The Physics Teacher

During the 17th century the idea of an orbiting and rotating Earth became increasingly popular, but opponents of this view continued to point out that the theory had observable consequences that had never, in fact, been observed. Why, for instance, had astronomers failed to detect the annual parallax of the stars that must occur if Earth orbits the Sun? To address this problem, astronomers of the 17th and18th centuries sought to measure the annual parallax of stars using telescopes. None of them succeeded. Annual stellar parallax was not successfully measured until 1838, when Friedrich Bessel detected the parallax of the star 61 Cygni. But the early failures to detect annual stellar parallax led to the discovery of a new (and entirely unexpected) phenomenon: the aberration of starlight. This paper recounts the story of the discovery of stellar aberration. It is accompanied by a set of activities and computer simulations that allow students to explore this fascinating historical episode and learn important lessons about the nature of science.

This article describes measurement of potato cannon velocity with a digitized microphone signal. A microphone is attached to the potato cannon muzzle and a potato is fired at an aluminum target about 10 m away. The potato's flight time can be determined from the acoustic waveform by subtracting the time in the barrel and time for sound to return from the target. The potato velocity is simply the flight distance divided by the flight time.

At the beginning of a class or meeting an icebreaker activity is often used to help loosen the group and get everyone talking. Our motivation is to develop activities that serve the purpose of an icebreaker, but are designed to enhance and supplement a science-oriented agenda. The subject of this article is an icebreaker activity related to gravitational wave astronomy. We first describe the unique gravitational wave signals from three distinct sources: monochromatic binaries, merging compact objects, and extreme mass ratio encounters. These signals form the basis of the activity where participants work to match an ideal gravitational wave signal with noisy detector output for each type of source. Comment: Accepted to The Physics Teacher. Original manuscript divided into two papers at the request of the referee. For a related paper on gravitational wave observatories see physics/0509201

We propose a unified approach to addition of resistors and capacitors such that the formulae are always simply additive. This approach has the advantage of being consistent with the intuition of the students. To demonstrate our point of view, we re-work some well-known end-of-the-chapter textbook problems and propose some additional new problems. Comment: 13 pages, LaTeX, uses additional packages, 7 eps figures; one comment added after the truncated-cone resistor

We comment of the widespread belief among some undergraduate students that the amplitude of any harmonic oscillator in the presence of any type of friction, decays exponentially in time. To dispel that notion, we compare the amplitude decay for a harmonic oscillator in the presence of (i) viscous friction and (ii) dry friction. It is shown that, in the first case, the amplitude decays exponentially with time while in the second case, it decays linearly with time. Comment: 3 pages, 1 figure, accepted in Phys. Teach

Two simple, interpolatory-like linearizations are shown for the simple pendulum which can be used for any initial amplitude. Comment: 6 pages, 1 figure

What can physics students learn about science from those scientists who got the answers wrong? Students encounter little science history, and what they have encountered typically portrays scientists as The People with the Right Answers. But those who got the wrong answers can teach students that in science answers are often elusive -- not found in the back of a book or discovered in a bold stroke of genius. Giovanni Battista Riccioli, a 17th-century astronomer who argued that science supported a geocentric universe, and whose arguments made sense given the knowledge of the time -- is an example of such a person.

It is well known that the length and orientation of a shadow cast by a vertical gnomon depends on the time of the day and on the season of the year. But it also depends on the latitude of the site of observation. During the equinoxes, the temporal sequence of the shadows cast by each of the points that form any object follows a straight line from west to east. A simple construction using sticks and threads can be used to materialize the plane of celestial equator's local projection, giving us a way to calculate our astronomical latitude during daytime with high precision.

This article reviews the current status of gravitational wave astronomy and explains why astronomers are excited about the new generation of gravitational wave detectors. As part of the review we compare and contrast gravitational radiation to the more familiar electromagnetic radiation. We discuss the current indirect experimental evidence for gravitational waves, and how current and future gravitational wave detectors will operate as our newest telescopes pointed at the skies. Comment: See related hands-on activity at physics/0503198. Accepted to The Physics Teacher

Three current topics in astrophysics are described here on the occasion of the joint meeting of the American Association of Physics Teachers and the American Astronomical Society (Jan. 7-11, 2001, San Diego, Calif.). Many equally exciting topics--ranging from the dozens of newly discovered planets of sunlike stars to evidence suggesting that the expansion of the universe is accelerating--could have been chosen. The topics discussed are: (1) the habitability of Mars, (2) black holes, galaxy bulges, and the X-ray background, and (3) the greatest explosions since the Big Bang.

