This part contains an algebra-based course on Newtonian mechanics at the high-school level, oriented towards astronomy and spaceflight.
It thus omits rigid body mechanics--no torque or moment of inertia--but includes mass measurements in the weightless environment of a space station (with a simple related experiment), synchronous orbits and space trajectories from available Earth to Mars. Teachers using this material may pick and choose parts to fit the time and level of the class.
The stress is on concepts, such as vectors and their applications, mass and inertia, and uses of frames of references, including the sometimes confusing question of centripetal vs. centrifugal.
Applications illustrate the way physics makes nature understandable--why hurricanes swirl counterclockwise (but with draining water in a sink, it's fifty-fifty), why wings of jetliners are swept back, why a bicycle cannot be balanced without moving and how energy serves as a currency paying for physical processes, with heat filling the role of the "soft currency" of nature. Newton's discovery of universal gravitation is explained, and his apple tree makes a cameo appearance.
For earlier web pages, covering Kepler's laws, see Part I of "Stargazers" which discusses astronomy.
For applications of Newtonian mechanics to rocket flight (unit #25), the concept of the ballistic pendulum (#26), Lagrangian points (#34) and gravity-assist maneuvers (#35), see Part IV on spaceflight