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| Relative Density of a Substance |
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In order to determine the density of a substance or an object, we find out the mass and volume of the substance and use the relation  . This is possible only if the object has a regular shape. |
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| It is difficult to measure the dimensions an object with irregular shape. In such cases we express the density of the object in comparison with that of water. |
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| The relative density of a substance is the ratio of the density of the substance to the density of water at 4oC. We take the relative density of water as one. |
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| What is meant by the statement relative density of gold is 19.3? |
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| It means that gold is 19.3 times denser than an equal volume of water. Those objects whose relative density is less than one will float in water and those greater than one will sink. |
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| Now, if we take equal volumes of the substance and of water, then the above becomes, |
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| As the relative density is a ratio of two similar quantities it has no unit. |
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