Have you ever observed a child playing with toy blocks? A favorite game is to build towers and then make them topple like falling trees. To the eye of a trained physicist this should immediately look like an example of the physics of “falling chimneys,” when tall structures bend and break in mid-air while falling to the ground. The game played with toy blocks can actually reproduce well what is usually seen in photographs of falling towers, such as the one that appeared on the cover of the September 1976 issue of The Physics Teacher.¹ In this paper we describe how we performed and analyzed these simple but interesting experiments with toy blocks.

We present an inexpensive apparatus for measuring the speed of sound, with a time of flight method, using a computer with a stereo sound board. Students measure the speed of sound by timing the delay between the arrivals of a pulse to two microphones placed at different distances from the source. It can serve as a very effective demonstration, providing a quick measurement of the speed of sound in air; we have used it with great success in Open Days in our Department. It can also be used for a full fledged laboratory determination of the speed of sound in air. Comment: Accepted for publication in The Physics Teacher

Experiments in mechanics often involve measuring time intervals much smaller than one second, a task that is hard to perform with handheld stopwatches. This is one of the reasons why photogate timers are so popular in school labs. There is an interesting alternative to stopwatches and photogates, easily available if one has access to a personal computer with sound‐recording capability. The idea is simple: a computersound card can record audio frequencies up to several kilohertz, which means it has a time resolution of a fraction of a millisecond, comparable to that of photogate timers. Many experiments in mechanics can be timed by the sound they produce, and in these situations a direct audio recording may provide accurate measurements of the time intervals of interest. This idea has already been explored in a few cases,1–5 and here we apply it to an experiment that our students found very enjoyable: measuring the speed of soccer balls they kicked.

Recently, a simple and very low-cost photogate has been shown by Horton (Phys. Teach. 48, 615, December 2010) as an efficient experimentation tool in physics education. The photogate connects to the microphone input of a personal computer and a free software can be used to visualize the light interruptions caused by a moving object like a pendulum. Although the device works properly, there are further possibilities of improvement and similar alternatives also exist. The following brief review may help teachers to pick the one that best fits their needs and possibilities.

Many instructors choose to assess their students using open-ended written exam items that require students to show their understanding of physics by solving a problem and/or explaining a concept. Grading these items is fairly time consuming, and in large courses time constraints prohibit providing significant individualized feedback on students' exams. Instructors typically cross out areas of the response that are incorrect and write the total points awarded or subtracted. Sometimes, instructors will also write a word or two to indicate the error. This paper describes a grading method that provides greater individualized feedback, clearly communicates to students expected performance levels, takes no more time than traditional grading methods for open-ended responses, and seems to encourage more students to take advantage of the feedback provided.

Causality in electrodynamics is a subject of some confusion, especially regarding the application of Faraday's law and the Ampere-Maxwell law. This has led to the suggestion that we should not teach students that electric and magnetic fields can cause each other, but rather focus on charges and currents as the causal agents. In this paper I argue that fields have equal status as casual agents, and that we should teach this. Following a discussion of causality in classical physics I will use a numerical solution of Maxwell's equations to inform a field based causal explanation in electrodynamics.

In this paper I describe an in-class discussion activity aimed at helping elementary education majors in a physical science course think about issues surrounding the inclusion of "Intelligent Design" in public school science standards. I discuss the background instruction given, the content of the activity and some results from its use in class.

Using a personal computer and a smartphone, iMecaProf is a software that provides a complete teaching environment for practicals associated to a Classical Mechanics course. iMecaProf proposes a visual, real time and interactive representation of data transmitted by a smartphone using the formalism of Classical Mechanics. Using smartphones is more than using a set of sensors. iMecaProf shows students that important concepts of physics they here learn, are necessary to control daily life smartphone operations. This is practical introduction to mechanical microsensors that are nowadays a key technology in advanced trajectory control. First version of iMecaProf can be freely downloaded. It will be tested this academic year in Universit\'e Joseph Fourier (Grenoble, France)

We describe a simple, low-cost experiment and corresponding pedagogical strategies for studying fluids whose viscosities depend on shear rate, referred to as non-Newtonian fluids. We developed these materials teaching for the Compass Project, an organization that fosters a creative, diverse, and collaborative community of science students at UC Berkeley. Incoming freshmen worked together in a week-long, residential program to explore physical phenomena through a combination of conceptual model-building and hands-on experimentation. During the program, students were exposed to three major aspects of scientific discovery: developing a model, testing the model, and investigating deviations from the model.

