Reviews the concepts behind atmospheric optical phenomena such as rainbows and anticrepuscular rays. Describes the experience of observing these two phenomena simultaneously and calculates the probability of that observation. (JRH)

Discusses the Doppler effect for relative motion between a source of waves and an observer and the orbital dynamics of communications satellites. Presents preliminary calculations of the satellite's altitude and linear velocity using only the concepts of the Doppler shift and the mechanics of motion in a circular path. (JRH)

Describes the laws of physics that allow a motorcycle rider to control the flight of a motorcycle over obstacles in a motocross track. (JRH)

Describes the construction of a bed of nails that can be used to illustrate the relationship between force and pressure. (JRH)

Presents experiments that use Helmholtz resonators and have been designed for a sophomore-level course in oscillations and waves. Discusses the theory of the Helmholtz resonator and resonance curves. (JRH)

Discusses the reasoning behind the determination of the distance from Earth to the Moon by the Greek philosopher Aristarchus upon observing a lunar eclipse. Presents calculations for estimating Earth's distance from the Moon using simple observations made during a solar eclipse. (JRH)

Reports that environmental radioactivity levels vary with temperature and precipitation and these effects are due to radon. Discusses the measurement of this environmental radioactivity and the theory behind it. (JRH)

Presents an activity designed for introductory physics courses that enhances students' understanding of the concept of waves, especially the superposition of waves. Uses two different approaches that end with the same result and enable students to see the connection between spatial and temporal properties of waves and their superposition. (JRH)

Describes the construction and use of a nondriven pendulum that can be used in a classroom to demonstrate the rotation of Earth on its axis. (JRH)

Describes the design and working of inexpensive accelerometers that can be moved by hand on an overhead projector and give an observable indication when their acceleration equals or exceeds a certain value. (JRH)

Describes the physics behind the shadows cast on a stream bed by subtle dimples on the surface of transparent water. (JRH)

Discusses the difficulties with the standard model for introduction of attractive forces into the van der Waals equation. Presents an analysis in terms of force and time delays and an alternative analysis for more advanced students in terms of energy. (JRH)

Presents a demonstration that uses insulated conductors and hairs clipped from rabbit fur to help students visualize the electric field in three dimensions and motivate them to try their own variations. (JRH)

Presents an experiment that uses the measurements of the impulse required to stop a moving mass by three different methods to demonstrate that regardless of whether the maximum force is large or small, approximately the same impulse is required. (JRH)

Describes an introductory physics course at the University of the Western Cape that shifted its fundamental approach from a mathematical focus to a conceptual focus based on verbal and written articulation of understanding. Reports that this approach enhanced student understanding of introductory physics. Contains 21 references. (JRH)