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…

Our high school optics course finishes with an assignment that students usually appreciate. They must take pictures of everyday situations representing optical phenomena such as reflection, refraction, or dispersion, and post them on Instagram. When the photos were presented to the class, one student revealed an intriguing photo, similar to Fig.…

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…

Recently much attention has been paid to the history of the discovery of Hubble's law--the linear relation between the rate of recession of the remote galaxies and distance to them from Earth. Though historians of cosmology now mention several names associated with this law instead of just one, the motivation of each actor of that remarkable…

Most high school and introductory college physics classes study simple harmonic motion and various wave phenomena. With the majority of states adopting the Next Generation Science Standards and pushing students to explore the scientific process for themselves, there is a growing demand for hands-on inquiry activities that involve and develop more…

By describing the motion of a charged particle in the well-known nonuniform field of a current-carrying long straight wire, a variety of teaching/learning opportunities are described: 1) Brief review of a standard problem; 2) Vector analysis; 3) Dimensionless variables; 4) Coupled differential equations; 5) Numerical solutions.

Planar x-ray imaging is a ubiquitous diagnostic tool and is routinely performed to diagnose conditions as varied as bone fractures and pneumonia. The underlying principle is that the varying attenuation coefficients of air, water, tissue, bone, or metal implants within the body result in non-uniform transmission of x-ray radiation. Through the…

When all parts of an electric circuit are at the same potential, no electric current flows and it is said to be in "equilibrium." Otherwise, a current will flow from the higher potential parts to the lower ones, as when we make contact between the plates of a charged capacitor. The resulting discharging process towards equilibrium is a…

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?…