The density of a material is defined as its mass divided by its volume. The bulk density of powdered and granular materials is often measured by the "tap" density method. A material's tap density is obtained by filling a container of known volume with a known mass of sample and vibrating it. This value is commonly referred to as "tap" density because it is typically obtained using a mechanical device that alternately lifts and drops the container a specified number of times, producing a loud tapping noise.
Because this measurement varies depending on the vigor and number of taps, tap density is not an inherent property of a material. It is nevertheless a measurement of considerable interest in packaging, handling, and shipping bulk granular products.
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