Specific gravity is defined as the ratio of the density of a given substance to the density of water, when both are at the same temperature, it is therefore a dimensionless quantity (see below). The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Substances with a specific gravity greater than one are denser than water, and so (ignoring surface tension effects) will sink in it, and those with a specific gravity of less than one are less dense than water, and so will float in it. For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to Specific gravity is a special case of, or in some usages synonymous with, relative density, with the latter term often preferred in modern scientific writing. Relative density, sometimes called specific density, is the Ratio of the Density of a substance to the density of a given reference material The use of specific gravity is discouraged in technical use in scientific fields requiring high precision — actual density (in dimensions of mass per unit volume) is preferred.
Specific gravity, SG, is expressed mathematically as:
where 
is the density of the substance, and 
is the density of water. (By convention ρ, the Greek letter rho, denotes density. Rho (uppercase Ρ, lowercase ρ or ϱ) is the 17th letter of the Greek alphabet. ) The density of water varies with temperature and pressure, and it is usual to refer specific gravity to the density at 4°C (39. 2°F) and a normal pressure of 1 atm. The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm In this case is equal to 1000 kg·m−3 in SI units (or 62. 43 lb·ft−3 in United States customary units). US customary units, also known in the United States as English units or Imperial units (in reference to the British Empire) (but see English
Given the specific gravity of a substance, its actual density can be calculated by inverting the above formula:
Occasionally a reference substance other than water is specified (for example, air), in which case specific gravity means density relative to that reference.
Specific gravity is by definition dimensionless and therefore not dependent on the system of units used (e. In Dimensional analysis, a dimensionless quantity (or more precisely a quantity with the dimensions of 1) is a Quantity without any Physical units g. slugs·ft−3 or kg·m−3). The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it However, the two densities must of course be converted to the same units before carrying out the numerical ratio calculation.
For information about the measurement of and uses of specific gravity, see relative density. Relative density, sometimes called specific density, is the Ratio of the Density of a substance to the density of a given reference material
Contents |
Examples
- Balsa wood has a specific gravity of 0. 2, so it is 0. 2 times as dense as water.
- Aluminium has a specific gravity of 2. WikipediaNaming 7, so it is 2. 7 times as dense as water.
- Lead has a specific gravity of 11. Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly 35, so it is 11. 35 times as dense as water.
(Samples may vary, and these figures are approximate. )
See also
- API gravity
- Buoyancy
- Density
- Fluid mechanics
- Gravity (beer)
- Hydrometer
- Pycnometer
External links
Books
- Fundamentals of Fluid Mechanics Wiley, B. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Fluid mechanics is the study of how Fluids move and the Forces on them A hydrometer is an instrument used to measure the Specific gravity (or Relative density) of Liquids that is the ratio R. Munson, D. F. Young & T. H. Okishi
- Introduction to Fluid Mechanics Fourth Edition, Wiley, SI Version, R. W. Fox & A. T. McDonald
- Thermodynamics: An Engineering Approach Second Edition, McGraw-Hill, International Edition, Y. A. Cengel & M. A. Boles
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic