The information presented in this section supports the following AP® learning objectives and science practices:
5.B.10.2 The student is able to use Bernoulli's equation and/or the relationship between force and pressure to make calculations related to a moving fluid.
(S.P. 2.2)
5.B.10.3 The student is able to use Bernoulli's equation and the continuity equation to make calculations related to a moving fluid.
(S.P. 2.2)
Torricelli's theorem
[link] shows water gushing from a large tube through a dam. What is its speed as it emerges? Interestingly, if resistance is negligible, the speed is just what it would be if the water fell a distance
from the surface of the reservoir; the water's speed is independent of the size of the opening. Let us check this out. Bernoulli's equation must be used since the depth is not constant. We consider water flowing from the surface (point 1) to the tube's outlet (point 2). Bernoulli's equation as stated in previously is
Both
and
equal atmospheric pressure
(
is atmospheric pressure because it is the pressure at the top of the reservoir.
must be atmospheric pressure, since the emerging water is surrounded by the atmosphere and cannot have a pressure different from atmospheric pressure.) and subtract out of the equation, leaving
Solving this equation for
, noting that the density
cancels (because the fluid is incompressible), yields
We let
; the equation then becomes
where
is the height dropped by the water. This is simply a kinematic equation for any object falling a distance
with negligible resistance. In fluids, this last equation is called
Torricelli's theorem . Note that the result is independent of the velocity's direction, just as we found when applying conservation of energy to falling objects.
All preceding applications of Bernoulli's equation involved simplifying conditions, such as constant height or constant pressure. The next example is a more general application of Bernoulli's equation in which pressure, velocity, and height all change. (See
[link] .)
Calculating pressure: a fire hose nozzle
Fire hoses used in major structure fires have inside diameters of 6.40 cm. Suppose such a hose carries a flow of 40.0 L/s starting at a gauge pressure of
. The hose goes 10.0 m up a ladder to a nozzle having an inside diameter of 3.00 cm. Assuming negligible resistance, what is the pressure in the nozzle?
Strategy
Here we must use Bernoulli's equation to solve for the pressure, since depth is not constant.
Solution
Bernoulli's equation states
where the subscripts 1 and 2 refer to the initial conditions at ground level and the final conditions inside the nozzle, respectively. We must first find the speeds
and
. Since
, we get
Similarly, we find
(This rather large speed is helpful in reaching the fire.) Now, taking
to be zero, we solve Bernoulli's equation for
:
Substituting known values yields
Discussion
This value is a gauge pressure, since the initial pressure was given as a gauge pressure. Thus the nozzle pressure equals atmospheric pressure, as it must because the water exits into the atmosphere without changes in its conditions.
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miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
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Samuel
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Jharna
continue..
sometimes due to these physical problems..the diagnosis may be misdiagnosed.
treatment for autism.
well it depends on the severity.
since autistic kids have problems in communicating and adopting to the environment.. it's best to expose the child in situations where the child
Jharna
child interact with other kids under doc supervision.
play therapy.
speech therapy.
Engaging in different activities that activate most parts of the brain.. like drawing..painting. matching color board game.
string and beads game.
the more you interact with the child the more effective
Jharna
results you'll get..
please consult a therapist to know what suits best on your child.
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Jharna
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