Physics for ages 12-14  Chemistry for ages 12-13    Roy Wilkinson outlines the background and practical guidelines for teaching these subjects:     6th grade--sound, light, heat, magnetism, electricity  7th grade--6th-grade subjects continued; mechanics, chemistry. Describe the work of factories and transport showing how physics, chemistry, geography, and natural science are interwoven.   8th grade--hydraulics, aeromechanics; practical applications of what has been studied in 6th and 7th grades: meteorology, climatology, chemistry                 Contents:               Introduction  Sound  Light and Color  Heat  Magnetism and Electricity  Mechanics  Hydraulics  Pneumatics  Meteorology and Climatology  Combustion  Salts and Salt-formation  The Metals  The Organic World  The Nature of Substance