
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01.50.My Demonstration experiments and apparatus

The Internal Ballistics of an Air Gun

Mark Denny

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 81 | Cited 1 time

Online Publication Date: Jan 2011

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The internal ballistics of a firearm or artillery piece considers the pellet, bullet, or shell motion while it is still inside the barrel. In general, deriving the muzzle speed of a gunpowder firearm from first principles is difficult because powder combustion is fast and it very rapidly raises the temperature of gas (generated by gunpowder deflagration, or burning), which greatly complicates the analysis. A simple case is provided by air guns, for which we can make reasonable approximations that permit a derivation of muzzle speed. It is perhaps surprising that muzzle speed depends upon barrel length (artillerymen debated this dependence for centuries, until it was established experimentally and, later, theoretically1). Here we see that a simple physical analysis, accessible to high school or freshmen undergraduate physics students, not only derives realistic muzzle speed but also shows how it depends upon barrel length.
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01.50.Kw Techniques of testing
45.40.Gj Ballistics (projectiles; rockets)

Screencasts for Physics Students

Mark Vondracek

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 84

Online Publication Date: Jan 2011

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This paper outlines the use of “how to” videos, in the form of a screencast using a tablet computer, and posting the videos online. These videos are useful for when students miss a class, for those students who need to review a lesson or examples used in class when doing homework or reviewing for a test, for instructors of online classes, and also for instructors if they have to miss a day of class. Students overwhelmingly report this to be a useful and effective tool that has allowed them to catch up more easily after missing one or more days of class and for reviewing material from class.
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01.50.ff Films; electronic video devices
01.50.My Demonstration experiments and apparatus
01.40.gb Teaching methods and strategies

“Staying in Focus” — An Online Optics Tutorial on the Eye

Barbara M. Hoeling

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 86 | Cited 1 time

Online Publication Date: Jan 2011

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The human eye and its vision problems are often used as an entry subject and attention grabber in the teaching of geometrical optics.1 While this is a real‐life application students can relate to, it is difficult to visualize how the eye forms images by studying the still pictures and drawings in a textbook. How to draw a principal ray diagram or how to calculate the image distance from a given object distance and focal length might be clear to most students after studying the book, but even then they often lack an understanding of the “big picture.” Where is the image of a very far away object located? How come we can see both far away and close‐by objects focused (although not simultaneously)? Computer animations,2 popular with our computer‐game savvy students, provide considerably more information than the still images, especially if they allow the user to manipulate parameters and to observe the outcome of a “virtual” experiment. However, as stand‐alone learning tools, they often don't provide the students with the necessary physics background or instruction on how to use them.
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01.50.ht Instructional computer use
42.15.-i Geometrical optics

When Does Air Resistance Become Significant in Free Fall?

Pirooz Mohazzabi

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 89

Online Publication Date: Jan 2011

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In introductory physics laboratories, students who experiment with freely falling objects frequently attribute any error in their experimental results to the presence of air resistance. It is, therefore, important to realize when and at what point during a free fall air resistance begins to play a significant role in the motion of the falling object. In this paper we address this question, and we show that blaming air resistance for errors in free‐fall experiments in introductory physics laboratories is almost never justified.
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01.50.-i Educational aids
45.40.-f Dynamics and kinematics of rigid bodies
45.50.-j Dynamics and kinematics of a particle and a system of particles

Physics Takes Priority in Teaching Assignments

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 90

Online Publication Date: Jan 2011

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During the 2008–09 academic year, 27,000 high school teachers taught physics in U.S. high schools. Some of these teachers taught only one physics class, but, for the first time in our survey history, over half taught all physics or mostly physics. While the proportion teaching physics classes exclusively did not change from 2005, those teaching most of their classes in physics grew. This suggests a shrinking “hidden” capacity to teach more physics classes. This “hidden” capacity refers to the additional physics classes that a physics teacher who does not teach physics exclusively could teach. As more teachers teach a majority of their classes in physics, this could increase their enthusiasm for physics. The increased enthusiasm could spur even more interest in physics among students and faster growth in physics taking.
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01.50.-i Educational aids
01.40.ek Secondary school
01.40.G- Curricula and evaluation

Whither Does the Sun Rove?

