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An Instructive Apparatus for Determining the Density of Liquids Based on Archimedes’ Principle
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| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 114–115 |
| Abstrak | : | Density is an important property in various fields; for example, it is used in the quality control of chemical and food products, and in the determination of the alcohol content in beers. In medicine, an anomalous urine density may indicate certain diseases, or an anomalous blood density, anemia. Among the most modern instruments for determining the density of liquids, the vibrating-tube densimeter is the most widely used, mainly in the petroleum industry.1 In this paper, we propose an experimental activity, which is appropriate for high school and first-year university physics students, in which the density of various liquids, such as saturated aqueous NaCl, tap water, soy oil, or 70% alcohol, is determined. The apparatus required for the experiment is an acrylic box, a syringe, four coins, and water, and the students should be familiar with Archimedes’ principle and graphical analysis. |
The Relative Motion When Accelerating the Container of an Object Submerged in a Fluid
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 110-112 |
| Abstrak | : | When asked about the acceleration of an object thrown upward at the moment it reaches its apex, many students answer zero. Situations that can cause conflict with misconceptions shared by many students have been very beneficial for physics education. If one end of a string is fixed to the inside bottom of a bottle containing water and a Styrofoam ball is suspended, submerged in the water, at the other end, and the water bottle is pushed by hand, thereby accelerating it to the left, in which direction will the submerged Styrofoam ball move? Most students might say that the force of inertia causes it to move to the right (in the direction opposite the bottle’s acceleration) in the moving frame. Most students give the wrong answer because they remember inertia only. We implemented this experiment, and we observed the Styrofoam ball moving to the left relative to the water. |
Acceleration in the City
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 108-109 |
| Abstrak | : | The concept of acceleration can be challenging for students to understand when learning about the physics of translational motion.1,2 For instance, in acceleration vs. time graphs, a decrease in positive acceleration can easily be misinterpreted as a decrease in velocity, rather than as a slower rate of increase in velocity. For use as a resource bank for teaching about acceleration in introductory physics, we obtained acceleration vs. time data for various forms of transportation encountered in the city of Philadelphia. Data were obtained using a mountable USB-device accelerometer and were compiled by the authors. The collection included data for transportation by subway, trolley, bus, automobile, train, airplane, and bicycle. Using these plots, students have the opportunity to develop skill in interpreting acceleration vs. time data, and to learn about the scale and variation of translational acceleration that is operative in everyday experience. The full data collection (28 figures) is... |
Deep in Galileo’s Groove Open Access
| Pengarang | : | Lachlan West |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 104-107 |
| Abstrak | : | Here, the acceleration of a ball rolling down a gently inclined V-shaped channel has been measured in two experiments: one using manual release with stopwatch timing and the other a mechanical release with higher-precision electronic timing. The two methods produced results with little difference. In contrast to Galileo’s description of the experiment, where a “shallow” groove is used to keep the ball traveling on a straight path, the ball here travels “deep” in the groove in the sense that the walls of the channel extend beyond the points of contact. In this case, the results are independent of ball radius. In most practical versions of the inclined plane, including Galileo’s, the ball rolls down the plane guided by a groove to prevent deviations from a straight-line path. Unfortunately, Galileo himself did not fully grasp how the rotation affects the analysis of the results,1 and the details remain an interesting area of investigation. As originally described, the key result—that velocity changes by the same increments in equal time intervals and hence displacement increases as the square of the time taken—was found to be independent of the angle of the incline. Galileo wrote that “we always found that the spaces traversed were to each other as the squares of the times, and this was true for all inclinations of the plane”2,3; however, unless the steepest allowable angle is specified, this statement is overly general. The ball rolls without slipping only for sufficiently small angles.4–7 There are other significant differences induced by the rolling. If we change the shape of the body or its mass distribution, neither will affect free fall in a vacuum, but both change the times of descent on an inclined plane. Further, if the depth of the groove is changed, these times will also be affected, since the energy balance between the rectilinear and rotational components of the motion changes. There is no such parameter to change for freely falling bodies since in the absence of air resistance, there is no torque, and an arbitrary horizontal velocity (or rotational velocity) does not change the vertical acceleration due to gravity. The theoretical expectations for a combination of rolling and rectilinear motion are given in standard physics textbooks,8 but we generalize the theory in Appendix A9 to include a groove of arbitrary depth. In previous versions of the experiment, the groove is shallow in the sense that the contact points on the ball are close together in comparison to the ball diameter, and the presence of the groove is treated as a correction. In the present experiment with a deep groove, the distance between the two contact points is maximal for the given groove geometry. We have chosen a right-angled channel for the experimental measurements as this is likely to be the most readily available and relevant in a pedagogic context, where the cost of apparatus is a consideration. However, the more general theory suggests interesting variations (see Appendix A).9 In a teaching laboratory, the usual aim is to obtain optimal results with limited means, and it might be assumed that measurements performed manually, i.e., with rulers or tape measures and stopwatches, are not as good as measurements that minimize or eliminate human intervention. In the present work, we put the emphasis on manual skills and use instrumentation to check the quality of the results so that the source of departures from theory can be understood correctly. The point here is to demonstrate that the main deviation from theory is not due to any deficiency in manual timing, provided that the student develops and applies the requisite skills to make good measurements. |
The Physics of a Rope Dart: Mass, Force, and Circular Motion
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 100-103 |
| Abstrak | : | The rope dart (or meteor) is a flexible weapon originating in Chinese martial arts. It consists of a long rope or chain (2.5–6?m in different variations) with a metal dart attached to its end. The dart can be replaced by a soft weight usually intended for practicing, as shown in Fig. 1. Nowadays, the rope dart has gone beyond the scope of martial arts, becoming a subgenre in circus and dancing disciplines. Rope dart performance techniques are based mainly on the physics of circular motion. In this exploratory article, we recruit the rope dart as a tool for experiential dialogic physics teaching. We first briefly introduce some very basic rope dart tricks. Next, we provide a typical whole-class dialogic discussion about the circular motion of a rope dart. Finally, we analyze this discourse and discuss some possible pedagogical merits of the proposed approach. |
Studying the Physics of the Sling by Automating the Shooting
| Pengarang | : | Masbudi, Mirah S,Gan Shu San |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 96-99 |
| Abstrak | : | The sling is a tool that has accompanied humanity since prehistoric times. It consists of a rope with a handle at one end and a cradle in the middle for a stone, clay, or metal projectile. It is used in hunting and herding, and it was of great importance in ancient wars, since a skilled slinger can reach targets more than 100?m away. The majority of works on the topic are of an archaeological nature, probably due to the complexity of modeling the process of shooting. In this work, we present a systematic study comparing manual and automated shooting to understand the physics of this amazing tool with the goal of being easily replicated and expanded by physics students. |
Visualizing Electric Fields Using Rubbed Balloons as the High-Voltage Source
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 93-95 |
| Abstrak | : | Developing a conceptual understanding of electrostatic interactions, electric fields, and Coulomb’s law is very important in undergraduate physics courses, and visualizing the electric field produced by charged electrodes offers a unique opportunity for students to initiate a basic understanding of electromagnetism. The experiment of visualizing electric field lines using seeds immersed in oil is typically used at universities as a lecture demonstration that needs big electrostatic machines to generate the necessary electric fields. Here, we present a simple experimental setup for the visualization of electric field lines that could be used at a massive scale in schools and universities. Our setup uses short filaments of paintbrush hairs immersed in sunflower cooking oil inside a plastic petri dish, and produces beautiful patterns of electric fields due to charged electrodes. Instead of using high-voltage generators to charge the electrodes, the high voltage is produced by charged balloons resting on isolated metallic pans... |
An Entertaining Resonance Experiment with Just Two Spring Scales
| Pengarang | : | Yoe Kiem San,Kristanto, Philip |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 90-92 |
| Abstrak | : | Resonance is a topic included in most introductory physics courses. Any mechanical system experiences resonance if it is driven by a periodic force with a frequency that matches its natural frequency. There are plenty of simple demonstrations of the resonance phenomena of mechanical systems that can be set up using readily available items.1–5 Here I present a very simple approach to demonstrate the phenomena using just two spring scales. The experiment presented here performs a “frequency sweep” and is also very entertaining to watch. |
Using 19th-Century Physics to Discover Einstein’s Most Famous Equation
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 87-89 |
| Abstrak | : | I had some very bright AP physics classes during my 35 years as a high school physics teacher. Because those students had already completed my PSSC-style first-year class, I was able to help them discover the basics of electricity and magnetism by using lab experiments and Socratic questioning. (My complete class worksheets can be downloaded from the URL in Ref. 1.) For classes with the ability to master the basics, I chose to have my students make a simple discovery that does not appear in their textbooks. I sent a carefully selected volunteer2 to the blackboard to solve the following problem with the help of classmates: Imagine a radio wave passing through a vacuum. Imagine a small region at the crest of that wave, small enough so that the electric and magnetic fields within it are nearly uniform. |
Free-Point Friday: An Intervention Model for Introductory Physics
| Pengarang | : | Nathan D. Davis |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 84-86 |
| Abstrak | : | Often, assessments in undergraduate physics courses are summative. Instructors impose time constraints on the students, and students are not given opportunities to apply any feedback to then work to build their understanding of the material.1,2 In this paper, we describe a modest supplemental instruction-style intervention that turned weekly, summative content quizzes into opportunities for formative assessment. This was a graduate-student-led effort in an algebra-based introductory physics course at Auburn University. Though we did not have a randomized control group, we used regression analysis to show that students who attended the supplemental intervention, called Free-Point Friday (FPF), performed better than peers with equivalent physics diagnostic scores, self-efficacy, and mindset at the beginning of the semester. |