Specific weight

The weight density, and the specific gravity of a physical body is the ratio of its weight to its volume.

The DIN since 1938 recommends to German standard work, the term " specific gravity " in favor of " Wight" give up. From 1971 to 1984, the specific gravity was avoided in DIN 1306. The unit weight is rarely used today in physics and engineering. Is preferably given the density of a body, of which the specific weight can be derived, if necessary.

Definition

The specific gravity of a material is its weight relative to its volume

Symbols of gravity is (Greek gamma )

The unit of gravity is:

Dependencies

The force acting on a body weight force is proportional to the gravitational acceleration (represents the mass ):

Therefore the value of specific gravity of a material is dependent on the strength of gravity, for example, the value of specific gravity on the moon only about 1/6 as large as on the earth surface. Even on Earth, the gravity is different depending on the location: so the acceleration due to gravity at the North Pole is due to the Schwereabplattung by half a percent higher than at the equator, it is also on a mountain less than at sea level.

In addition, the weight can be reduced by buoyancy when the sample to be measured body is surrounded by a medium. Then his weight is reduced according to the Archimedes principle the weight of the displaced fluid, which is especially noticeable when using water as medium. But the air of the atmosphere causes a measurable boost in this way is the air pressure in the value of the unit weight a.

The value of the specific gravity so that depends not only on the type of material, but also on the place and the conditions in which the weight is measured. This is in contrast to the density depends only on the mass and the volume of the body under consideration:

The temperature of a sample has an influence on the value of the unit weight, since the volume changes of the sample by thermal expansion. This is also the case with the density.

In order to obtain a unique value for the specific gravity of a material despite these dependencies, it is common to derive their value standard conditions for acceleration due to gravity, air pressure and temperature.