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Apr 2011

Volume 49, Issue 4, pp. 196-256

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Teaching Newton's Laws with the iPod Touch in Conceptual Physics

Angela M. Kelly

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 202 | Cited 1 time

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One of the greatest challenges in teaching physics is helping students achieve a conceptual understanding of Newton's laws. I find that students fresh from middle school can sometimes recite the laws verbatim (“An object in motion stays in motion…” and “For every action…”), but they rarely demonstrate a working knowledge of how to apply them to observable phenomena. As a firm believer in inquiry‐based teaching methods, I like to develop activities where students can experiment and construct understandings based on relevant personal experiences. Consequently, I am always looking for exciting new technologies that can readily demonstrate how physics affects everyday things. In a conceptual physics class designed for ninth‐graders, I created a structured activity where students applied Newton's laws to a series of free applications downloaded on iPod Touches. The laws had been introduced during the prior class session with textual descriptions and graphical representations. The course is offered as part of the Enlace Latino Collegiate Society, a weekend enrichment program for middle and high school students in the Bronx. The majority of students had limited or no prior exposure to physics concepts, and many attended high schools where physics was not offered at all.1
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01.40.gb Teaching methods and strategies
01.40.gf Theory of testing and techniques

Physics Thirst? A Survey of Ninth‐Grade Physics Students

Boris Korsunsky and Grace Huckins

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 208

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In 2008, this magazine ran an article1 describing the results of a survey of the eighth‐graders who were about to begin their first physics course at Weston High School. The results helped this coauthor (BK) and his high school colleagues better understand the expectations of the incoming students. It seemed useful, however, to conduct another survey—one that would probe the attitudes and the perceptions of our ninth‐graders who were actually taking physics. That survey was conducted in June 2010 by BK and GH (the latter, at the time, was a sophomore enrolled in BK's Advanced Placement® Physics C course).
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01.40.ek Secondary school
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Helium Speech: An Application of Standing Waves

Christopher D. Wentworth

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 212

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Taking a breath of helium gas and then speaking or singing to the class is a favorite demonstration for an introductory physics course, as it usually elicits appreciative laughter, which serves to energize the class session. Students will usually report that the helium speech “raises the frequency” of the voice. A more accurate description of the phenomenon requires that we distinguish between the frequencies of sound produced by the larynx and the filtering of those frequencies by the vocal tract. We will describe here an experiment done by introductory physics students that uses helium speech as a context for learning about the human vocal system and as an application of the standing sound‐wave concept. Modern acoustic analysis software easily obtained by instructors for student use allows data to be obtained and analyzed quickly.
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01.40.gb Teaching methods and strategies
43.10.Sv Education in acoustics, tutorial papers of interest to acoustics educators
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

‘It Has to Go Down a Little, in Order to Go Around’ — Revisiting Feynman on the Gyroscope

Svilen Kostov and Daniel Hammer

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 216 | Cited 1 time

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In this paper we show that with the help of accessible, teaching‐quality equipment, some interesting and important details of the motion of a gyroscope, which are typically overlooked in introductory courses, can be measured and compared to theory. We begin by deriving a simple relation between the dip angle of a gyroscope released from rest and its precession velocity. We then describe an experiment that measures these parameters. The data are in excellent agreement with the theoretical prediction. The idea for this project was suggested by the discussion of gyroscopic motion in The Feynman Lectures on Physics. Feynman's (Fig. 1) conclusion (stated in colloquial language and quoted in the title) is confirmed and, in addition, conservation of angular momentum, which underlies this effect, is quantitatively demonstrated.
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01.40.gf Theory of testing and techniques
01.50.My Demonstration experiments and apparatus
07.10.-h Mechanical instruments and equipment
45.20.df Momentum conservation
45.40.Cc Rigid body and gyroscope motion

Special Relativity in Week One: 2) All Clocks Run Slow

Elisha Huggins

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 220 | Cited 4 times

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In our initial article on teaching special relativity in the first week of an introductory physics course, we used the principle of relativity and Maxwell's theory of light to derive Einstein's second postulate (that the speed of light is the same to all observers).1 In this paper we study thought experiments involving a light pulse clock moving past us with uniform motion at a speed v. Using Einstein's second postulate and the Pythagorean theorem, we see that the light pulse clock runs slow by a factor √1 − v2/c2. We then show that it is a direct consequence of the principle of relativity that all clocks moving by us the same way run slow by precisely the same factor.
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01.50.Kw Techniques of testing
06.30.Ft Time and frequency
04.20.Jb Exact solutions

