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7.What's phenomenon internal friction or viscosity ?
8. What does the Newton's law of viscosity state ?
9.What's unit of viscosity?
10. What does Poiseuille's law state ?

11 What does Stoke′s law state?
12 What's Reynolds number?

7.10 Problems

Air blows out through the horizontal tube AB as shown in

fig.7.12 .The volume rateQ of air is equal to 1 liter per minute .There
2 2
are two cross section in tube :S  2sm ,S  5 , 0 sm . Calculate the
1
2
difference of water levels in a tube
which connects two parts of tube AB.
kg
Air density  a  , 1 32 3 , water
m

kg
density  w  1000 3 .
m
Solution
According to Bernoulli's equation

for the horizontally located tube of
Figure7.12
flow of ideal liquid or gas:

2 2
 a v  1  a v  2
p   p 
1 2
2 2
we will get

 2 2
 p  p  p  (v  v 1 ).
2
2
1
2
Taking into account that

Q Q
Q  S  v  S v   v  and v 
1 1 2 2 1 2
S S
1 2
therefore
2 2 2
 Q  S 1  S 2 
p    .
2  S 1 2  S 2 2 


Substitute all values and obtain p  750 Pa

98