Unit of length facts for kids
A unit of length is a special way we measure how long something is or how far away one thing is from another. Think of it like using a ruler or a tape measure! Different units help us measure everything from tiny hairs to the huge distances between stars.
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Measuring Length: What Are Units?
When we talk about length, we need a standard way to measure it so everyone understands. That's where units of length come in. They give us a common language for size and distance.
The Metric System: SI Units
The most common way to measure length around the world is using the International System of Units (SI). This system is also known as the metric system. It's super easy to use because it's based on tens!
Common Metric Units
- The metre is the basic unit of length in the metric system. It's about the length of a big step or a guitar.
- A centimetre is much smaller, with 100 centimetres making up one metre. It's about the width of your finger.
- A kilometre is much larger, with 1,000 metres in one kilometre. You would measure the distance between towns in kilometres.
Sometimes, you might hear about other metric units that are not part of the main SI system, but they are still based on metres:
- The micron is another name for a micrometre. It's incredibly tiny, one-millionth of a metre! You would need a microscope to see things measured in microns.
- The Norwegian/Swedish mil is a special unit used in those countries. It's equal to 10,000 metres, which is 10 kilometres.
Imperial and US Customary Units
While most of the world uses the metric system, some countries, like the United States, still use Imperial or U.S. customary units. These units are older but are still used every day.
Everyday Imperial Measurements
- An inch is a small unit, about the length of your thumb from the knuckle. There are 25.4 millimetres in one inch.
- A foot is made up of 12 inches. It's about the length of a grown-up's foot. One foot is equal to 0.3048 metres.
- A yard is slightly less than a metre. It has 3 feet or 36 inches. One yard is 0.9144 metres.
- A mile is a much longer unit, used for measuring distances like how far you drive. One mile is about 1,609 metres.
Special Units for Specific Jobs
Some jobs or activities use their own special units of length. These units are perfect for what they need to measure!
Measuring at Sea
Sailors and people who work on boats use these units:
- A fathom is used to measure the depth of water. One fathom is about 1.8288 metres, or roughly the length of a person's outstretched arms.
- A nautical mile is used for measuring distances at sea. It's a bit longer than a regular mile, about 1,852 metres.
Surveying Land
People who measure land, called surveyors, sometimes use older units in the United States:
Horse Racing Distances
In horse racing, they use a special unit:
- A furlong is used to measure the length of a race track. It's about 201 metres.
Measuring Vast Distances in Space
When we look at the stars and planets, the distances are so huge that we need very big units to measure them!
How Astronomers Measure Space
- An astronomical unit (AU) is the average distance from the Earth to the Sun. It's about 149 million kilometres!
- A light year (ly) is the distance light travels in one whole year. Light is super fast, so a light year is an incredibly long distance, about 9.46 trillion kilometres!
- A parsec (pc) is an even bigger unit, used for measuring distances to stars and galaxies. One parsec is about 30.8 trillion kilometres. You might also hear about kiloparsecs (thousands of parsecs) or megaparsecs (millions of parsecs) for truly enormous distances.
Old Ways to Measure Length
Before we had standard rulers and measuring tapes, people used parts of their bodies or everyday objects to measure things. These are called old or historical units.
Historical Units of Length
- A cubit was an ancient unit, usually the length from a person's elbow to the tip of their middle finger.
- A league was a unit of distance that a person or horse could travel in about an hour. Its exact length varied, but it was usually a few miles.
- A pace was the distance of one step. In Ancient Rome, a "double pace" was used, which was about 5 feet.
Using Everyday Things to Measure
Sometimes, in everyday talk, people describe lengths by comparing them to things everyone knows. This helps give a quick idea of size without being super precise.
Fun Ways to Estimate Length
- A Football field is often used to describe a long distance. A typical football field is about 110 metres long.
- The width of a human hair is used to describe something very, very thin. A human hair is usually around 80 micrometres wide.
Images for kids
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A ruler, showing two common units of length: the centimetre and the inch.
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An old way of determining a "rod" unit, using the length of the left foot of 16 randomly chosen people.
See also
In Spanish: Unidad de longitud para niños
