This Topic in Depth explores the Web's offerings on the physics of sailing. The first site by Joe Wolfe of the School of Physics at the University of New South Wales is entitled The Physics of Sailing (1). Here, visitors will learn how boats can sail upwind, how they sail faster than the wind, and why large boats never sail directly with the wind. The one-page site offers simple descriptions, good illustrations, and some basic calculations that correspond with the physics. The second site is an interactive online sailing simulation (2) presented by NationalGeographic.com. This very addicting activity lets users adjust the sail and rudder direction of the boat to see how fast it will go in various directions. It also explains the various positions of the boat and the best tactics to maximize speed. The next page is from the DynaWing Company Web site called Why Wing Sails? (3). The page explains why wing sails have a better lift-to-drag ratio than traditional sails and illustrates airflow, foils, the venturi effect, and more. The American Model Yachting Association maintains the next site titled Basic Sail Theory and Concepts (4). The site describes the physics of the sail and the centerboard of a boat, which projects downward into the water. Visitors of the site will also learn about the three forms of wind that affect a boat (apparent, true, and induced) and even some basic sailing terms. The fifth site is an article from NASA about the possibility of using sails to propel spacecraft called Sailing to the Stars (5). The August 2000 article reports how NASA scientists believe a "spacecraft could deploy 'sails' and be propelled through our solar system using the pressure of photons (light) from the Sun." The next site is from WB-Sails called The Quest for the Perfect Shape (6), which explores how the shape of sails effect a boat's performance. The page describes the heeling force of wind, the design wind, and the parts of a sail, and even has a link to a sail power calculator. From ESPN comes a physics lesson plan called Sailing Through Bernoulli (7). The lesson plan teaches kids about the Bernoulli principle, which explains how wings produce lift. One of the activities suggests students hold one hand out the window of a moving car and as they change the angle of their hand they can experience a lift force on their hand. The last site is maintained by the Massachusetts Institute of Technology Aerodynamics and Astronomics Department called How a Sailboat Sails into the Wind (8). The site tells a bit of the history of sails from the first square sails dated 3000 BC to the present designs. Other things of interest include explanations of several equations and forces related to sailing.