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GOOD TO KNOW
Pressure in currents
Because the speed of the water increases in the narrow part of a tube,
the pressure also increases in the direction of flow. But an increase in
pressure also means an increase in force per unit of area and, thus, an
increase in the distance the narrower stream of water can shoot.
The pressure in the direction of
flow is also called dynamic
pressure, because it arises with
dynamics, or the force of
movement. In tubes, there is
always also something called
static (resting) pressure, which is
a product of the difference in
pressure between the entrance to
and exit from the tube.
Dynamic pressure is measured
against the stream, static
pressure in the stream. When the
liquid is resting, there is only
static pressure, and the dynamic
pressure is equal to zero. When
movement starts, dynamic
pressure rises and static pressure
simultaneously drops.
That also applies in reverse. In a
uniform current, in any case, the
sum of the two pressures is
always the same.
Air and Water in the Flow
THE FLOW EQUATION
If you multiply the large cross-
sectional area (A 1 ) by the
corresponding velocity (v 1 ), the
product is the same as when you
multiply the small cross-sectional
area (A 2 ) by the velocity there (v 2 ).
This equation is called the flow rate
equation or continuity equation:
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