News tagged with density

Stem cell type resists chemotherapy drug

A new study shows that adipose-derived human stem cells, which can become vital tissues such as bone, may be highly resistant to the common chemotherapy drug methotrexate (MTX). The preliminary finding from ...

Jul 02, 2014
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Growth hormone related with signs of aging

The decreased production of growth hormone is caused by a physiological process known as somatopause, which practically affects the entire body, since it's involved in body composition, metabolism, bone mineral ...

Jun 16, 2014
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Study identifies 41 powerhouse fruits and vegetables

(HealthDay)—Forty-one powerhouse fruits and vegetables (PFV) have been classified and validated, according to a study published online June 5 in the U.S. Centers for Disease Control and Prevention's Preventing Ch ...

Jun 10, 2014
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Melatonin makes old bones stronger

Faleh Tamimi, a professor in McGill's School of Dentistry, is the leader of a research team that has just discovered that melatonin supplements make bones stronger in elderly rats and therefore, potentially, in elderly humans ...

May 27, 2014
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New software aids breast cancer risk assessment

Researchers of the Universitat Politècnica de València, in collaboration with the Instituto de Salud Carlos III and the Foundation for the Health and Biomedical Research of the Comunitat Valenciana, have ...

May 09, 2014
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Team identifies genes influencing bone density

(Medical Xpress)—Geneticists have taken a major step forward in the battle against osteoporosis by identifying two genes that play critical roles in regulating bone mineral density. By targeting those genes ...

May 06, 2014
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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