Table of contents

This article presents a simple and handy technique to measure respiration rate that employs the magnetic field sensor of a smartphone device. On the abdomen of the subject a tiny and very light permanent magnet is placed and the apparently periodic field—caused by what appears to be periodic breathing of the subject—of the magnet is recorded by the smartphone with the help of its magnetic field sensor. The acquired magnetic field signals allows for the measurement of the period, thus the breathing rate; the value obtained is well within range of normal values. The activity is seen to afford instructional significance in a physics or biology class or, to an extent, in a clinical setting.

We have developed an Arduino-based wireless measuring car that can be made manually on a budget, which is capable of performing multiple experiments involving force and motion. We also tested the car in a Newton's Second Law experiment, and the results are promising.

Understanding the cosmic microwave background, i.e. the relic radiation from the early Universe, is essential for useful insights into fundamental physics. This paper is an attempt to summarise the origin of this background, in a very comprehensive way for physics beginners.

In this work, we present a simple and affordable experiment to determine the Reynolds number for water flowing through a cylindrical aperture. Commercially available equipment exists but often at high cost. Instead, the use of simple laboratory equipment (stopwatches, measuring cylinders and plastic bottles) allows an entire class to complete the experiment simultaneously. By measuring the mean bulk flow rates and calculating a value for the mean bulk speed of the fluid the Reynolds number (Re) can be determined. Using this experimental equipment we observed both laminar and turbulent flow, as confirmed through our calculated values of Re  =  1100 300 and Re  =  9400 700 respectively. Finally, we offer practical advice for carrying out these experiments as well as suggesting suitable further activities to make this activity accessible to various levels of study.

When filming an object moving in two dimensions on a horizontal plane, perspective errors arise if the object is viewed at an oblique angle. Simple corrections can be made to obtain the correct coordinates.

An RC series circuit, incorporating readily-available components, along with interactive activities for students are discussed in order to demonstrate how the RC time constant varies with changes in resistance and/or capacitance. The circuit uses a flashing Neon bulb to visually monitor variations of the RC time constant. With the aid of a projection camera, the circuit described is ideal for use in classroom settings and requires only 1–3 min of set-up time.

Most rockets convert the energy stored in their propellant mass into the mechanical energy required to expel it as exhaust. The 'rocket equation', which describes how a rocket's speed changes with mass, is usually derived by assuming that this fuel is expelled at a constant relative velocity. However, this is a poor assumption for cases where the rocket promptly loses a large fraction of its mass. Instead, I derive the change in speed for a rocket that emits its fuel in N discrete pellets, with a constant mechanical energy produced per unit fuel mass. In this model I find that the rocket's speed change is greatest when all the fuel is expelled at once (N  =  1). In the limit of many small pellets (N  →  ∞), I show that the velocity change approaches, from above, the prediction of the continuous thrust rocket equation. For this model of rocket propulsion, I quantify how the fuel's total available energy is divided between the rocket and exhaust. In the limit of continuous thrust, the rocket can utilise no more than 65% of the available mechanical energy as its kinetic energy. In an online supplement, I compare this model of discrete propulsion with those previously published. This topic uses momentum conservation and mechanical energy concepts at the introductory undergraduate level.

Quantum physics is challenging for young students, but also a source of fascination. Observation is a key concept in order to understand how principles and experimental results in quantum physics differ from what we are used to in classical physics and everyday experiences. In this study we investigate how pre-university physics students understand the concept of observation in the case of the famous double-slit experiment with electrons and interpretations of its results. We found that a conception of observation as looking, meaning a passive registration, is prevalent among students. This causes serious problems in understanding quantum physics and leads to very unproductive speculations that links to mysticism. Some students considered observation as measurement involving some sort of apparatus, but very few expressed the key idea of measurement as interaction. We discuss how a more explicit discussion of what observation means in quantum physics can benefit students' understanding of principles in quantum physics and their philosophical consequences.

The purpose of this publication is to bring attention to some physics problems whose answers seem to be paradoxical and, at first glance, do not agree with a limiting case check. Solving a problem on the motion of a system consisting of two masses and a spring, it is natural to examine the answer by considering a case when a spring constant is going to infinity. But how do you do it if there is no spring constant in the final formula? Three situations with paradoxical answers are considered in detail in this article. To solve these paradoxes we needed to look at the motion of each system more closely and to define more precisely the mathematical model of its motion. The results of our work could be used for educational research student's projects.

Medical physics uses physics knowledge in medicine or healthcare. The question surrounding the methods of measuring temperature is important in medicine. The aim of this article is to explore the possibilities of using Microsoft Excel to study thermometers. The physical concepts and laws related to temperature measurement have been considered. The tools of Microsoft Excel allow us to visualize the results of physics experiments and provide math processing of the data collected in it. Microsoft Excel considerably reduces the time needed to create graphs and calculate physical quantities and allows one to determine physical quantities which cannot be measured directly. As a rule, any measurements have errors. In this case, the technique of evaluating errors using Microsoft Excel was proposed. Some limitations of using Microsoft Excel in the creation of graphs for nonlinear functions have been pointed and suggestions to eliminate them were made.

