IEMDaily - Video Lecture Notes

Formula

Units of Pressure

In SI system the unit of pressure is pascal (Pa). It is defined as force of one Newton per square meter.

1 P a = 1 N / m^{2} = 1 k g / m s^{2}

In CGS system the unit of pressure is

1 d y n e / c m^{2}

The standard atmosphere (atm) is an established constant. It is approximately equal to typical air pressure at earth (sea level) and is defined as

101325 P a

Pressures are also commonly expressed as depth of a particular fluid. (eg. as centimeters of water or millimeters of mercury)
The following are some conversions of units of pressure,

1 b a r = 10^{5} P a

1.01325 \times 10^{5} P a = 1 a t m

1 T o r r = 1 m m o f H g

and

760 m m o f H g = 1 a t m

Definition

Thrust

It is a kind of force exerted by an object perpendicular to the surfaces.

Result

Relationship between thrust and pressure

Thrust is the total force acting perpendicular to the surface of body while pressure is the thrust per unit area. Unit of thrust is

N

while unit of pressure is

N / m^{2}

Pressure = \frac{Thrust}{Area}

Definition

Differences Between Solids and Liquids

1.A solid is a state of matter that has a definite shape and volume while a liquid is a state of matter that has volume but no definite shape.
2.A liquid takes the shape of the container that holds it while a solid has a shape of its own.
3.The atoms in a solid are bound tightly together causing it to become compressed, and it can only vibrate while the atoms in a liquid, although bound together, are temporary which allows them to flow.
4.Solids are strong, tough, elastic, ductile, and flexible while liquids are not.
5.Examples of solids are wood, stones, trees, and soil while examples of liquids are water, oil, mercury, and ethanol.

Definition

Properties of fluids

Properties of determine how fluids can be used. They also determine the behaviour of fluids in fluid mechanics. The following are some of the important basic properties of fluids:
     1.Density: Density is the mass per unit volume of a fluid. In other words, it is   the ratio between mass (m) and volume (V) of a fluid.
   2.Viscosity: Viscosity is the fluid property that determines the amount of   resistance of the fluid to shear stress. It is the property of the fluid due to which the fluid offers resistance to flow of one layer of the fluid over another adjacent layer.

   3.Temperature: It is the property that determines the degree of hotness or coldness or the level of heat intensity of a fluid. Temperature is measured by using temperature scales.

   4.Pressure: Pressure of a fluid is the force per unit area of the fluid. In other words, it is the ratio of force on a fluid to the area of the fluid held perpendicular to the direction of the force.

5.Specific Volume:

Specific volume is the volume of a fluid (V) occupied per unit mass (m). It is the reciprocal of density.

6.Specific Weight:

Specific weight is the weight possessed by unit volume of a fluid. It is denoted by

w

. Its unit is

N / m^{3} .

7.Specific Gravity:

Specific gravity is the ratio of specific weight of the given fluid to the specific weight of standard fluid. It is denoted by the letter

S

. It has no unit.

Result

Characteristics of liquid pressure

Following are the characteristics of liquid pressure
1) liquid exerts pressure on the wall of container.
2) pressure force increases as the depth of liquid increases.
3) pressure force will be same at all points inside the liquid at equal depth.

Definition

Pressure of liquid depends on gravitational force

The pressure of a liquid can be calculated by using a formula:

p = h d g

p =

pressure of a liquid

h =

height of the liquid column

d =

density of the liquid

g =

acceleration due to gravity

Example

Pressure of liquid on walls of container

When water is filled in a bucket, the water exerts a force on the walls of the bucket from inside. If the strength of the bucket is low, the pressure may cause the bucket to burst.

Example

Pressure on the walls of container

A gas volume consists of molecules and every molecule has some kinetic energy. These molecules when collide with the walls of a container apply pressure on it. This can be demonstrated by the tin can experiment. Fill the can with water and boil it. After that seal the can with a stopper so that can contains steam at low pressure. Now pour cold water on the can from outside. It is observed that the can collapses inwards. This happens because when cold water is poured, steam inside condenses and air pressure inside reduces. The difference in pressure inside and outside causes a force applied on the outer walls of the container. This force causes the tin can to crush inwards. Hence, it demonstrates that pressure is applied by air molecules on the container.
Note:
The tin can retains its shape usually because the force applied by the gas molecules on the outside of the container is balanced by the force inside the container.

Definition

Properties of liquid pressure

Liquid pressure at same horizontal level of liquid is same.
Though pressure opposite to the surface, it is a scalar quantity.
Pressure at a point in a liquid is same in all directions.

Result

Factors affecting a pressure in a liquid

Following are the factors which affect the pressure at a point in liquid
1) Density of liquid (

ρ

)
2) Depth of liquid (

h

)
3) Acceleration due to gravity (

g

)
Pressure in a liquid at a depth is given by

P = h ρ g

Example

Characteristics of liquid pressure

These are the following characteristics of liquid pressure: -
1. Increase with depth.
2. Acts in all directions.
3. Does not depend on the area of its surface.
4. Does not depend on the shape or size of the container.
5. The pressure at the two point at the same level in the same liquid is same.