Harnessing Students' Interest in Physics with Their Own Video Games

Christopher Like

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 222

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Many physics teachers assign projects where students are asked to measure real‐world motion. One purpose of this student‐centered activity is to cultivate the relevance of physics in their lives. Typical project topics may include measuring the speed of a student's fastball and calculating how much reaction time batters are given. Another student may find the trajectory of her dive off the blocks at the pool and its effect on race time. Leaving the experimental design to the student's imagination allows for a variety of proposals ranging from stopwatches to highly technical video analysis. The past few years have shown an increase in students' eagerness to tackle the physics behind the motion of virtual characters and phenomena in their own video games. This paper puts forth a method of analyzing the physics behind bringing the games students are playing for enjoyment into the physics classroom.
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01.50.ff Films; electronic video devices
01.40.gf Theory of testing and techniques
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Cramster: Friend or Foe?

Michael Grams

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 225 | Cited 1 time

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Recently when teaching a first‐semester calculus‐based physics course for engineers, I was perplexed by a particular group of students. These individuals were able to solve nearly every homework problem assigned from the end‐of‐chapter exercises in our textbook, and in some cases were able to do so using methods that we had not covered in class. However, they were unable to explain the steps in their solutions and when given similar problems on exams they performed very poorly. I became suspicious that these students were submitting homework solutions that were not their own, and a quick Internet search confirmed my fears. These students had been plagiarizing their homework assignments from a website called Cramster (www.cramster.com). In this article I would like to discuss the website, what some of my previous students and fellow educators think about it, and also consider whether or not Cramster could be useful in helping students learn physics.
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02.30.Vv Operational calculus
01.40.G- Curricula and evaluation
89.20.Hh World Wide Web, Internet

Inexpensive Instruments for a Sound Unit

Bob Brazzle

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 228

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My unit on sound and waves is embedded within a long‐term project in which my high school students construct a musical instrument out of common materials. The unit culminates with a performance assessment: students play the first four measures of “Somewhere Over the Rainbow”—chosen because of the octave interval of the first two notes—in the key of C, and write a short paper describing the theory underlying their instrument. My students have done this project for the past three years, and it continues to evolve. This year I added new instructional materials that I developed using a freeware program called Audacity.1 This software is very intuitive, and my students used it to develop their musical instruments. In this paper I will describe some of the inexpensive instructional materials in my sound unit, and how they fit with my learning goals.
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01.50.My Demonstration experiments and apparatus
43.75.-z Music and musical instruments

Teaching the First Law of Thermodynamics via Real‐Life Examples

Wheijen Chang

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 231

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The literature has revealed that many students encounter substantial difficulties in applying the first law of thermodynamics. For example, university students sometimes fail to recognize that heat and work are independent means of energy transfer.1 When discussing adiabatic processes for an ideal gas, few students can correctly refer to the concept of “work” to justify a change in temperature.1 Some students adopt the notion that “collisions between molecules produce heat” to explain the rise in temperature for an adiabatic compression process.2 When explaining processes entailing temperature variation, students tend to adopt the ideal‐gas law.1,2 Although most university students have acquired a reasonable grasp of the state‐function concept, which is valid for variation of internal energy, they fail to grasp the concept that work depends not only on the states but also the processes. Thus, they are unable to use the first law effectively.3 In order to help students comprehend the meaning, usages, and value of the first law, and to realize that the ideal‐gas law itself is insufficient to analyze many real‐life examples, this paper introduces four examples, some of which can be demonstrated in the classroom. The examples have been devised and gradually modified over a period of several years based on implementation in a calculus‐based introductory physics course. Details of when, how, and why each example is adopted, along with the students' pitfalls, are described below.
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01.40.gb Teaching methods and strategies
01.50.My Demonstration experiments and apparatus
02.30.Vv Operational calculus
05.70.-a Thermodynamics

Can a String's Tension Exert a Torque on a Pulley?

