Home » Physics » Introductory skills » Metric mania

Metric mania

What are we learning?

• The difference between the metric  and English (Imperial) systems of measurement.

Why are we learning this?

• The metric system is used in all Western and industrial nations.

• Products sold in the USA are increasingly labeled with metric units.

• Every year more factories and repair shops use more metric tools.

Craftsman Metric tool set Sears

Part 1

Based on background knowledge, answer:

1. Why do Americans often use the English (“Imperial”) system instead of the metric system?

2. Why did the rest of the world change to the metric system?

3. When would someone need to convert a metric to an English measurement?

4. What could go wrong if someone makes a mistake when converting from metric to English?

Simpsons car accident

Part 2: Read these examples

1. The Gimli Glider


The Gimli Glider is the nickname of an Air Canada aircraft that was involved in an unusual aviation incident. On July 23, 1983, Air Canada Flight 143, a Boeing 767–233 wide body jetliner, ran out of fuel at an altitude of 12,500 metres (41,000 ft) above mean sea level, about halfway through its Montreal to Edmonton flight.

How could they have run out of fuel halfway through their flight?!?!

Fortunately, the flight crew was able to glide the aircraft safely to an emergency landing on an auto racing track that was previously a Royal Canadian Air Force base in Gimli, Manitoba.

The subsequent investigation revealed a combination of company failures and a chain of human errors that defeated built-in safeguards. The amount of fuel that had been loaded was miscalculated because of a confusion as to the calculation of the weight of fuel using the metric system, which had recently replaced the English (imperial) system for use with the 767.


2. Mars Climate Orbiter

Mars Climate Orbiter metric

The $125 million satellite was supposed to be the first weather observer on another world. But as it approached the red planet to slip into a stable orbit Sept. 23, the orbiter vanished. Scientists realized quickly it was gone for good.

“It was pretty clear that morning, within half-an-hour, that the spacecraft had more or less hit the top of the atmosphere and burned up,” recalled NASA engineer Richard Cook, who was project manager for Mars exploration projects at the time.

A NASA review board found that the problem was in the software controlling the orbiter’s thrusters. The software calculated the force the thrusters needed to exert in pounds of force. A separate piece of software took in the data assuming it was in the metric unit: newtons. “The units thing has become the lore, the example in every kid’s textbook from that point on,” Cook said. “Everyone was amazed we didn’t catch it.”

Ultimately, the Mars Climate Orbiter came within 37 miles of the Martian surface. Simulations showed that, at any altitude lower than 53 miles, atmospheric friction would tear the fragile craft apart.

The whole thing could be written off as a miscommunication. Propulsion engineers, like those at Lockheed Martin who built the craft, typically express force in pounds, but it was standard practice to convert to newtons for space missions. One pound of force is about 4.45 newtons. Engineers at NASA’s Jet Propulsion Lab assumed the conversion had been made, and didn’t check.

_ excerpted from “Metric math mistake muffed mars mission”, Wired magazine, Lisa Grossman


3. The Vasa sinks, 1628

What caused the sinking of the Vasa warship in 1628? Again, people who didn’t do a proper conversion between measurement systems.

Vasa stern ship

Vasa set sail on her maiden voyage on August 10, 1628. At the time, she was the most powerfully armed warship in the world, with 64 bronze cannons. Twenty minutes into her journey, the ship was hit by two strong winds. It heeled to port, water gushed in, and the ship sank less than a mile into the journey. Thirty people died.

Soon after, there was an inquest that concluded that the ship had been unstable. But the reasons behind the instability have remained a point of debate over the centuries.

Fred Hocker, an archaeologist at the Vasa Museum, has been trying to find some definitive answers. “We have, over the last three years, measured every single piece of the wood in the ship,” says Hocker. “If we want to understand how the ship was built, that’s what it takes.”

Hocker’s meticulous measurements gave him fresh insight into what made the Vasa unstable. For one thing, the ship was asymmetrical, more so than most ships. “There is more ship structure on the port side of the hull than on the starboard side,” explains Hocker.
“Unballasted, the ship would probably heel to port.”

No wonder the ship tipped to the port side when the winds hit. But why was the ship so lopsided? While examining the ship, Hocker discovered four rulers the workmen had used. Those rulers were based on different standards of measurement at the time!

Two were in Swedish feet, which were divided into twelve inches.

The other two were in Amsterdam feet, which had eleven inches in a foot.

So each carpenter had used his own system of measurement!  “When somebody tells him, make that thing four inches thick, his four inches is not going to be the same as the next guy’s four inches,” says Hocker. “And you can see those variations in the timbers, as well.”


Summary questions

Speculate: (A) What items in your car, school, phone or home might have been designed with metric measurements, and built with metric sized tools?
(B) In what jobs today might you be expected to use metric tools?


We don’t need to make things complicated

Just consider the irony 😉

Metric system funny meme

Why didn’t we change to the Metric system, like the rest of the world? One may speculate, but Grandpa Simpson offers a common response:

Simpsons Metric system is the tool of the Devil

Learning Standards

Massachusetts Science and Technology/Engineering Curriculum Framework
Science and Engineering Practices: 5. Using Mathematics and Computational Thinking:
Apply ratios, rates, percentages, and unit conversions in the context of complicated measurement problems involving quantities with derived or compound units (such as mg/mL, kg/m 3, acre-feet, etc.).

National Council of Teachers of Mathematics
Students need to develop an understanding of metric units and their relationships, as well as fluency in applying the metric system to real-world situations. Because some non-metric units of measure are common in particular contexts, students need to develop familiarity with multiple systems of measure, including metric and customary systems and their relationships.

National Science Teachers Association
The efficiency and effectiveness of the metric system has long been evident to scientists, engineers, and educators. Because the metric system is used in all industrial nations except the United States, it is the position of the National Science Teachers Association that the International System of Units (SI) and its language be incorporated as an integral part of the education of children at all levels of their schooling.

%d bloggers like this: