Page 215 - WCS - Electrical

Weight m m.g vγ = Weight = m = m.g = p.g
vγ = = = = p.g Volume v m m.g
v
Weight
Volume v v vγ = = = = p.g
v
v
Volume
WORKSHOP CALCULATION & SCIENCE - CITS Mass m

m.g
Weight
m
=
=

Volume v vγ = Volume Volume = v v = p.g P = Mass = m P = Volume = v m
v
Mass
v =
v = Weight m m m.g Volume m v Volume v P = =
=
Weight
m.g
Weight
m
vγ vγ
Weight = =
= =
= =
p.g
Application of Pascal’s law = = v = p.g = Weight m m.g Volume v
Volume
Volume v v v v Weight vγ = m = = = p.g Mass m

P =
Volume
v
v
Volume
v
1 Hydraulic jacks are used to lift heavy load of vehicle when tyre of vehicle has to be changed. = v
v =
=
Volume

Volume m
v
Weight
Mass
2 Hydraulic brakes are used in cars and motorcycles. Mass = = m m Mass m
Weight
v m
Volume
m.g
v
=
=
P = P =
v vγ =
Volume p.g==
=
v v
= Volume
=

Volume
m v
Mass
2

Mass v = v =
= =
v
m v
Volume
Volume
Volume
v
=
=
2
3 Hydraulic pumps are used to raise cars in a motor workshop. v Volume v v P = Volume = v
m m
Weight
=
v =
Weight
m
Mass
2
m

Weight
Volume
v
4 Hydraulic presses are commonly used for forging, punching and metal forming operation.

v
Mass
=
=
m
m
Volume
2
Mass
of
Density v = any substance v Density of any substance P = Volume = v
Newton’s law of viscosity
=

Volume
v v
substance
m
Weight
v v
4 =
Density of water = at Volume = = m m D Density oensity of any f water v at = 4 c ° Volume = v
c °
Newton’s law of viscosity states that the shear stress is directly proportional to the the rate of shear strain or
Mass
2 2

of
at
Density
water
velocity gradient Mass Density of any substance 4 c ° Mass m
2

du
Volume v Density of water at 4 c °
du
τα
v τα Density ofDensity == of any substanceany substance dy
du
2 dy Mass m τα Density of any substance
4 4 t
at a r
Where μ= Coefficient of dynamic viscosity dy Density of water at 4 c °
c ° c°
of wateof
Density

Density
water

du τα du du
= Velocity gradient or rate of shear strain
Density dy any substance dy du
of
dy
Density of wate du du c ° dy du
τα τα 4 at r
dy dy
Coefficient of Viscosity du τ τα

τ
μ
=
μ = dy  du τ  dy
 du  μ =  
  dy   du du du    du   
dy
 τα

dy dy dy μ = τ    dy    du
 du   dy


τ τ


dy
2
Thus viscosity is also defined, as the shear stress is required to produce unit rate of shear strain.


μ μ
du
= =

2

stress
Shear

N/m
Newton

sec
τ
N/m

μ
 
=
dy
μ = Shear stress  du du μ = Newton sec Velocity  = =  du 2 = Newton sec
= 
S.I. unit of viscosity  

N/m
ofstress r


m/s 

Shea
Change
2
 
 
m/s
 Change of Velocity  dy  μ =  2  =   = m
dy
       Change of of Velocity     2 dy  2
m 

m
Change
m/s
distance 


τ

 Change of μ = distance  μ = m  Shear  Change of distance =  N/m m = Newton m sec
stress



Velocity 
 du      Change of 2   m/s m 2


2

dy
Dyne.sec  sec Newton sec Newton
N/m
N/m
Shear
m
Dyne.sec
= =
μ = μ =  Shea  stress r stress   Change of distance  Shear stress N/m 2 Newton sec
= =
2
of Velocityof
 Change Velocity   m/s m/s μ = cm.sec of Velocity  = m/s = 2

Dyne
Change
2 2

2
cm
 
 
 m m
Change
 
distance f
Change
of o
Change


Unit of viscosity in CGS   m m cm 2 of distance    m m
 
distance 

 2
Dyne.sec Change

Newton

sec
Newton
μ = Shear stress = N/m = Newton sec sec
2
cm
The unit of viscosity in CGS is called as poise, which is equal to
 Change of Velocity  m/s New m sec ton
2
2

  m 2 Dyne.sec m
Dyne.sec

 Change of distance  2 2 m 1 m 2 Dyne.sec
1 cm cm Newton sec 2
100 m 2 100 1 cm
Dyne.s ec sec 100
Newton sec Newton
10 poise = 1 Newton sec
2 2
Force
Force cm 2 m m 100 m 2
Area
1 1
Area
1 centi poise = poise Force 1
sec

Newton
Area
100
m 2 100 Force 100
Area
The viscosity of water at 20°C is 0.01 poise or 1 centipoise
1
Force
Force
100
Pressure or Intensity of Pressure Force
Area
Area
Area
It is defined as the normal surface force acting per unit area. It is denoted by ‘p’ S.I. unit N/m² i.e. Pascal
Force
P= Area
When a fluid is contained in a vessel, it exerts force at all points on the sides and bottom of the container. The
force per unit area is called as pressure
The pressure of a fluid on a surface will always act normal to the surface.
202
CITS : WCS - Electrical - Exercise 19