Alejandro Gangui

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 91

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If one asked some friends where on the horizon they should expect to see the sunrise, half of the answers would be 舠in the east.舡 Of course, something analogous would happen with the sunset and the west. However, sunrise and sunset virtually never occur at these cardinal points. In fact, those answers correctly describe observations only during the equinoxes, when either autumn or spring begin. Once we recall this, the next natural question to ask ourselves is: how far from the east (or from the west) the rising (or setting) Sun is located for a given latitude of the observer and for a given day of the year. In this paper we supply some simple tools to easily visualize the angular (southward or northward) departure of the rising and setting Sun on the horizon from the east-west direction in a pictorial way, without the need of mathematics. These tools have proven a valuable resource in teaching introductory physics and astronomy courses.
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01.50.-i Educational aids
96.60.-j Solar physics
01.40.Ha Learning theory and science teaching

Teaching Scientific Inquiry with Galaxy Zoo

Stephanie J. Slater, Timothy F. Slater, and Daniel J. Lyons

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 94

Online Publication Date: Jan 2011

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The universe of topics to choose from when teaching an astronomy course is astronomically immense. This wide array of opportunity presents some inherently difficult choices for teachers at all levels on how to limit the scope of the course to make the syllabus manageable. As but one example, consider that even the most experienced astronomy teacher must choose between focusing on the astrophysics of stellar processes or on the nomenclature for stars and constellations because there is rarely time to give both justice. One might go as far as saying that planning an astronomy course is similar to the perspective offered by Michael Pollan in his book The Omnivore's Dilemma, which can be paraphrased as, “When entering a modern grocery store in the U.S. with unlimited choices, what is it that one chooses to eat and why?” Indeed, teaching about the entire universe in a single astronomy course involves some serious choices, as one can most certainly not teach everything.
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01.50.-i Educational aids
01.40.-d Education
98.35.-a Characteristics and properties of the Milky Way galaxy

Physics in the News: The Deepwater Horizon Disaster

Albert A. Bartlett

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 97

Online Publication Date: Jan 2011

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On April 20, 2010, there were explosions and fire on the drilling “ship” the Deepwater Horizon, which was drilling for petroleum in the Gulf of Mexico about 70 kilometers south of the Louisiana coast. The spectacular fires ultimately caused the Deepwater Horizon to sink on April 22. There were 126 people on the ship before the fire. After the sinking, 11 people were missing and presumed dead. After the ship sank, several hundred cubic meters of petroleum began to emerge each day from the broken underwater piping on the sea floor. The petroleum rose to the surface, where the winds caused it to drift toward the shores of the Gulf. The oil slick is a great threat to the coastal ecosystems. “President Obama…called the scene unfolding in the Gulf a ‘massive and potentially unprecedented environmental disaster.’”1 Not only is this an environmental disaster, it is a big setback for deepwater drilling for petroleum and for our nation's efforts to reduce our dependence on foreign oil.
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01.50.-i Educational aids
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics

The Hope of Audacity® (To Teach Acoustics)

Jennifer Groppe

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 99

Online Publication Date: Jan 2011

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When working on an oral history project, my brother recommended that I download a free audio recording and editing program called Audacity®. I have since discovered that it is a fantastic tool for students to visualize sound waves and to understand the meaning of amplitude, frequency, and superposition. This paper describes a collection of demonstrations, most of which require only a computer, a set of speakers, and a projector.
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01.50.fd Audio devices
43.00.00 Acoustics

Dramatic (and Simple!) Demonstration of Newton's Third Law

Gerald Feldman

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 103 | Cited 1 time

Online Publication Date: Jan 2011

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An operational understanding of Newton's third law is often elusive for students. Typical examples of this concept are given for contact forces that are closer to the students' everyday experience. While this is a good thing in general, the reaction force can sometimes be taken for granted, and the students can miss the opportunity to really think about what is going on. In the case of magnetic forces, however, the notion of action at a distance actually requires a careful inspection of the forces involved and thereby promotes a more detailed analysis of the situation. In this paper, a simple demonstration of Newton's third law is presented in the context of a magnet falling through a hollow conducting tube. The results are unambiguous and lead the students to an irrefutable verification of Newton's third law.
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01.50.My Demonstration experiments and apparatus
45.20.D- Newtonian mechanics

Effective Torsion and Spring Constants in a Hybrid Translational‐Rotational Oscillator

Zein Nakhoda and Ken Taylor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 106

Online Publication Date: Jan 2011

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A torsion oscillator is a vibrating system that experiences a restoring torque given by τ = −κθ when it experiences a rotational displacement θ from its equilibrium position. The torsion constant κ (kappa) is analogous to the spring constant k for the traditional translational oscillator (for which the restoring force F is proportional to the linear displacement x of the mass). An effective torsion oscillator can be constructed by integrating a spring's translational harmonic properties into an Atwood2 arrangement where a disk serves as the pulley for the system and the spring(s) exert restoring torques on the oscillating disk. Both effective torsion constants and effective spring constants can be expressed in terms of adjustable parameters of the system. These expressions enable one to theoretically describe the motion of the hybrid oscillator and to calculate its period. A comparison of the translational and rotational interpretations teaches of their analogous mathematical properties and challenges the intuitive skills of those considering such systems.
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45.20.dc Rotational dynamics
45.20.da Forces and torques

