We explain what the specific weight is and what are the formulas to calculate it. Also, some examples and their relationship with density.
What is specific gravity?
Specific gravity is the relationship between theweight and thevolume that occupies asubstance at space. It is the weight of a certain amount of substance divided by the volume it occupies. At International system is expressed in units of Newtons about cubic meter (N / m3).
The calculation of the specific gravity requires other properties of the substance, such as density and the mass. Mathematically, the specific gravity is represented by the symbol gamma (γ) and is expressed as:
γ (specific weight) = w (ordinary weight) / V (volume of substance), or what is the same: γ = w / V = m.g / V, wherem is the mass of the substance andg is theacceleration of thegravity (commonly regarded as 9.8 m / s2). Like density (ρ) of a substance is defined as m / V, can be written to the specific gravity as γ = ρ.g.
Examples of specific gravity
Some examples of specific gravity of different materials are:
- Gypsum: 1250 N / m3
- Cal: 1000 N / m3
- Dry sand: 1600 N / m3
- Wet sand: 1800 N / m3
- Loose cement: 1400 N / m3
- Concrete tiles: 2200 N / m3
- Poplar wood: 500 N / m3
- Ash wood: 650 N / m3
- American pine wood: 800 N / m3
- Steel: 7850 N / m3
- Aluminum: 2700 N / m3
- Bronze: 8600 N / m3
- Lead: 11400 N / m3
- Zinc: 7200 N / m3
- Cast iron: 7250 N / m3
- Water: 1000 N / m3
- Asphalt: 1300 N / m3
- Stacked paper: 1100 N / m3
- Slate: 2800 N / m3
- Tar: 1200 N / m3
- Granite: 2800 N / m3
Specific weight and density
The relationship between specific weight (g / V) and the density (m / V) is analogous to that between the weight (m.g) and the dough (m) of a substance. It is evident that the more mass a certain amount of a substance has, the greater its weight. In the same way, the denser that amount of substance, the more mass that enters a certain volume, the greater its specific weight, since the greater "mass by gravity" will enter that volume.