Dennis E. Krause and Yifei Sun

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 234

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A typical textbook problem in rotational dynamics involves calculating the angular acceleration of a massive pulley due to a string, such as in the example shown in Fig. 1. The string is assumed to be massless and to move without slipping over the pulley, which is mounted on a frictionless axle. If TL and TR are the tensions pulling at the left and right edges of the pulley (see Fig. 1), respectively, the net torque on the pulley is then τnet = (TL ‐ TR)R, where R is the radius of the pulley. (It is assumed that positive torque corresponds to the counterclockwise direction.) While this analysis, which is typical of what is found in many introductory physics texts,1 is correct, it should raise several questions in the mind of a student. First, since most texts argue that the tension everywhere in a massless string is constant,2 why is TL ≠ TR? Second, since tension is an internal force (except at the ends of the string, which are obviously not tied to the pulley),3 how can tension exert a force and torque on a pulley? In this paper, we will address these questions, which are overlooked in most textbook treatments of this problem whose approach appears inconsistent with the concepts presented elsewhere in the text.
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01.50.Kw Techniques of testing
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

A Mechanical Analogue of the Refracting Telescope

Maurizio Vannoni, Giuseppe Molesini, Andrea Sordini, and Samuele Straulino

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 236

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The recent celebration of the discoveries made by Galileo four centuries ago has attracted new attention to the refracting telescope and to its use as an instrument for the observation of the night sky.1 This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a key concept that is faced is magnification. In geometrical optics, the treatment of magnification is generally given in terms of light rays and first‐order (Gaussian or paraxial) ray tracing. Computer programs are available with which the light path through the lenses and the whole telescope can be simulated.
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01.50.Pa Laboratory experiments and apparatus
07.60.-j Optical instruments and equipment
42.25.Gy Edge and boundary effects; reflection and refraction

Stunt Barbie ‐ A Laboratory Practicum Combining Constant Velocity and Constant Acceleration

Scott Hertting

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 238

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In preparing to teach the advanced physics course at my high school, I found it useful to work through the end‐of‐chapter problems in the book1 used by the advanced class. A problem on motion in one dimension involved a stunt woman in free fall from a tree limb onto a horse running beneath her.2 The problem presents a connected learning opportunity for students because it requires the use of the constant velocity model xf = v∗t + xi and the constant acceleration model yf = ½∗ g∗ t2 + vyi∗ t + yi (where g = 9.8 m/s/s) to solve it. I named the stunt woman Barbie and created an activity titled “Stunt Barbie.”
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01.40.gb Teaching methods and strategies
01.50.My Demonstration experiments and apparatus

The Opaque Projector: The Inverse of the Camera Obscura

Thomas B. Greenslade, Jr.

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 241

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Many years ago I was running the standard laboratory experiment on thin lens optics. The source was the usual self‐illuminated object mounted on an optical bench, and a converging lens formed a real image on a screen. One of the students sitting near one wall of the darkened lab was having some trouble with the idea of image formation. Her face was lit by the light from a shaded gooseneck lamp, and as she looked at me holding the lens in my hand, the inverted image of her face appeared on a nearby wall. And, the image was in color! Not only was this a classic teaching moment, but I realized that, by chance, we had set up an opaque projector.
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01.50.Pa Laboratory experiments and apparatus
42.79.-e Optical elements, devices, and systems

Engineering Design Modules as Physics Teaching Tools

Douglas L. Oliver and Jackie Kane

The Physics Teacher -- April 2011 -- Volume 49, Issue 4, pp. 242

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Pre‐engineering is increasingly being taught as a high school subject. This development presents challenges as well as opportunities for the physics education community. If pre‐engineering is taught as a separate class, it may divert resources and students from traditional physics classes. However, design modules can be used as physics teaching tools that can seamlessly integrate technology, engineering, and math into high school physics using a variety of teaching styles. This paper discusses a rationale for using design modules as tools for teaching physics. As an illustration, an example of an engineering design module is presented. This example module is appropriate for an algebra‐based physics class that covers Ohm's law.
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01.40.gb Teaching methods and strategies
01.40.ek Secondary school
02.10.-v Logic, set theory, and algebra
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