Though central to any pedagogical development of physics, the concept of mass is still not well understood. Properly defining mass has proven to be far more daunting than contemporary textbooks would have us believe. And yet today the origin of mass is one of the most aggressively pursued areas of research in all of physics. Much of the excitement…

Discusses the drafting of lines of force and equipotentials in static potential fields, examining the general properties of equipotentials and field lines, diagrams from the literature, and the field of equal charges of opposite sign. Examples used are from both American and European textbooks. (JN)

Discusses topics related to high-energy, gamma-ray astronomy (including cosmic radiation, gamma-ray detectors, high-energy gamma-ray sources, and others). Also considers motivation for the development of this field, the principal results to date, and future prospects. (JN)

Discusses a problem (on page 523 of "College Physics," by Sears, Zemansky, and Young, published by Addison-Wesley, 1980) concerning light bulbs and resistance. Shows why the assumption of constant resistance is unrealistic and provides guidelines for revision. (DH)

Outlines how the radiative properties of a surface can be tailored so as to be favorable for efficient utilization of energy. The radiative properties of concern are transmittance, reflectance, absorptance, and emittance. (JN)

Presents a laboratory exercise designed to introduce graphical extrapolation. Major advantages of the method are in its simplicity and speed. The only measuring devices are a centimeter ruler and a micrometer caliper to check wall thickness. (JN)

Provides a method for correcting the photoemission from a collector when using the photoelectric effect experiment to determine Planck's constant. The problem results from a negative current through the cell and makes the measurement of the cutoff potential difficult. (DH)

Provides procedures for a simple laboratory activity on exponential growth and its characteristic doubling time. The equipment needed consists of a large plastic bucket, an eyedropper, a stopwatch, an assortment of containers and graduated cylinders, and a supply of water. (JN)

Misconceptions occur because the caliper is often read with the same significant figures as a meter stick; however, the precision of the vernier caliper is greater than the precision of a meter stick. Clarification of scale reading, precision of both tools, and significant figures are discussed. (JN)

Discusses refraction in terms of the deviation of light. Points out that in physics courses where very little mathematics is used, it might be more suitable to describe refraction entirely in terms of the deviation, rather than by introducing Snell's law. (DH)

A relatively simple opto-electronic setup is described that utilizes a cadmium sulphide (CdS) photoconductive cell to detect resonance of a stretched vibrating string or wire. The display may be either an oscilloscope or a frequency counter. Also describes an inexpensive socket for flanged-base light bulbs. (JN)

Presents calculations after discussing exponential growth that deal with the determination of the time of exhaustion at different rates of consumption. (PR)

Describes the design and use of a projectile motion apparatus to illustrate a variety of projective motion results typically discussed in an introductory course. They include independence of horizontal (constant speed) and vertical (constant acceleration) motions, parabolic path shape, and other types of motion. (JN)

Presents an alternative method for measuring the electronic charge using data from the electrolysis of acidified distilled water. The process (carried out in a commercially available electrolytic cell) has the advantage of short completion time so that students can determine electron charge and mass in one laboratory period. (DH)

Explains the physical principles which result in various colors of the sky. Topics addressed include: blueness, mystical properties of water vapor, ozone, fluctuation theory of scattering, variation of purity and brightness, and red sunsets and sunrises. (DH)