- #71
klimatos
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rcgldr said:1) This would violate Newton's third law. The downwards force of gravity on the water is equal and opposite of the upwards force of the river bed. The pressure at the river bed corresponds to the force per unit area at the river bed, and that force corresponds to the weight of the water, regardless of the speed of the water. Unless there is a vertical component of acceleration of the water, the force on the river bed corresponds to the weight of the water in the river, and so does the pressure.
2) The Bernoulli relationship between speed and pressure only applies when acceleration of a gas or fluid is due to a pressure gradient within that gas or fluid.
3) Getting back on topic, water vapor, temperature, and vertical accelerations of the atmosphere can affect the pressure. Wiki articles:
http://en.wikipedia.org/wiki/Low-pressure_area
http://en.wikipedia.org/wiki/High-pressure_area
4) In the case of a closed container experiencing the force of gravity (acceleration at 1 g would cause the same effect), there will be a pressure differential within the container, such that the net downwards force on the container by the gas inside the container will exactly equal the weight of the gas inside the container (if there is no vertical component of acceleration of the gas within the container).
1) Simply not true. Check any textbook on hydraulics. I seem to remember from a book on hydraulic geomorphology that even moderately moving rivers can use the pressure differential to lift boulders weighing many tons from river beds. I believe the lifting power was proportional to the fourth power of the velocity.
2) Not true, It applies whenever and wherever there is fluid motion. Again, check a hydraulics textbook.
3) Gee. Haven't I been saying all along that net atmospheric motions (winds) affect surface pressures?
4) I have no interest in closed containers. The atmosphere is not a closed system.