We explain what specific weight is and what the formulas are to calculate it. Also, some examples and their relationship with density.
What is specific weight?
The specific weight is the existing relationship between the weight and the volume that occupies a substance in space. It is the weight of a certain amount of substance divided by the volume it occupies. In the International System it is expressed in units of Newtons about cubic meter (N/m3).
The calculation of specific gravity requires other properties of the substance, such as density and mass. Mathematically, the specific gravity It 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 = mg/V, where m is the mass of the substance and g is the acceleration of gravity (commonly considered as 9.8m/s2). As the density (ρ) of a substance is defined as m/Vthe specific weight can be written as γ=ρ.g.
Examples of specific weight
Some examples of specific weight 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
- Iron casting: 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 the specific weight (mg/V) and the density (m/V) is analogous to that which exists between the weight (mg) 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 is, the more mass that enters a certain volume, the greater its specific weight will be, since the greater “mass due to gravity” will enter that volume.
