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Gram

physical science Maturity 11-13 Next article →

A gram is a unit used to measure mass. Mass tells us how much matter is inside an object.

One-yen coin mass
One-yen coin mass

People use grams all over the world every single day. You might see them when you are grocery shopping for food. Many food labels show nutrition facts for every 100 grams of a product. This makes it easy to see the percentage of things like sugar. It is a very helpful way to compare different foods.

Amphetamine
Amphetamine

In cooking, grams are often used for dry ingredients. This helps cooks be very exact with their recipes.

There is a specific way the gram works within a system. It is part of the International System of Units, or SI. In this system, one gram is exactly one thousandth of a kilogram. Scientists use the symbol "g" to write it down. You must put a space between the number and the symbol, like "640 g." You should not use abbreviations like "gm" or "gr." The symbol "gr" actually stands for something else called a grain. Using the right symbol keeps measurements clear for everyone.

Defining a gram has changed over a long time. In 1795, the French National Convention defined it using water. They said one gram was the mass of a tiny cube of pure water. This cube was one cubic centimetre in size. At first, they measured this water at the temperature of melting ice. Later, they changed the temperature to where water is most dense. Density is a measure of how tightly the water is packed. This change kept the definition very close to the original one.

History shows us many different ways to measure mass. The word "gramme" was used in a 1795 decree in France. This replaced an older unit called the gravet. The name comes from a Greek word meaning "letter." Long ago, around 400 AD, a gram was a small part of an ounce. In the 19th century, the gram was a base unit in the CGS system. This stood for centimetre, gram, and second. Later, the kilogram became the main base unit in 1960.

It can be hard to picture how heavy a gram is. You can use everyday objects to help you imagine it. One gram is about the mass of a small paper clip.

Wellcome Foundation Object Wellcome L0044963
Wellcome Foundation Object Wellcome L0044963

A Japanese 1 yen coin also has a mass of exactly 1 gram. This is lighter than a United States penny, which is 2.5 grams. It is also lighter than a British penny at 3.56 grams. A Euro cent weighs about 2.30 grams. Even an Australian 5 cent coin is heavier at 2.8 grams. These small items help us feel the weight of a single gram.

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File:Wellcome Foundation Object Wellcome L0044963.jpg
Wellcome Foundation Object Wellcome L0044963.jpg
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