Physics in a Glitter Ball

Walter Trikosko

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 110

Online Publication Date: Jan 2011

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Maui Toys' Water Bouncer (Fig. 1) is a water‐filled ball containing glitter. Buy one and put it on your desk and students can't keep their hands off of it. Pitch the ball in the air giving it a quick spin. When you catch it you will see a sparkling vortex. Twist the ball around different ways and the angular momentum of the fluid keeps the axis of the glitter vortex fixed in one direction.
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01.50.-i Educational aids
42.25.Gy Edge and boundary effects; reflection and refraction

Determining Planetary Temperatures with the Stefan‐Boltzmann Law

Michael C. LoPresto and Nichole Hagoort

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 113

Online Publication Date: Jan 2011

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What follows is a description of several activities involving the Stefan‐Boltzmann radiation law that can provide laboratory experience beyond what is normally found in traditional introductory thermodynamics experiments on thermal expansion, specific heat, and heats of transformation. The activities also provide more extensive coverage of and hands‐on experience with the radiation law than is normally found in a traditional thermodynamics curriculum.
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01.50.My Demonstration experiments and apparatus
01.40.gb Teaching methods and strategies
96.12.Jt Atmospheres
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Simple apparatus for the measurement of mechanical properties of solids

Ligia R. Gomes, Ana Amado, Manuel C. Torres, and Luís M. N. B. F. Santos

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 117

Online Publication Date: Jan 2011

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This paper describes a simple apparatus we have developed for determining elastic properties of materials. The easily constructed system may be used to measure the elongation or compression of a sample to which a succession of loads is applied. This allows stress‐strain curves to be plotted and analyzed. We describe the construction and use of the apparatus and present some sample data.
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01.50.Pa Laboratory experiments and apparatus
06.60.-c Laboratory procedures
46.25.-y Static elasticity
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Teaching F = ma using a flying saucer toy

Yasuo Ogawara

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 119

Online Publication Date: Jan 2011

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For beginning students it is often difficult to understand Newton's second law.1,2 I wrote the following question for a mid‐term examination.
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01.50.Wg Physics of toys
01.40.gf Theory of testing and techniques
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Consider Your Audience

Diane Riendeau, Column Editor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 120

Online Publication Date: Jan 2011

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Special thanks to my students: Sam Solovy, Dan Coltun, Peter Kerschke, Matan Farhi, Tara Hanusa, Eric Silcroft, David Goldman and Mike Spinello for their favorite videos.
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01.50.ht Instructional computer use
01.40.gb Teaching methods and strategies
01.50.Kw Techniques of testing
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“Retests”: A better method of test corrections

Jeff McManus

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 121

Online Publication Date: Jan 2011

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Physics instructors at all levels employ a variety of techniques to encourage students to reflect on and correct mistakes made on quizzes, unit tests, or exams. A thorough analysis of several methods was recently published in these pages that compared several variations of quiz corrections in college courses.1 One common method is to have students rewrite the solutions to the questions or problems that they missed, with the goal of earning some part of the missed points. While this method is helpful for some students, it often discourages students with already decent grades to reflect on their work. I use a method called “retesting” with my AP® Physics C students that I learned from my high school geometry teacher, Bill Kramer. I feel his clever method offers significant advantages over more traditional approaches.
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01.50.-i Educational aids
01.40.-d Education
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Fermi Questions

Larry Weinstein, Column Editor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 122

Online Publication Date: Jan 2011

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01.50.-i Educational aids
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Hanging by a Thread

Boris Korsunsky, Column Editor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 123

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.-i Educational aids
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Using a laptop screen to model point‐source, line‐source, and planar‐source fields

Peter H. Bohacek and Rebecca Gobel

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 124

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.ht Instructional computer use
01.40.-d Education
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The Engineer Guy/ by Bill Hammock of University of Illinois at Urbana‐Champaign

Kevin O'Donnell

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 127

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.ht Instructional computer use
01.40.gf Theory of testing and techniques

Mathematical Doodling and mathematical food cutting, balloon twisting, paper musical instruments, music organs, etc. by Vi Hart

Andromeda MacIsaac

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 127

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.ff Films; electronic video devices

PBS Circus Physics

Dwight Souder

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 127

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.F- Audio and visual aids
46.70.-p Application of continuum mechanics to structures
45.20.df Momentum conservation
45.40.Gj Ballistics (projectiles; rockets)

Trolling the physics teaching blogs:

Frank Noschese and Dan Fullerton

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 127

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.50.ht Instructional computer use
01.40.gb Teaching methods and strategies
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Physics for Future Presidents: The Science Behind the Headlines and Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know: Richard A. Muller

John L. Hubisz, Column Editor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 128

Online Publication Date: Jan 2011

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Abstract Unavailable
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01.30.Vv Book reviews

Questioning Einstein: Is Relativity Necessary?: Tom Bethell

John L. Hubisz, Column Editor

The Physics Teacher -- February 2011 -- Volume 49, Issue 2, pp. 128

Online Publication Date: Jan 2011

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01.30.Vv Book reviews
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