When a cord is run over a pulley, the direction of the applied force is changed. This is a very useful principle in many different machines and a basic principle that shows up again and again in physics classes. Handcrafted from replenishable and durable rubberwood, an eco-friendly sustainable and high-quality hardwood. Includes a teacher guide detailed the history of the model, practical applications and classroom experiments. Measures 10cm W x 17cm L x 42cm H (4"W x 6-3/4"L x 16-1/2"H). Grades 2+. Ages 7+.