### Common Fluid Properties

• Define the terms in relation to fluid mechanics such as density, specific gravity, viscosity and vapor pressure.

### Solved Example:

#### 60-1-01

Fluid is a substance that: (TANGEDCO AE EC 2018)

Solution:
Fluids include liquids and gases. While gases always expand till they fill any container, liquids do not.
One of the defining characteristics of fluids is they cannot resist shear stresses (like what solids can), and on application of shear stresses, they start deforming or flowing.

### Solved Example:

#### 60-1-02

Practical fluids:

Solution:
Practically, fluids have properties such as viscosity, compressibility as well as surface tension.

### Solved Example:

#### 60-1-03

Density of water is maximum at:

Solution:

Water exists in liquid format between 0-100 C. Generally density of liquid increases as temperature is reduced. However, water has a small exception. Water displays abnormal behavior between 0-4 Degree Celsius when the density actually decreases as the temperate decreases.

### Solved Example:

#### 60-1-04

Poise is the unit of: (SSC JE ME Paper 4- Jan 2018 Morning)

### Solved Example:

#### 60-1-05

Choose the correct relationship:

Solution:
$\mathrm{Kinematic\ viscosity} = \dfrac{\mathrm{Dynamic\ Viscosity}}{\mathrm{density}}$ $\mathrm{Dynamic\ viscosity} = \mathrm{Kinematic\ Viscosity} \times \mathrm{density}$

### Solved Example:

#### 60-1-06

Choose the wrong statement:

### Solved Example:

#### 60-1-07

Kinematic viscosity is equal to: (UPSSSC JE Mech 2015- Paper 2)

### Solved Example:

#### 60-1-08

Viscosity of water in comparison to mercury is: (ISRO Scientist Mechanical 2013)

Solution:

Dynamic viscosity of water at 27$^\circ C$ = 0.89 centipoise whereas that of mercury at same temperature = 1.53 centipoise, so dynamic viscosity of mercury is higher than water.

However, kinematic viscosity is ratio of dynamic viscosity to density and mercury is 13.6 denser than water.

Once you divide by higher density of mercury, the kinematic viscosity of mercury is much lesser than water. (water = $1 \times 10^{-6} m^2/s$ compared to mercury = $0.115 \times 10^{-6} m^2/s$)

### Solved Example:

#### 60-1-09

Surface tension has the units of: (MPSC AMVI Official Paper 1: Set A/2017)

Solution:

Surface tension is force per unit length, hence its units will be N/m.

### Solved Example:

#### 60-1-10

Property of a fluid by which molecules of different kinds of fluids are attracted to each other is called:

Solution:

Adhesion is attraction between unlike molecules whereas cohesion is attraction between like molecules.

### Solved Example:

#### 60-1-11

Specific weight of water in S.I. units is equal to:

### Solved Example:

#### 60-1-12

Which of the following is dimensionless? (NPCIL SA/ST ME GJ Nov 2019- Shift I)

### Solved Example:

#### 60-1-13

The tendency of a liquid surface to contract is due to the following property:

### Solved Example:

#### 60-1-14

A fluid in equilibrium can't sustain: (ISRO Scientist Civil 2015)

Surface tension:

### Solved Example:

#### 60-1-16

The property of fluid by virtue of which it offers resistance to shear is called: (ISRO VSSC Technical Asst. Mechanical April 2012)

### Solved Example:

#### 60-1-17

Kinematic viscosity is dependent upon:

### Solved Example:

#### 60-1-18

Surface energy per unit area of a surface is numerically equal to:

### Solved Example:

#### 60-1-19

Choose the wrong statement:

### Solved Example:

#### 60-1-20

Surface energy per unit area of a surface is numerically equal to:

### Solved Example:

#### 60-1-21

If 850 kg liquid occupies volume of one cubic meter, means 0.85 represents its:

### Solved Example:

#### 60-1-22

The property by virtue of which a liquid opposes relative motion between its different layers is called:

### Solved Example:

#### 60-1-23

The process of diffusion of one liquid into the other through a semi-permeable membrane is called:

### Solved Example:

#### 60-1-24

Free surface of a liquid tends to contract to the smallest possible area due to force of:

### Solved Example:

#### 60-1-25

The kinematic viscosity is the: (AFCAT EKT Mechanical Paper 4- Set 01/2014)

### Solved Example:

#### 60-1-26

A piece of metal of specific gravity 7 floats in mercury of specific gravity 13.6. What fraction of its volume is under mercury ? (SSC Jr. Engg. Mechanical 2018)

If 5.6$m^3$ of oil weighs 46800 N, What is the relative density of the oil?
$\mathrm{Mass} = \dfrac{W}{g} = \dfrac{46800}{9.8} =4770.61\ kg$ $\mathrm{Density} = \dfrac{m}{V} = \dfrac{4770.61}{5.6} =851.90\ kg/m^3$ $\mathrm{Relative\ density} = \dfrac{\rho_{\ \mathrm{fluid}}}{\rho_{\ \mathrm{water}}} = \dfrac{851.9}{1000} = 0.852$