Density of Water and Specific Weight of Water

Density of Water and Specific Weight of Water Points : density of water and specific weight of water Density of Water The density (or mass density) of a liquid may be defined as the mass per unit volume at a standard temperature and pressure and is usually denoted as (p). Mathematically density,

P = Mass/Volume

Note: The variation in the density of water, with the variation of pressure and temperature, is so small, that for all practical purposes it is generally neglected.

Example: If 2.5 m³ of a certain oil has a mass of 20 tones find Its mass density.

Solution
Given
Volume 2.5 m² and mass 20 tones
We know that mass density of the oil,
P= Mass/Volume = 20/2.5 =0.8 t/m3 = 800 kg / m³ Ans. Specific Weight of Water The specific weight (or weight density) of a liquid may be defined as the weight per unit volume at the standard temperature and pressure and is usually denoted as (w).

Mathematically specific weight,
W = Weight/Volume

Note: The variation in the specific weight of water, with the variation of pressure and temperature, is also so small, that for all practical purposes, it is generally neglected. It is also known as weight density.

For the purposes of all calculations, relating to hydraulic. Fluid Mechanics and Hydraulic Machines, the specific weight of water is taken as 9.81 kN/m³. However, the following table gives the values of specific weights of water at different temperatures as per manual 25 of American’s Society of Civil Engineers.