Object A is in circular motion relative to object B if object B is in circular motion relative to object A. A way of visualizing the relative circular motion of two objects is presented with a simple procedure for a classroom demonstration. (Contains 7 figures.)

Children's understanding of density is riddled with misconceptions--or so it seems. Yet even preschoolers at times appear to understand density. This article seeks to reconcile these conflicting outcomes by investigating the nature of constraints available in different experimental protocols. Protocols that report misconceptions about density used…

Spherometers are instruments designed to measure the radius of curvature of spherical surfaces. They are particularly useful in situations where only a portion of the spherical surface is available, for example, for measuring the radii of curvature of spherical lenses. A spherometer can be easily modified so that it can also be used to measure the…

Flight fascinates people of all ages. Recent advances in battery technology have extended the capabilities of model airplanes and toy helicopters. For those who have never outgrown a childhood enthusiasm for the wonders of flight, it is possible to buy inexpensive, remotely controlled planes and helicopters. A toy helicopter offers an opportunity…

Principles of direct current have long been recognised in the literature as presenting difficulties for learners. Most of these difficulties have been reported in the context of the traditional electron flow model. In this paper, an alternative approach for high school students using a field model is explored. Findings from a range of short pilot…

The concept of a positive hydrogen entity, later called the hydrogen ion and proton, seems to have started with Theodor von Grotthuss in 1805. The conception proposed by von Grotthuss has evolved via the works of many scientists; especially the contributions of Justus Liebig, Svante Arrhenius, S. P. L. Sorensen, I. M. Kolthoff, and R. P. Bell.…

Participants estimated the imagined elongation of a spring while they were imagining that a load was stretching the spring. This elongation turned out to be a multiplicative function of spring length and load weight--a cognitive law analogous to Hooke's law of elasticity. Participants also estimated the total imagined elongation of springs joined…

Some physicists have pointed out that we do not know what force is. The most common definition of force in textbooks has been criticized for more than two centuries. Many studies have shown that the concept of force is a problem for teaching. How to conceive force on the basis of the concepts and criticism of force in the works of Newton, Euler,…

This paper was first motivated by the following question: "A pair of twins, R and S, each gives the "same" hard push on a block. R's block is on a rougher floor than S's. Who does more work?" It is shown that S will do more work on his block if there is no constraint on the distance over which the force is applied. On the other hand, if the…

The simple task of bouncing a ball on a racket offers a model system for studying how human actors exploit the physics and information of the environment to control their behavior. Previous work shows that people take advantage of a passively stable solution for ball bouncing but can also use perceptual information to actively stabilize bouncing.…

For both casual and avid fans alike, Olympic and other sporting events can provide a wealth of data for simple physics analyses. One of the most impressive performances in recent Olympic history is that of Usain Bolt in the track-and-field sprinting events during the 2008 Summer Games. Over a seven-day span, Bolt set world records in the 100-m and…

Several years ago a student asked why so many things in the solar system were round. He noted that many objects in the solar system, although not all, are round. The standard answer, which he knew, is that the mutual gravitational attraction of the molecules pulls them into the shape that gets them as close to each other as possible: a sphere.…

Fill an ordinary latex balloon with helium gas and you know what to expect. Over the next day or two the volume will decrease noticeably as helium escapes from the balloon. So what happens when a latex balloon is filled with carbon dioxide gas? Surprisingly, carbon dioxide balloons deflate at rates as much as an order of magnitude faster than…

As co-authors of a recent publication in "Physical Review Special Topics-Physics Education Research", we have received inquiries about the publication process. We will describe the process of creating an article based on team work, in our case the work of the Texas Physics Assessment Team. Many physics teachers have opportunities to participate in…

The goal of this work proposed for undergraduate students and teachers is the calibration of a tungsten filament lamp from electric measurements that are both simple and precise, allowing to determine the temperature of tungsten filament as a function of the current intensity. This calibration procedure was first applied to a conventional filament…