Hi Tech & Innovation

New 'hyper glue' formula developed

With many of the products we use every day held together by adhesives, researchers from UBC's Okanagan campus and the University of Victoria hope to make everything from protective clothing to medical implants and residential ...

Engineering

Li-ion battery components to be printed on an inkjet printer

Scientists from Peter the Great St.Petersburg Polytechnic University (SPbPU) are developing a technology for printing the electrodes for miniature li-ion batteries using an inkjet printer. The ongoing research may help to ...

Energy & Green Tech

Wireless charging—More power, smaller package

Oak Ridge National Laboratory researchers created and tested new wireless charging designs that may double the power density, resulting in a lighter weight system compared with existing technologies, while maintaining safety.

Energy & Green Tech

Calcium batteries: New electrolytes, enhanced properties

Calcium-based batteries promise to reach a high energy density at low manufacturing costs. This lab-scale technology has the potential for replacing lithium-ion technology in future energy storage systems. Using the electrolytes ...

Energy & Green Tech

Scientists develop novel biophotovoltaics system

Researchers from the Institute of Microbiology of the Chinese Academy of Sciences have reported a novel biophotovoltaics (BPV) system based on a synthetic microbial consortium with constrained electron flow. This BPV system ...

Consumer & Gadgets

Mojo Vision shows off display technology for augmented reality

What meets the eye is important—but in the case of entering the realm of augmented reality, how it meets the eye is an issue. A California company is on that case. They have technology to let AR users keep in the flow eyes-up. ...

Machine learning & AI

One step ahead of the burglars

A new machine-learning method developed by ETH scientists makes it possible to predict burglaries even in sparsely populated areas.

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Density

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