This lesson is the second of a four-part unit for Grades 5-8 on the key forces in flight: lift, weight, thrust, and drag. Weight is the measure of the gravitational force that pulls the airplane back to earth. The force of lift must be greater than the weight of the aircraft to enable it to climb. The lesson helps students understand the difference between mass and weight as they investigate wing design and factors that produce lift. The lesson includes objectives, warm-up questions, background information for teachers, assessment questions, classroom activity, and web-based reference material. TeachEngineering is a Pathway project of the National Science Digital Library. It provides a large collection of teacher-tested, research-based content for K-12 teachers to connect real-world experiences with curricular content.