With advocates like Sal Khan and Bill Gates, flipped classrooms are attracting an increasing amount of media and research attention. We had heard Khan's TED talk and were aware of the concept of inverted pedagogies in general. Yet, it really hit home when we accidentally flipped our classroom. Our objective was to better prepare our students for class. We set out to effectively move some of our course content outside of class and decided to tweak the Just-in-Time-Teaching approach (JiTT). To our surprise, this tweak - which we like to call the flip-JiTT - ended up completely flipping our classroom. What follows is narrative of our experience and a procedure that any teacher can use to extend JiTT to a flipped classroom.

We propose an experiment for investigating how objects cool down toward the thermal equilibrium with its surrounding through convection. We describe the time dependence of the temperature difference of the cooling object and the environment with an exponential decay function. By measuring the thermal constant tau, we determine the convective heat-transfer coefficient, which is a characteristic constant of the convection system.

The Physics First movement - teaching a true physics course to ninth grade students - is gaining popularity in high schools. There are several different rhetorical arguments for and against this movement, and it is quite controversial in physics education. However, there is no actual evidence to assess the success, or failure, of this substantial shift in the science teaching sequence. We have undertaken a comparison study of physics classes taught in ninth- and 12th grade classes in Maine. Comparisons of student understanding and gains with respect to mechanics concepts were made with excerpts from well-known multiple-choice surveys and individual student interviews. Results indicate that both populations begin physics courses with similar content knowledge and specific difficulties, but that in the learning of the concepts ninth graders are more sensitive to the instructional method used.

We develop a new method to determine the acceleration of a block sliding down along the face of a moving wedge. We have been able to link the solution of this problem to that of the inclined plane problem of elementary physics, thus providing a simpler solution to it. Comment: 4 pages, 3 figures

The fundamental physical implications of the possible detection of massive neutrinos are discussed, with an emphasis on the Grand Unified Theories (GUTs) of matter. The Newtonian and general-relativistic pictures of the fundamental forces are compared, and the reduction of electromagnetic and weak forces to one force in the GUTs is explained. The cosmological consequences of the curved-spacetime gravitation concept are considered. Quarks, leptons, and neutrinos are characterized in a general treatment of elementary quantum mechanics. The universe is described in terms of quantized fields, the noninteractive 'particle' fields and the force fields, and cosmology becomes the study of the interaction of gravitation with the other fields, of the 'freezing out' of successive fields with the expansion and cooling of the universe. While the visible universe is the result of the clustering of the quark and electron fields, the distribution of the large number of quanta in neutrino field, like the mass of the neutrino, are unknown. Cosmological models which attribute anomalies in the observed motions of galaxies and stars to clusters or shells of massive neutrinos are shown to be consistent with a small but nonzero neutrino mass and a universe near the open/closed transition point, but direct detection of the presence of massive neutrinos by the UV emission of their decay is required to verify these hypotheses.

A miniature drop tower, Reduced-Gravity Demonstrator is developed to illustrate the effects of gravity on a variety of phenomena including the way fluids flow, flames burn, and mechanical systems (such as pendulum) behave. A schematic and description of the demonstrator and payloads are given, followed by suggestions for how one can build his (her) own.

Recently much attention has been paid to the discovery of Hubble's law: the linear relation between the rate of recession of the distant galaxies and distance to them. Though we now mention several names associated with this law instead of one, the motivation of each remains somewhat obscure. As it is turns out, two major contributors arrived at their discoveries from erroneous reasoning, thus making a case for a Type III error. It appears that G. Lemaitre (1927) theoretically derived Hubble's Law due to his choice of the wrong scenario of the Universe's evolution. E. Hubble (1929) tested the linearity law not based on Lemaitre's non-static model, but rather a cumbersome extension of de Sitter's static theory proposed by H. Weyl (1923) and L. Silberstein (1924).

