Medical research

Novel model predicts COVID-19 outbreak two weeks ahead of time

People's social behavior, reflected in their mobility data, is providing scientists with a way to forecast the spread of COVID-19 nationwide at the county level. Researchers from Florida Atlantic University's College of Engineering ...

Medical research

Using mice to explore the prevention of blocked arteries

It's long been known that a high-fat diet can lead to clogged arteries, but we have only recently begun to learn in detail how the process works. A new study in experimental mice could go a long way to finding treatments ...

Overweight & Obesity

Built environments don't play expected role in weight gain

People don't gain or lose weight because they live near a fast-food restaurant or supermarket, according to a new study led by the University of Washington. And, living in a more "walkable," dense neighborhood likely only ...

Medical research

Cholesterol levels sustainably lowered using base editing

Base editing is a novel gene editing approach that can precisely change individual building blocks in a DNA sequence. By installing such a point mutation in a specific gene, an international research team led by the University ...

Diseases, Conditions, Syndromes

How to use statistics to prepare for the next pandemic

Publicly available statistics about population demographics and culture can help governments prepare for the next pandemic. We have found that by using existing socio-demographic data from early COVID-19 hot spots, where ...

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The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ (the Greek letter rho). In some cases (for instance, in the United States oil and gas industry), density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight. Different materials usually have different densities, so density is an important concept regarding buoyancy, purity and packaging. Osmium and iridium are the densest known metal elements at standard conditions for temperature and pressure but not the densest materials.

Less dense fluids float on more dense fluids if they do not mix. This concept can be extended, with some care, to less dense solids floating on more dense fluids. If the average density (including any air below the waterline) of an object is less than water (1000 kg/m3) it will float in water and if it is more than water's it will sink in water.

In some cases density is expressed as the dimensionless quantities specific gravity (SG) or relative density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas. (For example, a specific gravity less than one means that the substance floats in water.)

The mass density of a material varies with temperature and pressure. (The variance is typically small for solids and liquids and much greater for gasses.) Increasing the pressure on an object decreases the volume of the object and therefore increase its density. Increasing the temperature of a substance (with some exceptions) decreases its density by increasing the volume of that substance. In most materials, heating the bottom of a fluid results in convection of the heat from bottom to top of the fluid due to the decrease of the density of the heated fluid. This causes it to rise relative to more dense unheated material.

The reciprocal of the density of a substance is called its specific volume, a representation commonly used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.

This text uses material from Wikipedia, licensed under CC BY-SA