Machines and Tools, Part II
In this activity, students gain first-hand experience with the mechanical advantage of pulleys. Students are given the challenge of helping save a whale by moving it from an aquarium back to its natural habitat into the ocean. They set up different pulley systems, compare the theoretical and actual mechanical advantage of each and discuss their recommendations as a class.
Figure 1. The world's largest crane, or an example of a pulley.Copyright U.S. Department of Transportation, Federal Highway Administration, http://www.fhwa.dot.gov/bridge/crane27.htm
Engineers need to know the measured effectiveness of the tools they use. This can be learned through experience or calculated theoretically. A pulley is a simple machine often used in engineering activities and accordingly has a measurable effectiveness, or mechanical advantage. Pulleys are good machines for lifting heavy objects over a direct vertical path. Pulleys are often incorporated into the design of various engineering systems such as the crane, where huge loads are manipulated with a little force supplied by a relatively small motor. Cranes can be seen moving buildings, boats, large animals, and even swimming pools.
After this activity, students should be able to:
- Calculate the mechanical advantage of a pulley.
- Explain why the concept of mechanical advantage is useful for engineers.
- Perform engineering design work in a group.