Our aim in this proposal is to use Faraday's law of induction as a simple lecture demonstration to measure the Earths magnetic field (B). This will also enable the students to learn about how electric power is generated from rotational motion. Obviously the idea is not original, yet it may be attractive in the sense that no sophisticated devices are used. All the equipment needed is available in an elementary physics laboratory and is displayed in Fig. 1. The square wooden coil and handmade belt system to rotate the coil may require some craftsmanship; once made, it can be used for years. Using a compass, we first orient the table parallel to the direction of the Earth's horizontal component of B field. This is necessary to maximize the Earth's field which can suppress the noise effects as much as possible. It is preferable to minimize also any environmental effects by conducting the experiment away from power lines, if possible of course.

We describe an initiative at the University of Bonn, where the students develop and perform a 2 hour physics show for school classes and the general public. The show is entertaining and educational and is aimed at children aged 10 and older. For the physics students this is a unique experience to apply their knowledge at an early stage and gives them the chance to develop skills in the public presentation of science, in front of 520 people per show. We have extended the activity to put on an elementary particle physics show for teenagers. Furthermore, local high schools have picked up the idea; their students put on similar shows for fellow students and parents. We would be interested in hearing about related activities elsewhere. Comment: 6 Pages, LateX, 3 Figures. High quality figures available from author. Journal submission notice added

We describe students revising the mathematical form of physics equations to match the physical situation they are describing, even though their revision violates physical laws. In an unfamiliar air resistance problem, a majority of students in a sophomore level mechanics class at some point wrote Newton's Second Law as F = -ma; they were using this form to ensure that the sign of the force pointed in a direction consistent with the chosen coordinate system while assuming that some variables have only positive value. We use one student's detailed explanation to suggest that students' issues with variables are context-dependent, and that much of their reasoning is useful for productive instruction.

Physlets are scriptable Java applets that can be used for physics instruction. In this article we discuss the pedagogical foundations of Physlet use and provide a sample of Physlet-based exercises that could be used to teach optics. Comment: Published in The Physics Teacher, November 2002, pp. 494-499. 9 pages, 7 figures

We present an elementary discussion of two basic properties of angular displacements, namely, the anticommutation of finite rotations and the commutation of infinitesimal rotations, and show how commutation is achieved as the angular displacements get smaller and smaller.

In 1785 astronomer William Herschel mapped out the shape of the Milky Way star system using measurements he called "star-gages." Herschel's star-gage method is described in detail, with particular attention given to the assumptions on which the method is based. A computer simulation that allows the user to apply the star-gage method to several virtual star systems is described. The simulation can also be used to explore what happens when Herschel's assumptions are violated. This investigation provides a modern interpretation for Herschel's map of the Milky Way and why it failed to accurately represent the size and shape of our galaxy.

Sports are a popular and effective way to illustrate physics principles. Baseball in particular presents a number of opportunities to motivate student interest and teach concepts. Several articles have appeared in this journal on this topic, illustrating a wide variety of areas of physics. In addition, several websites and an entire book are available. In this paper we describe a student-designed project that illustrates the relative surface gravity on the Earth, Sun and other solar-system bodies using baseball. We describe the project and its results here as an example of a simple, fun, and student-driven use of baseball to illustrate an important physics principle.

Are we smarter now than Socrates was in his time? Society as a whole certainly enjoys a higher degree of education, but humans as a species probably don't get intrinsically smarter with time. Our knowledge base, however, continues to grow at an unprecedented rate, so how then do we keep up? The printing press was one of the earliest technological advances that expanded our memory and made possible our present intellectual capacity. We are now faced with a new technological advance of the same magnitude--the internet--but how do we use it effectively? A new tool is available on Google (http://www.google.com) that allows a user not only to numerically evaluate equations, but to automatically perform unit analysis and conversion as well, with most of the fundamental physical constants built in. Comment: 4 pages, 2 figures, 1 Table. Appropriate for high school physics

In science new words might be “invented” to name or describe new processes, discoveries, or inventions. However, for the most part, the scientific vocabulary is formed from words we use throughout our lives in everyday language. When we begin studying science we learn new meanings of words we had previously used. Sometimes these new meanings may contradict everyday meanings or seem counterintuitive. We often learn words in association with objects and situations.1 Due to these associations that students bring to class, they may not interpret the physics meaning correctly. This misinterpretation of language leads students to confusion that is sometimes classified as a misconception.2–6 Research about the semantics used in physicstextbooks7–9 and the meaning of words has been done,10–12 but the problem seems to go beyond semantics.8 The linguistic relativity hypothesis, sometimes referred to as the Sapir-Whorf hypothesis,1 says that “we see and hear and otherwise experience very largely as we do because the language habits of our community predispose certain choices of interpretation.” An upshot of this hypothesis is that language may not determine thought, but it certainly may influence thought. 1 We have to make students conscious of the fact that though the words may remain the same, their everyday meaning is no longer a figure of speech, but a technical meaning (physics meaning). That is, we need to change the way students may “think” about words. In spite of the close relationship between language and thought, most research does not address the semantics used in physicstextbooks7–9 and the meaning of words.10–12 This study, however, will address that relationship.

