Density is a physical property defined as the ratio of a substance's mass to its volume. It is an intensive property, so it does not depend on the size of the sample and can therefore be used to help identify a substance. For instance, lead has a much higher density than water, which is why it sinks.

密度是一种物理性质,定义为物质的质量与体积之比。它是强度性质,不随样品大小而变化,因此可用于帮助鉴别物质。例如,铅的密度远大于水,所以铅会下沉。