PRISM Magazine On-Line  -  January 2000
Teaching Toolbox
Metrics Made Easy

By Ray Bert

When NASA's $125 million Mars Climate Orbiter broke up in the Martian atmosphere last fall, the loss seemed to underscore the tenuous nature of exploring even our relatively close neighbors in the solar system—and how fragile cutting-edge technology can be.

But when a review board investigating the craft's demise concluded that the Orbiter had flown too close to the Martian surface because scientists failed to convert critical data from one measurement system to another, the incident served to spotlight something else: the failure to fully embrace the metric system in the United States, even among elite engineering and science organizations.

Metric advocates often argue that, like learning a new language, becoming comfortable with a new system of measurement is best accomplished with immersion techniques, and at a young age. But what about engineering students who are indoctrinated in the U.S system of pounds, inches, and gallons? Ian N. Robertson, a professor of civil engineering at the University of Hawaii at Manoa, has some suggestions that can help.

Noting that introducing students to the metric system through numerical conversions is confusing and difficult for students to retain, Robertson recommends using easily visualized common objects to teach them to think in metric. Here are some of his rough equivalents:

  • 1 packet of sugar substitute: 1g (gram)
  • 1 small apple: 1N (Newton)
  • 1 football running back: 1kN (kiloNewton)
  • 1 card table: 1m2 (meter squared)
  • 1 squared toothpick end: 1mm2 (millimeter squared)

To help students visualize a more abstract concept like one pascal (1 Pa or 1 N/m2) of pressure, have them imagine apple sauce made from a single apple spread thinly enough to cover the card table. Clearly this is an extremely small pressure, and of little use in most engineering situations.

Similarly, they can experience a force of approximately one megapascal (1 MPa or 1 N/mm2) by sticking a toothpick into one of the apples and balancing the other end of the toothpick on their finger.

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