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…

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.

To familiarize first-year students with the important ingredients of a physics experiment, we offer them a project close to their daily life: measuring the effect of air resistance on a bicycle. Experiments are done with a bicycle freewheeling on a downhill slope. The data are compared with equations of motions corresponding to different models…

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…

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…

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…

In 1974, Professor Eric Laithwaite demonstrated an unusually heavy gyroscope at a Royal Institution lecture in London. The demonstration was televised and can be viewed on YouTube. A recent version of the same experiment, together with partial explanations, attracted two million YouTube views in the first few months. In both cases, the gyroscope…

The classic experiment to measure the drag coefficient involves dropping coffee filters. Wouldn't it be more fun to try something different? In fact, an experiment on the drag force is conducted nearly 4000 times a day during the baseball season and you have free access to this PITCHf/x data!

A challenge: Can you create a stable top from a single paper clip? Several interesting solutions to this problem were provided by Takao Sakai from Japan, the requirement of each being that the center of gravity be located on the vertical y-axis at the center of the top. In the simplest configuration, we see that there exists a single angle ?…

LEDs, or light-emitting diodes, are cheap, easy to purchase, and thus commonly used in physics instruction as indicators of electric current or as sources of light (Fig. 1). In our opinion LEDs represent a unique piece of equipment that can be used to collect experimental evidence, and construct and test new ideas in almost every unit of a general…

It has been illustrated several times how the built-in acceleration sensors of smartphones can be used gainfully for quantitative experiments in school and university settings (see the overview in Ref. 1 ). The physical issues in that case are manifold and apply, for example, to free fall, radial acceleration, several pendula, or the exploitation…

The damped oscillator is discussed in every high school textbook or introductory physics course, and a large number of papers are devoted to it in physics didactics journals. Papers typically focus on kinematic and dynamic aspects and less often on energy. Among the latter, some are devoted to the peculiar decreasing behavior of energy…

Although we experience motion simply as displacement, we study it through complicated concepts such as acceleration, force, and mass, departing from our everyday experience. But it looks like we can stay attached to our primordial notions of time and length without appealing to any other concepts and still have interesting results.

Gyroscopes are frequently used in physics lecture demonstrations and in laboratory activities to teach students about rotational dynamics, namely, angular momentum and torque. Use of these powerful concepts makes it difficult for students to fully comprehend the mechanism that keeps the gyroscope from falling under the force of gravity. The…