Inside a pipe or tube a very thin layer of fluid right near the walls of the tube are motionless because they get caught up in the microscopic ridges of the tube. Layers closer to the centre move faster and the fluid sheers. The middle layer moves the fastest.

Lets take a example of pipe

 Inside a pipe or tube a very thin layer of fluid right near the walls of the tube are motionless because they get caught up in the microscopic ridges of the tube. Layers closer to the centre move faster and the fluid sheers. The middle layer moves the fastest.

Specific mass or density (𝞺)

 The “mass per unit volume” is mass density. Hence it has units of kilograms per cubic meter (kg/m3).

Specific mass or density (𝞺) = 𝑀𝑎𝑠𝑠/𝑉𝑜𝑙𝑢𝑚𝑒{𝑘𝑔/𝑚3}

 The mass density of water at 4o C is 1000 kg/m3 while it is 1.20 kg/m3 for air at 20oC at standard pressure.

Specific weight or weight density (𝟂 or 𝞬)

 It is the ratio between the weight of a fluid to its volume. It is also termed as weight per unit volume of a fluid. Its unit is N/m3.

Specific Weight (𝟂) = 𝑊𝑒𝑖𝑔ℎ𝑡/𝑉𝑜𝑙𝑢𝑚𝑒 = 𝑚𝑎𝑠𝑠 ×𝑔𝑟𝑎𝑣𝑖𝑡𝑦 / 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝞺𝒈{𝑁/𝑚3}

Problem:

1. What is the specific weight for water at 4oC is ……..

2. What is the specific weight for air ……….