A-----------------------------B

 

If static pressure in A is higher how does it create a flow from point A to B.

If static pressure is acting perpendicular to the dotted line how can it push molecules in the horizontal direction, which is the direction of flow?

Why do you need a pressure difference to drive a flow. Can't supplying liquid with a high pressure pump to a pipe cause flow?

Edited January 7, 201015 yr by scilearner

If static pressure is acting perpendicular to the dotted line how can it push molecules in the horizontal direction, which is the direction of flow?

 

Why would this be so?

Pressure is a force per unit area, but the important point is that it is a force. In a fluid, when two pressures are unequal, that means that the two forces are unequal. And, unless there is some other force like gravity to balance it all out, an unequal force would mean that movement occurs.

 

You don't "have" to have a pressure difference to cause flow. However, because it is a fluid and rapidly deformable, any time there is a force imbalance, the pressure will adjust itself much as possible in an attempt to return to equilibrium.

 

An example of a flow without a pressure difference would be flow between two infinite parallel plates and the top plate is moving. There will be a flow because of the moving plate, but there won't be any pressure drop.

Pressure is a force per unit area, but the important point is that it is a force. In a fluid, when two pressures are unequal, that means that the two forces are unequal. And, unless there is some other force like gravity to balance it all out, an unequal force would mean that movement occurs.

 

You don't "have" to have a pressure difference to cause flow. However, because it is a fluid and rapidly deformable, any time there is a force imbalance, the pressure will adjust itself much as possible in an attempt to return to equilibrium.

 

An example of a flow without a pressure difference would be flow between two infinite parallel plates and the top plate is moving. There will be a flow because of the moving plate, but there won't be any pressure drop.

 

Hey thanks but that got me into another question?

 

---------------------------<

A(If pressure at point A is 100 mg Hg)

 

There is no fluid yet in the < region(which is a dilated part). When the tube tries to reach equilibrium 100 mg/Hg everywhere, why does the according to Bernoulli the pressure inside the dilated tube is higher? Shouldn't it be 100 mg/Hg. Also before fluid flows to < region, why isn't <region compressed due to to higher pressure outside?