Uses Newton's laws of motion to describe the theory behind the observation that when bread falls off a table it always lands butter-side down. (JRH)

Discusses descriptions of the way in which an optical system controls the quantity of light that reaches a point on the image plane, a basic feature of optical imaging systems such as cameras, telescopes, and microscopes. (JRH)

Answers a student's question about the emission of a positron from a nucleus. Discusses the problem from the aspects of the uncertainty principle, beta decay, the Fermi Theory, and modern physics. (YP)

Discusses the average speed differences between hydrogen and oxygen molecules contained in a jar. (YP)

Described is the subject of biological scaling for physics teachers including examples and in-depth reading. Topics are elements of scaling, terminal velocities, Lilliputian and Brobdingnagian, brain evolution, dolphin echolocation, surface tension, gravity change, food and oxygen, and seeing. Ten references on physics and size, and ten questions…

Asks the relationship between mass and skidding distance. Provides a problem with illustrations and an answer. (YP)

Discusses the making of a light engine powered by sunlight or a lamp. Describes the materials and construction method with detailed specifications and diagrams. (YP)