The Zimbabwe Secondary School Science Project (ZIM-SCI) developed student study guides, corresponding teaching guides, and science kits for a low-cost science course which could be taught during the first 2 years of secondary school without the aid of qualified teachers and conventional laboratories. This ZIM-SCI study guide presents activities and experiments for a three-part unit in which students investigate various aspects of force. Part 1 focuses on: familiar forces and the changes they cause; magnitude and direction of force; opposing and balancing forces; unbalanced forces (leading to the concept of acceleration); momentum; magnetic and electrostatic forces; and gravity. Part 2 focuses on measurement of forces; instruments used to measure forces; and friction. Part 3 concentrates on the concept of work, leading to definitions for work and for joule as the unit of energy. Machines are introduced as devices which make work "easier," laying the foundation for introducing the concept of "power" and definition of a Watt. A simple experiment measuring muscle power and a comparison of power available from various common energy converters concludes the unit. Information is provided throughout the unit to help students understand the scientific concepts behind the activities and experiments. (JN)