Question about the difference of pressure between two point in a liquid

In summary: Wouldn't that be the total pressure?The transmitted pressure would be the total pressure, but you would also have to take into account the weight of the liquid.
  • #1
kakuta
6
0
Hi guys, sorry if the question seems too basic or simple, but i can't seem to grasp the concept about pressure here.

say, a cylinder filled with water;
------------
°A


°B

------------

at point A, the liquid pressure is lower than it is at point B ,
as there's a difference in pressure between the two region, why wouldn't the water at region B flows up to region A due to its higher pressure ?

from what I've read in my reference book,
water from a high region (reservoir ) flows down to a lower region(ground level) is able to flow back up to water tanks (above ground lvl) at our houses due to the high pressure at lower region when water flows down from reservoir at a great height,
in accordance to p=ρhg

have i got pressure and force mixed up ?

why wouldn't water at the bottom pushes upward in a cylinder/bottle due to greater pressure under it ?
at the same time, why would water flow upwards to water tanks located above the ground lvl?
is it because of the great height difference between reservoir and ground level hence the great pressure?
how does water remain still in a cylinder with all that pressure difference?

sorry again for my grammar and phrasings , and thanks in advance for all the help !
 
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  • #2
If you put a tube through the cylinder wall at B, sealed it and bent it upward to the top of the cylinder, the water would flow up the tube, to A and up to water level.

This is how your water can flow upward, because the water level (at the reservoir) is higher than your tanks.

Water is moving around in the cylinder but any water that may flow from A to B, will quickly be replaced by more water.
 
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  • #3
What about water flowing from B to A seeing how the pressure at B is greater than at A which causes a movement due to the difference in pressure? Does something like that happens in water?
Until it reaches state of equillibrium or some sort
 
  • #4
kakuta said:
What about water flowing from B to A seeing how the pressure at B is greater than at A which causes a movement due to the difference in pressure? Does something like that happens in water?
Until it reaches state of equillibrium or some sort

The pressure difference just supports the weight of the liquid between A and B. The system is in static equilibrium.
 
  • #5
Chestermiller said:
The pressure difference just supports the weight of the liquid between A and B. The system is in static equilibrium.

In other words, pressure in liquid is present to support the weight of the liquid above it hence the pressure increases when the depth increases as weight of water increase? Is it safe to say that way?
 
  • #6
There may be a pressure difference, but the liquid at B does not accelerate upwards because there is no resultant force. The force due to a pressure difference is balanced by the weight of the liquid under gravity. This is the hydrostatic equilibrium.
 
  • #7
kakuta said:
In other words, pressure in liquid is present to support the weight of the liquid above it hence the pressure increases when the depth increases as weight of water increase? Is it safe to say that way?

Yes. This is exactly what is happening. As MikeyW pointed out, this is called hydrostatic equilibrium.
 
  • #8
However water moves to fill up empty spaces/air as there is no weight of liquid obstructing it , hence able to flow upwards to the tank?

Ahhh think that clears up for me, thanks guys!
 
  • #9
kakuta said:
What about water flowing from B to A seeing how the pressure at B is greater than at A

Yeah sorry I said that backward.
The inherent motion of the the water molecules in the cylinder is random. They can move from B to A but there is no "current" from higher to lower pressure in the cylinder.
 
  • #10
Thanks!
Another ques, if u guys don't mind,
Why don't we count in the liquid weight/phg when counting the pressure in a basic hydraulic system?
 
  • #11
I'm not sure what you mean when you say "count". The pg term in pgh is essentially the weight of liquid per unit volume, so it is counted in that way.
 
  • #12
Say in a hydraulic system, the pressure transmittted by a small cylinder is 50pa , hence 50pa is transmittted to the large cylinder. However there's a difference in height between the piston of small cylinder and the large cylinder,
The larger cylinder being at the shorter end.
In that case, why don't we add the pressure difference(counted using phg) + transmitted pressure onto the large piston?
 

1. What is pressure in a liquid?

Pressure in a liquid is the force exerted by the liquid on an object due to its weight and density. It is measured in units of force per unit area, such as pounds per square inch (psi) or pascals (Pa).

2. What is the difference in pressure between two points in a liquid?

The difference in pressure between two points in a liquid is known as the hydrostatic pressure. It is caused by the difference in depth and density between the two points.

3. How is pressure in a liquid calculated?

Pressure in a liquid can be calculated using the equation P = ρgh, where P is pressure, ρ is density, g is the acceleration due to gravity, and h is the depth of the liquid.

4. How does the difference in pressure between two points in a liquid affect the movement of the liquid?

The difference in pressure between two points in a liquid is responsible for the movement of the liquid. It causes the liquid to flow from areas of high pressure to areas of low pressure, creating currents and circulation.

5. What factors can affect the difference in pressure between two points in a liquid?

The difference in pressure between two points in a liquid can be affected by factors such as the depth and density of the liquid, the gravitational force, and the shape and size of the container holding the liquid.

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