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PHYSICS
Venturi’s principle
In everyday language, the word “
phenomenon
” is used to describe an extraordinary fact, in Physics, the term
phenomenon is used as a
description of every variation of position and state of a body
.
If a thin disc of section
S
is suspended between the fingers and moved through the air at a constant speed in a
directionperpendicular to the surfaceof thedisc: themovement causesaperceivable reaction, due to the resistance
from the air; this reaction has a constant value presuming the speed of the disc does not vary, and continues as
long as themovement lasts. Repeat the test with another disk, the surface of which is smaller than the previous
disc, for example
S/2
: maintaining approximately the same speed of movement, we note a lower air resistance.
Figure 21
Pos. 1
: we illustrate the previous experiment showing an image of the flow of air demonstrating that with equal
atmospheric pressure the resistance of the air is in proportion to the section of the body inmotion.
Pos. 2
: in this case the pressured air flows inside a body, a pipewith an internal section, i.e. the opposite situation
of Pos. 1.We denote the two sections
AA
and
BB
.
Air resistance
Movement direction
S
S/2
1
2
A
A
B
B
Fig. 21
Figure 22
Pos. 3
and
4
: at constant pressure the volume of air molecules in transit in sections
AA
and
BB
is equal and
constant regardless of the distance between the two sections: the fluid flows at a uniform speed as there are no
obstacles that oppose itsmovement.
3
AA
BB
4
Fig. 22
Figure 23
Pos. 5
and
6
: Consider a tube with a smaller central section and joined to the funnel, the incoming air is at the
same pressure as in the previous example, however corresponding to the reduced section
DD
, the air encounters
resistance to its passage. Being of constant input pressure, the air will be forced to increase speed.
5
C
C
D
D
CC
DD
6
Fig. 23
1
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