Most people are familiar with arc discharges through the use of simple gas lighters within the home but corona discharges are not so common. This note presents students with three simple corona discharge experiments so that they can appreciate this form of electrical discharge. Firstly, one detects whether positive or negative ions are created; secondly, one observes a faint blue light from the discharge region and thirdly, an approximate dimension is made to the extent of the discharge region.

It has become increasingly common for high-school students to see media reports on the importance of quantum mechanics in the development of next-generation industries such as drug development and secure communication, but few of them have been exposed to fundamental quantum mechanical concepts in a meaningful classroom activity. In order to bridge this gap, we design and implement a low-cost 20 min demonstration of the Bell test, which is used in several entanglement-based quantum key distribution protocols. The demonstration introduces ideas such as the quantum state, quantum measurement, spin quantization, cryptography, and entanglement; all without using concepts beyond the 9th grade of the Chilean high-school curriculum. The demonstration can serve to promote early exposure of the future adopters and developers of quantum technology with its conceptual building blocks, and also to educate the general public about the importance of quantum mechanics in modern industry.

This paper describes the use of a smartphone's sensors to investigate the motion of a torsion pendulum to demonstrate energy conservation. The smartphone was placed on and attached to a metal disk hanging by a wire. The oscillation of the disk was measured using the smartphone's sensors to simultaneously record angular position, angular speed and angular acceleration. These experimental data were processed to demonstrate mechanical energy conservation during oscillation. We expect that this smartphone-based experiment will be useful for physics teachers and can make students better understand an oscillating disk's relationship with energy conservation.

A popular physics legend holds that scissors can cut paper with a speed faster than light. Here this counter-intuitive myth is investigated theoretically using four simple examples of scissors. For simplicity, all cases will involve a static lower scissors blade that remains horizontal just under the paper. In the first case, the upper blade will be considered perfectly rigid as it rotates around and through the paper, while in the second case, a rigid upper blade will drop down to cut the paper like a guillotine. In the third case, the paper is cut with a laser rotating with a constant angular speed that is pointed initially perpendicular to the paper at the closest point, while in the fourth case, the uniformly rotating laser is pointed initially parallel to the paper. Although details can be surprising and occasionally complex, all cases allow sections of the paper to be cut faster than light without violating special relativity. Therefore, the popular legend is confirmed, in theory, to be true.

A video is taken of a road-sign mirage from the passenger seat in a car traveling at constant speed on a highway. The video spans the duration of seeing the mirage of the sign, viewing the vanishing of the mirage as the car approaches, and passing the road sign. The mirage angle, defined as the angle with respect to the horizontal at the moment the observer notes the vanishing of the mirage, can be determined from the video, the speed of the car, and known dimensions of the standard road sign. The value can be checked with a theoretical formula using the ambient weather temperament and consulting references to determine the temperature of the air in contact with the road surface. Agreement between observation and theory is within the error bounds. In the conclusion, a quick observational estimate is made in the car without needing the video.

This paper is inspired from a scene in the movie Memento (2000), where the eyeglass prescription for a myopic eye can be estimated since the virtual image of a distant wall seen through the lens and a nearby actor outside the view of the lens are located at the same distance. The estimate illustrates that there are times when the power of physics allows one to arrive at a sophisticated measured result with no equipment. This fascinating example also provides for a nice interdisciplinary connection between physics and medical optics. Due to copyright restrictions on incorporating a movie in class, teachers may use the author's photo and video included here or have their students make similar media with their smartphones.

This research aimed to measure the coefficient of restitution (COR) for tennis and golf balls using smartphone sensors. The ball and smartphone were attached at the ends of a long plastic strip: one end was a pivot with the attached smartphone and another end was for the attached ball. The ball on the plastic strip was swung to bounce the ball. The experimental data, angular position and angular speed, were recorded using a smartphone's sensors (gyroscope sensor and device motion sensor) for analysis of the COR. The results of the COR obtained from both sensors agreed with the conventional method and references. We expect this experiment to be useful for physics lecturers to demonstrate the bouncing ball in the classroom or laboratory for determining the COR.

We present an Arduino approach to collect pressure and temperature data from electronic sensors. Using a constant volume-metal-vessel immersed in a water bath and changing its temperature, we measure the pressure as a function of the temperature inside the vessel. With this apparatus, it is possible to demonstrate Gay-Lussac's law. Based on measurements of pressure and temperature we can establish the absolute Kelvin temperature scale.

A mechanical model of light propagation helps to show that optical refraction is related to the speed of light and how it changes from one medium to another. A tricycle toy robot is used to realize the model. Left and right wheels independently change their speed (high or low) in response to the local color (white or black, respectively) of the ground pattern detected by the corresponding optical sensor. Because of this simple rule the robot path deviates when passing, for example, from a clear to a dark area, in this way mimicking the refraction of a beam of light at an air–glass interface. Black silhouettes, representing optical components, are positioned on a clear mat along the robot trip. The robot trajectories reproduce phenomena such as refraction and total internal reflection showing a perfect analogy to light path described by geometrical optics in a sort of live ray-tracing.

