Measurement
How far is it from here to there? How much does your television weigh? If we did not measure things, everything we build would fall right down. In this lesson, we will explore how a standard system of measurement helps us understand the entire world.
Whose Foot is a Foot?
Because everyone has different sized feet! If a builder asked for a piece of wood that was three feet long, the actual size of the wood would change depending on who was doing the measuring. Nobody could agree on how long a foot actually was.
They created a standard. A king stepped in and declared that his "royal foot" would be the standard measurement for the entire land. Every other ruler or measuring tool had to be fitted against his foot so that everyone was finally using the exact same measurement.
Put Your Instincts to the Test
Think about what you already know about the metric system. Pick an answer for each question, then see if your instincts were right.
Because humans have ten fingers! Bill Nye the Science Guy explains that since early humans used their hands to count, a base-ten system was the most natural way to organise mathematics. It makes scaling up from millimetres to kilometres incredibly easy.
Exactly one kilogramme. This is the brilliant secret of the metric system. A volume of 1,000 cubic centimetres perfectly holds one litre of water, and one litre of water has a mass of exactly one kilogramme. Everything connects!
He used the freezing and boiling points of water. He set the exact temperature at which water turns to ice as zero, and the temperature at which water boils as one hundred. This simple hundred-degree standard is now used all over the world.
Understanding the Science
Tap each card to reveal the fascinating mechanics behind our universal system of measurement.
Key Concepts
Standard Measurement
Tap to learn moreWe measure things all the time to compare one object to another. If we did not use a standard system, nothing we build would ever fit together. Bill Nye the Science Guy explains that a bulb made in Baltimore screws perfectly into a socket in Seattle because both factories use the exact same standard measurements. A universal standard ensures that human engineering works seamlessly around the globe.
The Metre
Tap to learn moreHumans are roughly a specific size, so we always wanted a unit of measurement that was about the length of a long stride. To make this standard universal, early scientists looked at the Earth. They took the physical distance from the North Pole down to the Equator and divided it by exactly ten million. That specific fraction became the original metre, the foundational unit of length for the metric system.
Measuring Area
Tap to learn moreIf you want to know how much flat space an object covers, you need to measure its area. You do this by taking the length of the object and multiplying it by the width. Bill Nye the Science Guy demonstrates this with wooden boards. If a board is one metre long and one metre wide, it covers exactly one square metre of space. Area tells us how much flat room something takes up.
Measuring Volume
Tap to learn moreWhile area measures flat surfaces, volume measures how much three-dimensional room an object takes up. To find volume, you multiply length by width by height. If you have a solid cube that measures exactly one metre on all three sides, it represents one cubic metre of volume. Volume is crucial for figuring out how much empty space exists inside containers.
Litres and Kilograms
Tap to learn moreThe metric system originally linked length, volume, and mass together using pure water. If you build a cube that is one-tenth of a metre wide on all sides, the volume inside is exactly one litre. If you fill that one litre of volume with fresh, cold water, it will weigh exactly one kilogram. This beautiful connection allowed early scientists to convert between physical space and physical mass.
The Celsius Scale
Tap to learn moreA thermometer uses a liquid metal that predictably expands when it gets warm and contracts when it cools down. The astronomer Anders Celsius created a standard Celsius scale by testing this liquid in water. He marked zero exactly where water freezes into ice, and marked one hundred exactly where water boils. There are exactly one hundred degrees between freezing and boiling.
Measuring Time
Tap to learn moreWe measure time to record history and keep society on a schedule. The Earth itself acts as a giant clock. One complete spin of the Earth gives us a day and a night, while one full journey around the sun gives us a year. Humans invented calendars to keep track of these long planetary movements, and we invented clocks to divide the spinning days into precise hours, minutes, and seconds.
The Power of Ten
Tap to learn moreBecause humans have ten fingers, the entire metric system is built on powers of ten. You can take a standard metre and easily scale it up or down. If you divide a metre by one hundred, you get a centimetre. If you divide it by one thousand, you get a millimetre. Multiply it by one thousand, and you have a kilometre. The power of ten makes scientific mathematics incredibly easy.
Try It: The Universal Metric Lab
Grow the water tank to 10 cm on every side. How much water is that, and how heavy? Then try it with hot water.
In 1795 the kilogram was defined as the mass of one litre of cold water. Water swells as it warms, so a litre of hot water weighs less; the kilogram became a metal cylinder in 1889 and, since 2019, a fixed number from physics.
Apply Your Knowledge
Let us see if you can connect what you have learned about standard measurements to their correct definitions.
Match the Concepts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are an engineer helping to build a brand new commercial aeroplane. The engine parts are being manufactured in Japan, the electronics in Germany, and the wings in the United Kingdom. Explain why using a universal standard of measurement is an absolute matter of life and death.
What Has Changed Since This Episode Aired
This episode first aired in 1998. While the basic principles of standard measurement are identical, the way scientists define these standards has drastically modernised. Here are three things we know now.
Updated: No, because the Earth's surface constantly shifts and changes! Bill Nye was explaining the original historical method because it is easy to visualise. However, since 1983, the metre has officially been defined by the speed of light. It is exactly the distance that light travels in a vacuum in 1/299,792,458 of a second.
Updated: Because the density of water changes slightly depending on the temperature (as you saw in the simulation!), the world relied on a physical cylinder of metal locked in a vault in France to define the kilogramme. However, in 2019, physicists brilliantly redefined the kilogramme using an unchanging law of quantum physics called the Planck constant, measured with a hyper-accurate machine called a Kibble balance.
Updated: The Earth's spin actually wobbles slightly due to earthquakes and the friction of the ocean tides. To keep perfect time for GPS satellites and computers, scientists now use Atomic Clocks. These incredible machines measure the exact microwave vibrations of cesium atoms and are so accurate they will not lose a single second in millions of years.
Test Your Understanding
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Results
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Reflection
Look around the room you are currently in. Can you name three different objects that you would measure using three completely different tools? For example, what would you use to measure the width of your desk, the weight of your bag, or the temperature outside?
Episode Discussion
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