Center of mass (CM) is an important concept in physics, especially when studying extended bodies. For example, general motion of an extended body can be considered as the sum of the translational motion of the CM plus other types of motion about that CM. CM also can be regarded as a "balance point" so that a system supported at its CM…

Barlow's wheel has been a favorite demonstration since its invention by Peter Barlow (1776-1862) in 1822. In the form shown in Fig. 1, it represents the first electric motor. The interaction between the electric current passing from the axle of the wheel to the rim and the magnetic field produced by the U-magnet produces a torque that turns…

We have developed an eye-catching demonstration that showcases a variety of physics topics from total internal reflection to electrostatics to non-Newtonian fluid dynamics, including the Kaye effect. The essential components of the demonstration include a vertical stream of liquid soap in which a laser pointer is internally reflected, and which…

It has been the author's experience over many years, no doubt shared by others, that a stick of chalk usually breaks into three pieces when accidentally dropped onto the floor. I rarely gave it any thought, apart from noting that the fundamental mode of vibration of a freely supported, rigid rod has two nodes at an equal distance from each…

The classical demonstration experiment on acoustic beats using two signal generators and a dual trace oscilloscope is an important ingredient in teaching the subject. This short laboratory note aims to point out what may be the simplest demonstrative experiment on acoustic beats to carry out in a classroom without employing any lab apparatus.

The 1884 book "Flatland: A Romance of Many Dimensions," written by Edwin Abbott, has captured the interest of numerous generations, and has also been used in schools to help students learn and think about the concept of dimension in a creative, fun way. In 2007, a film was released called "Flatland: The Movie," and over one…

A science video blog, which has gone viral, shows a wooden block shot by a vertically aimed rifle. The video shows that the block hit dead center goes exactly as high as the one shot off-center. (Fig. 1). The puzzle is that the block shot off-center carries rotational kinetic energy in addition to the gravitational potential energy. This leads a…

During the last few years teaching physics, I have noticed that my students are becoming more and more interested in the topic of radiation. Mobile phones, modern game consoles, and WiFi--all of these devices involving some kind of radiation are part of our students' everyday lives. Students are also frequently confronted in the media with…

Helping students develop an understanding of how to interpret experimental data trends is an important part of the introductory physics laboratory. Unfortunately, many of my colleagues have lamented that too many of their students do this poorly. This is a common refrain, and past research has already revealed student difficulties with…

This is not a treatise on optics or the index of refraction. It is merely a demonstration that will surprise and engage many of your students. We have all put a pencil in a beaker of water and observed how it appears to bend. Not so much fun or engaging, is it? Why not illustrate this optical effect by taking your students spearfishing?…

Maxwell's discovery of the relation between electricity, magnetism, and light was one of the most important ones in physics. With his added displacement current term, Maxwell showed that the equations of electricity and magnetism produced a radiation solution, electromagnetic (EM) radiation, that traveled with a speed of c=1/v(e0µ0). The…

In this article we propose an activity aimed at introductory students to help them understand the Stefan-Boltzmann and Wien's displacement laws. It only requires simple materials that are available at any school: an incandescent lamp, a variable dc energy supply, and a computer to run an interactive simulation of the blackbody spectrum.…

Many students have owned or seen fluids toys in which two immiscible fluids within a closed container can be tilted to generate waves. These types of inexpensive and readily available toys are fun to play with, but they are also useful for provoking student learning about fluid properties or complex fluid behavior, including drop formation and…

As is true of a far more famous story, it all began a long time ago, in a galaxy far, far away. It even involved a binary star system. A small star, called a white dwarf, had become a burned out husk of its former self and it turned to gorging on hydrogen and helium from its bloated red giant neighbor. The transferred gas reignited the fires of…

Stability is often an important consideration in both static and dynamic systems. While introductory students soon grasp the balance of forces required for constant velocity motion, it generally takes longer for them to reliably identify the various torques involved in producing rotational equilibrium. Accelerating systems have the additional…