Pediatrics

Play equipment that gets kids moving

Parents will be pleased to know that more is not always better when it comes to play equipment for their children.

Health

Vitamin D: How much is too much of a good thing?

When bare skin is exposed to sunlight, it makes Vitamin D, which is needed by our bodies to absorb calcium and ensure strong, healthy bones. With bathing suit skin exposure, it only takes about 10-15 minutes of sun exposure ...

Cardiology

It is never too late to start statins for clogged leg arteries

Statins are linked with reduced mortality in patients with peripheral arterial disease, even when started late after diagnosis, reports a study presented today at ESC Congress 2019 together with the World Congress of Cardiology. ...

Cardiology

It takes a community to lower cardiovascular risk

Concerted effort by friends, family and non-physician health workers can make a dramatic difference in reducing the risk factors for heart problems in patients with hypertension, an international study by Hamilton researchers ...

Diabetes

Motivational text messages help patients with diabetes

A low-cost text-messaging programme improves blood sugar control in patients with diabetes and coronary heart disease. That's the finding of the CHAT-DM randomised trial reported today at ESC Congress 2019 together with the ...

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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