News tagged with density

Less body fat for toddlers taking vitamin D

A healthy intake of vitamin D in the first year of life appears to set children up to have more muscle mass and less body fat as toddlers, according to a new study published in the journal Pediatric Obesity.

23 hours ago
popularity3 comments 0

Review compares metformin, OCP for teens with PCOS

(HealthDay)—For adolescents with polycystic ovarian syndrome (PCOS), treatment with metformin and oral contraceptive pills can be beneficial, although evidence is limited, according to a review published online April 28 ...

Apr 28, 2016
popularity9 comments 0

The more you run, the denser your bones will be

Spanish researchers have analysed the effect of endurance running training on the stiffness index, a variable that is directly related to bone quality. The results confirm that the greater the race distance that is trained, ...

Apr 19, 2016
popularity40 comments 0

Genetic vitamin K1 levels linked to heart disease

(HealthDay)—Genetically determined vitamin K1 is associated with coronary artery disease (CAD) and myocardial infarction (MI), according to a study published online April 8 in the Journal of Thrombosis and Haemostasis.

Apr 18, 2016
popularity5 comments 0

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

Subscribe to rss feed