A combination of a winch and a block and tackle pulley system demonstrates the power of the wheel and axle when combined with multiple pulleys. This system can demonstrate the energy saving ability of complex machines. The science project is completed in two steps. Students connect a light rope to a 2 1/2-lb. weight, and then tie the other end of the rope to a spring scale. The first step is completed by lifting the 2 1/2-lb. weight and showing the actual weight of the object. The second step of the project is completed by passing the rope through a block and tackle pulley, and then tying the other end of the rope to the barrel of a winch. The spring scale is attached to the handle on the winch. The student turns the crank handle and measures the force required to lift the weight via the machine. The force required to lift the 2 1/2-lb. weight by the winch, which is shown by the spring scale, will be significantly less than the actual weight of the object.
The power takeoff on a farm tractor is used by farmers to transfer power to farm implements which are towed behind the tractor. The power takeoff, or PTO, is a shaft rotating at low speeds and high torque. The farmer connects this shaft to a transmission on implements towed behind the tractor such as the harvester, combine, hay baler or seed planter. An excellent project for eighth grade students involves researching the PTO and writing a report that describes how many simple machines they can identify in the complex machinery towed behind a tractor that is connected to the PTO shaft.
Most elementary age children are familiar with the Lego building block toys. Lego building blocks now include more pieces than square and rectangular blocks. Lego toys and the advanced line of the Technic kits feature wheels and axles, pulleys and levers, battery-powered and even some remote controlled motors. An entertaining science project for eighth graders can be constructed from the Lego and the interchangeable Technic building blocks. Instruct students to build a machine roughly the size of a breakfast cereal box, The machine must carry an average size marble from the lower left corner of the machine to the upper right corner. Students will have to use levers, wheels, axles and pulleys to facilitate the marble's movement.
The medieval trebuchet was the Cadillac of long-range offensive weaponry in medieval Europe. By combining a number of simple machines, a traditional catapult was improved upon. The trebuchet could throw more weight farther and faster than a catapult. The machine was also easier to load and reload because of the advanced design. Ask students to construct a model trebuchet and then write a report identifying the individual simple machines used to create this complex device.