Specific gravity facts for kids

Specific gravity (often shortened to SG) is a way to compare how heavy a substance is compared to water. It tells us if something will float or sink in water, and how much it will do so.

Think of it like this: if you have a rock and a feather, the rock is much heavier for its size. Specific gravity helps us measure this "heaviness" in a standard way, using water as our reference.

What is Specific Gravity?

Specific gravity is a number that shows the density of a substance compared to the density of water. Density is how much "stuff" (mass) is packed into a certain space (volume).

• If a substance has a specific gravity greater than 1, it means it is heavier than water. So, it will sink.
• If a substance has a specific gravity less than 1, it means it is lighter than water. So, it will float.
• If a substance has a specific gravity of exactly 1, it has the same density as water. It will usually stay suspended in the water.

For example, a piece of wood might have a specific gravity of 0.6. This is less than 1, so it floats. A metal coin might have a specific gravity of 8.0. This is much greater than 1, so it sinks quickly.

How is it Used?

Specific gravity is useful in many areas:

• Science experiments: You can easily tell if an object will float or sink.
• Engineering: Engineers use it to design ships, submarines, and other things that interact with liquids.
• Gemology: Experts use specific gravity to help identify different gemstones.
• Food industry: It helps check the quality of liquids like milk or fruit juice.

Related pages

• Buoyancy
• Fluid mechanics
• Relative density

Images for kids

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  An empty glass pycnometer and stopper

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  A filled pycnometer

See also

In Spanish: Densidad relativa para niños