Glossary of elastomer processing
Specific weight
Specific weight is a physical quantity that describes the ratio of the weight force of a material to its volume. It is usually stated in newtons per cubic metre (N/m³) and is used to evaluate the density of a material in relation to gravity. In practice it is often equated with density (mass per volume), but it differs in that it takes weight force rather than mass into account.
The specific weight of a material is calculated using the following formula:
γ = ρ × g
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γ: specific weight (N/m³)
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ρ: density of the material (kg/m³)
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g: acceleration due to gravity (≈ 9.81 m/s²)
An example: for a material with a density of 1,000 kg/m³ (e.g. water), the specific weight is:
γ = 1,000 kg/m³ × 9.81 m/s² = 9,810 N/m³
Specific weight is a decisive factor in evaluating the mechanical properties and behaviour of a material under load:
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Material comparison: allows materials to be distinguished in terms of their weight and density.
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Stability analysis: important in structural analysis and design engineering for calculating loads.
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Transport and handling: affects the logistics and processing of materials.
| Material | Density (kg/m³) | Specific weight (N/m³) |
|---|---|---|
| Water | 1,000 | 9,810 |
| Concrete | 2,400 | 23,544 |
| Steel | 7,850 | 76,923 |
| Rubber (elastomer) | 1,100 to 1,500 | 10,791 to 14,715 |
| Polyethylene (PE) | 950 | 9,320 |
Specific weight is important in numerous industries:
Rubber and plastics industry
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Materials testing: analysing the density of elastomers and plastics for quality control.
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Product development: optimising the material composition for lightweight construction or specific requirements.
Hydraulics and fluid technology
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Calculating buoyancy: determining the forces in the interaction between liquids and solids.
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Choice of material: using specific weights to select seals or coatings.
Accurate determination of specific weight can be affected by the following factors:
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Temperature: changes in temperature affect density and therefore specific weight.
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Moisture: hygroscopic materials can absorb moisture and change their mass.
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Material homogeneity: inhomogeneous materials can give inaccurate results.
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How does specific weight differ from density? Density is mass per volume (kg/m³), while specific weight describes weight force per volume (N/m³).
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Why is specific weight important? It allows precise calculations in structural analysis, materials testing and product development.
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Can the specific weight of a material be changed? Yes, through changes in the material composition or external influences such as temperature.
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How is specific weight measured? It is measured indirectly via the density of the material, which is then multiplied by the acceleration due to gravity.
Specific weight is an essential parameter for evaluating materials in terms of their density and weight force. It is widely used in the elastomer and plastics industry, in materials testing and in planning and calculation, where precise weight assessments and load analyses are of great importance. Thanks to its versatile uses, specific weight remains an indispensable tool in materials science.
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