The conical pendulum is a topic theoretically approached in physics literature, but with little experimental activity developed due to the difficulty of reproducing the conical motion in ideal experimental conditions. This work consisted of studying the motion of a rigid conical pendulum using video analysis. The experimental results were used as the basis to fit a theoretical model that allowed us to find the position of the center of mass of the pendulum.

Despite being established as genuine physical features of the universe, black holes are not well understood at a non-technical level. Basic features of black holes are outlined, a few of the more popular misconceptions surrounding them are listed and their errors identified.

Optics is one of the subject areas in which students have difficulty learning. Establishing the right connections between the concepts of optics and daily life supports the learning of the concepts of optics. In addition, this connection increases the students' motivation to learn optical issues. In this study, three activities related to prisms were performed by using spectacles to increase the connection between the subject of daily life and prisms. These activities have been proposed as real-life activities such as binoculars and a submarine periscope that can be used in the teaching of prisms.

Describing the motion in a vertical roller coaster loop requires a good understanding of Newton's laws, vectors and energy transformation. This paper describes how first-year students try to make sense of force and acceleration in this example of non-uniform circular motion, which was part of a written exam. In addition to an analysis of the exam solutions by about 60 students, a group interview was performed a couple of weeks later with four students, who had all passed the exam. The interview allowed the students to reflect on assumptions made and information missed.

In order to increase understanding of the cochlea and to illustrate its connection to basic physics, a functional model was developed. It was found to be useful in exploring the basic dynamics of the basilar membrane and its role in the frequency mapping of the cochlea.

The equivalent resistance calculation for two circuits in cubic arrangements is solved. Emphasis is placed on the plastic (topological) properties of these circuits. In contrast, the opposite topological behaviour of an analogous arrangement is observed in the calculus of a magnetic field. It is also noted that the solved examples may be used as a teaser/comic pedagogical approach to physics instruction.

This paper focuses on the potential benefits of integrating physics demonstrations as a mediator for learning the physics of sound, acoustics and psychoacoustics in an undergraduate audiology classroom. The participants of this study were 54 first-year audiology students enrolled in the Physics of Sound and Acoustics course. According to the results, students' physics achievement in a paper-pencil test (midterm exam) was found to be a good predictor for the good understanding of psychoacoustics. However, the results of a multiple regression analysis showed that student's performance in physics demonstrations also mediate the process of learning in this course.

The BBC Micro:bit is a great device to encourage students to get involved in Computer Science and to create their own digital projects. However, the design of the single-board computer (including the built-in sensors) makes it possible to use it in Physics lessons or in Physics related activities, too. Those students who are keen to take up challenges connecting to computers and programming can be motivated to learn Physics as well. The fact that Micro:bit can be programmed using a block based programming language enables teachers to introduce students with less programming experience into the world of Physical Computing. This paper presents some examples of how the Micro:bit can help improve students' skills in Physics and Computer Science in an enjoyable and successful way.

This paper was inspired by the work of a previous contributor on the subject of modelling plague epidemiology by comparing it to the physics of series radioactive decay, RC transients, and fluid dynamics. An Arduino-based experiment to illustrate the fluid-dynamical case is described. Attention is drawn to important differences between systems which at first sight appear to be analogs of one another.

Introductory electricity is a difficult topic for most lower secondary students, especially the development of an adequate conceptualisation of voltage is seen as a major obstacle. A few instructional concepts concerning the teaching and learning of physics have been proven helpful when it comes to constructing conceptual knowledge. For example, the choice of content structure, meaningful elementarisation of basic concepts or adequate use of analogies. What has not been in the focus is how physics school textbooks consider these factors. In this article, we compare four widely used Austrian physics school textbooks concerning their content structure, definition of basic concepts and their use of analogies. Results show that the concept of 'content structure diagrams' is a useful tool to analyse schoolbooks. Although Austria has a compulsory syllabus, the four schoolbooks greatly differ in the amount of covered content and interlinking of concepts. However, a few common approaches regarding the sequencing of the concepts were identified and are reported in this article.

People today shouldn't be surprised to find out an experiment, reported today as Rutherford's, never had his name on the original paper. He always gave young colleagues the kudos and only put his name on the paper if he had carried out a lot of the experimental work, even when he had been the first to earlier observe the effect, had proposed the topic, and had directed its execution.

A brief reply to Prof. Campbell's comment follows below.

In this letter, we point to the unusual electric property of metals relevant to the paper "The mysteries of conductive thread: physics and engineering combined" that we wrote earlier.

Some simple experiments looking at the images produced in plane mirrors.

What happens to the frequency when bottles containing different gases are blown to create a sound?