Pulleys and inclined planes are two types of simple machines that help to reduce the amount of force, or work, required to complete a task. Pulleys work by reversing the direction of the force applied to move an object. This directional change allows the operator to exert less force than by lifting the object alone. Inclined planes reduce work by increasing the distance the object must travel to reach its destination, but provide a graduated increase in height, thus reducing work.
Explore the fundamental properties and benefits of simple machines by having students construct pulley systems, then measure the amount of force required to lift the same weight to two different levels with and without a pulley. Spring scales help students measure and understand work and how pulleys reduce work. Comparing the effectiveness of pulleys to other simple machines also helps students understand how they work. For instance, students can research and construct examples of the disadvantages of pulleys versus rigid simple machines. Stretching and slipping are two such disadvantages. Students can invent ways to prevent these disadvantages, such as by using chains instead of ropes.
Inclined planes have a variety of different uses, including ramps, chutes, blades, wedges and foils. One inclined plane project involves students finding as many different uses for an inclined plane as possible. Additionally, students can build their own inclined planes out of pieces of Legos, and then use meters to measure the work required to lift the same amount of weight from one height to another with and without an inclined plane. Students can also explore potential and kinetic energy by rolling two differently sized and weighted cans down an inclined plane. Measure the distance the cans roll, then repeat the experiment by pushing the cans down the plane, rather than just releasing them. The cans will roll farther as more energy is applied at the top of the plane.
Projects identifying simple and compound machines explore the significance of these machines in our daily lives. As students explore their homes, yards, school and playground, they identify pulleys and inclined planes in household objects and machinery, such as can openers, truck ramps, scissors and saws. Students can also explore how simple machines such as pulleys and inclined planes work together to form compound machines, reducing larger amounts of work. For instance, students use pieces from the board game mousetrap, including an inclined plane ramp and a pulley to move a marble across the board to trap a plastic mouse.