In this paper, I outline some problems in the students' understanding of the explanation of recoil motion when introduced to them in the context of Newton's third law. I propose to explain the origin of recoil from a microscopic point of view, which emphasizes the exact mechanism leading to recoil. This mechanism differs from one system to another. Several examples that can be easily implemented in the classroom environment are given in this paper. Such a profound understanding of the origin of recoil help students avoid some of the misconceptions that might arise from the phenomenological approach, and stimulates their thinking in the fundamental origins of other physical phenomena.

We report on our study of student understanding of the physics of mechanical waves, specifically the propagation and superposition of simple wavepulses traveling on long, taut strings. We introduce the terms "particle pulses mental model" to describe the reasoning approach that students use to guide their thinking in wave propagation and superposition. Student responses on free response and multiple-choice, multiple response questions dealing with the same physics show inconsistent student thinking, where they may have both correct and incorrect ideas about the concepts. Comment: 8 pages, 6 figures, 3 tables, 10 references and notes

I discuss the precession motion of a symmetrical top without the assumption that its precessional velocity is much smaller than its spin angular velocity. I derive the general formula for the precessional velocity in an elementary way and discuss the cases of slow and fast precessions. Comment: latex, 2 pages, 2 figures

If one asked some friends where on the horizon they should expect to see the sunrise, half of the answers would be "in the east". 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.

Magnetic levitation is a way of using electromagnetic fields to levitate objects without any noise. It employs diamagnetism, which is an intrinsic property of many materials referring to their ability to temporarily expel a portion of an external magnetic field. As a result, diamagnetic materials are repelled by strong magnetic fields. This repulsive force, however, is very weak compared with the attractive force due to magnetic fields. Maglev is the means of floating one magnet over another. This maglev system is divided into two types attractive systems and repulsive systems, which are referred to as electromagnetic suspension and electrodynamics suspension. Thus many countries spend billions of dollars to use this maglev system.

this paper differs from previous work mainly in that precisely the MAP estimate of the model is found, where usually the MAP estimate of the model together with the denoised data points is computed or approximated. Also, we extend the fitting to the general, nonparametric case

Animation has become enormously popular in feature films, television, and video games. Art departments and film schools at universities as well as animation programs at high schools have expanded in recent years to meet the growing demands for animation artists. Professional animators identify the technological facet as the most rapidly advancing (and now indispensable) component of their industry. Art students are keenly aware of these trends and understand that their future careers require them to have a broader exposure to science than in the past. Unfortunately, at present there is little overlap between art and science in the typical high school or college curriculum. This article describes our experience in bridging this gap at San Jose State University, with the hope that readers will find ideas that can be used in their own schools.

The common definition is shown to be false. A modern definition must be based on the first and second laws of thermodynamics and in terms of a set of algebraic expressions written in such a way that their sum does not change when a system is isolated. (DF)

The Physics Teacher 48(8), 559 (2010) DOI: http://doi.org/10.1119/1.3502521

(1) In the first sentence under Fig. 1, the fragment "brightnesses were in proportion 9:4:1" should be substituted by "brightnesses were in proportion 36:9:4." The latter corresponds to the ratio of the distances 1:2:3 used in the first section of the paper. (2) Similarly, in the lefthand column of page 105 (the second paragraph of the "Discussion and solution"), the "ratio of brightnesses 9:4:1" should be changed to "ratio of brightnesses 36:9:4." (3) In the same paragraph "(the square roots of 1, 4 and 9)" should be changed to "(the ratio of the square roots of 1/36, 1/9, and 1/4)." I am grateful to Mr. Philip Backman for pointing out this error.

The Physics Teacher 51(7), 446 (2013) DOI: http://doi.org/10.1119/1.4820874

The Physics Teacher 45(5), 320 (2007) DOI: http://doi.org/10.1119/1.2731293