Know your numbers: What is your heart rate?

Your heart rate, or pulse, is the number of times your heart beats per minute. Your resting heart rate is when the heart is pumping the lowest amount of blood you need because you're not exercising.


Expert advice for women with thinning hair

Thinning hair is common as we age. And while the signs might not be as obvious as in men, about 55% of women experience some hair loss by the time they're 70. Treatments to prevent or stop it can help many women who are losing ...


Lipoprotein(a): What to know about elevated levels

If you've listened to the radio or opened a webpage in the past year, you may have seen or heard ads promoting lipoprotein(a), or Lp(a), testing to help people identify risks for heart disease.

Gerontology & Geriatrics

Impacts during everyday physical activity can slow bone loss

A study conducted at the University of Jyväskylä, Finland, found that the bone mineral density at the femoral neck decreased, but the structural properties were maintained or even slightly improved during a year-long multicomponent ...

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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