Difference Between Specific Gravity and Specific Weight

Specific Gravity vs Specific Weight

Specific gravity and specific weight are two quantities widely used. These two concepts are widely used in fields such as mechanics, thermodynamics, fluid mechanics, aerodynamics and various other fields. It is vital to have a proper understanding in these concepts in order to excel in fields which have usages of these concepts. In this article, we are going to discuss what specific gravity and specific weight are, their similarities, the definitions of specific gravity and specific weight, the applications of these two and finally the difference between specific gravity and specific weight.

Specific Gravity

Specific gravity is defined as the mass of a unit volume of the given material divided by the mass of the unit volume of the reference material. The density of a material tells you how close the molecules are packed and how heavy the molecules are. The density is defined as the mass of a substance per unit volume. This is mathematically written as density = mass / volume. The reference material is air for gases and water for liquids most of the times. Specific gravity is also pressure and temperature dependent. Specific gravity is used in simple industries such as milk and rubber, to determine the quality of the raw materials. Pycnometer is one of the many different instruments used to determine the specific gravity. It is also known as a specific gravity bottle. Specific gravity is a dimensionless quantity, which varies between zero and infinity. But it cannot have the value zero itself. Specific gravity also has a form called the apparent specific gravity. Specific gravity is also known as relative density, which is defined as density of the given material / density of the reference material.

Specific Weight

Specific weight is a similar sounding word of specific gravity but these are two very different quantities. Weight is defined as the force on a mass due to the gravitational field of another object. Since weight is a force, it’s measured in newton. Specific weight is defined as the weight of a unit volume of the material. The Greek letter gamma (γ) is used to denote the specific weight. The units of specific weight are Newton per square meter. The dimensions of specific weight are [mass] [length]^-2[time]^-2. The specific weight is also equal to the density of the material multiplied by the gravitational field intensity acting on the object. The specific gravity is dependent on the gravitational field.

What is the difference between Specific Gravity and Specific Weight? • Specific gravity is a dimensionless quantity whereas specific weight has dimensions. • The specific gravity of a material is independent of the gravitational field, but the specific weight of a material is dependent on the gravitational field. • The specific gravity is a comparison between two materials but the specific weight is not. In other words, specific gravity is a relative quantity whereas specific weight is an absolute quantity.