# What is Liquid pressure: Definition and 24 Discussions

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled gage pressure) is the pressure relative to the ambient pressure.
Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m2); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

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1. ### Solving the Problem of Capillary Action in Tiny Peristaltic Pumps

Hello, I designed a tiny peristaltic pump which works really fine. I am using a very thin tubing of 0.5mm diameter, which makes me struggle with capillary action, unfortunately. When my pump is not working, sometimes liquid still flows into the tubing because of capillary action. Do you have...
2. ### Problem understanding liquid pressure

Good morning. I joined this forum to improve my self and give back what i will learn here for the members of this forum. I m confused about the notion of pressure and i will explain the point that i don't understand. since we know that the pressure is the force over surace. and since we know...
3. ### Force of water against a dam gate

Question : I start by putting the image of the problem from the book. The water surface is given to run along the (top) edge of the bridge. Attempt : The crux of this problem lies in the fact that the pressure of water against the gate will vary along its depth ##h## as ##\rho gh##. This makes...
4. ### Keep working on the liquid pressure problem

Without calculating the friction, if the force of gravity on the piston, the initial force F on the piston S is what? 1. F=-ρgSH; 2. F=-（1/2）ρgSH; 3. F=0; 4. Other. I'm not sure which is the correct result, can someone help me analyze it again?
5. ### Is Pressure Constant in U-Tube Arms with Different Density Liquids?

A liquid in a U-tube maintains the same level in both the arms. When another liquid which does not mix with the first one is poured in it, the air interface with either of the liquids in both the arms will be at different levels. Considering a point at the top surface of liquid A, the pressure...
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### Calculating Liquid Pressure: Water and Mercury

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Notes: Water density = 1000 kg/m3 Mercury density = 13600 kg/m3 g = 10 N/kg Hi all, please help on this questions. The attempt from me a) (0.7m)(1000kg/m3)(g) = (h)(13600kg/m3)(g) h = 0.0514m h...
7. K

### How does the capillary tube in refrigerators work?

How does the capillary tube decrease the pressure on the liquid when its diameter is smaller? How small diameter of capillary tube is helpful in causing more pressure drop? And how, when pressure drops, the liquid instantly cools down?
8. ### Understanding Liquid Pressure in a Cone: How Does It Compare to a Cylinder?

I am confused about the pressure depending only on the depth of the liquid, particularly for a cone. Up until P=mg/A=ρVg/A I understand it, but the problem I have is cancelling the area with the volume to give the height. How does this work when the volume of the liquid in the cone is not given...
9. ### How is blood pressure in our body constant?

Generally pressure in a liquid changes with height at which we measure. But still blood pressure remains almost same throughout the body. How is this possible?
10. ### Air Pressure vs Liquid Pressure

Okay, so I am looking at this article (link at bottom) and it says they have a microorganism liquid contained inside of a CLOSED steel pipe fitting and they heat it until it's reached about 570 degrees inside. SO HOW MUCH PRESSURE GROWS INSIDE THE CLOSED CONTAINER? As far as a real life...
11. ### Liquid pressure in a closed system

Homework Statement A steel cylinder filled with water contains 3000psi of pressure, completely sealed, walls ≈ infinite thick. No gas is present inside of the cylinder, and no heat exchange. To the problem; if a solid rod/piston enters on top of the cylinder with no possibilities to bleeding...
12. ### Liquid pressure gradient in zero gravity

Is there any data about such measurements? I think, there has to be a pressure gradient in a floating liquid sphere due to surface tension.
13. ### Liquid pressure in microgravity

Homework Statement This is more of a conceptual question rather than a homework problem. This is my first post, so apologies if this is in the wrong section. Consider a jar full of liquid in microgravity. My book says: According to the formula p = ρgh, p→0 as g→0. Thus there is no...
14. ### Why does water pressure remain constant when a cube is inserted into it?

i have been studying pressure and hydrostatics and i stumbled upon this now imagine a container filled with water , and there is a cube in the water now i know that the weight of the displaced water = the upthrust force but what bothers me is , how is the water pressure at a certain level...
15. ### How liquid pressure = dgh can be generalized

I've seen the standard derivation of the expression for liquid pressure P = dgh where, d = density of the liquid; g = acceleration due to gravity; h = height of liquid column in many textbooks has been done by using a specific example of a cylindrical vessel. In such a case, the geometry of the...
16. ### Pressure inside a bladder when subjected to an outside liquid pressure

If I have a bladder (or balloon) that is charged with 300# of a nitrogen gas at a normal atmospheric pressure outside the bladder, and I then enclose the bladder and subject that bladder to a liquid pressure of 25# on it's outside surface area but inside the enclosure. Assuming a constant...
17. ### What is the derivation for the equation for liquid pressure at depth?

The pressure of a liquid of constant density at depth 'h' is given by the equation: P = hρg I am trying to understand the derivation of this equation. I understand it perfectly for liquid columns with rectangular liquid columns but I can't see why it works if the shape of the fluid...
18. ### Pressure Difference in Tank with/without Wooden Box

if in a tank full of water big a wooden box floats on water then will the pressure below the box in the liquid be different from , the case , when there would be no wooden box ??
19. ### Liquid Pressure: How Does It Exert Pressure?

how does liquid exert pressure in all directions? When a liquid is placed in a container, i understand that it exerts pressure on the bottom of the container due to its weight but why does it exert pressure on the sides of the container? is that due to the fact that the molecules in liquid are...
20. ### Visualizing Liquid Pressure: A Diagrammatic Guide

The forces of a liquid pressing against a surface add up to a net force that is perpendicular to the surface. I cannot visualize this. Could someone help me out diagrammatically here?
21. ### Vapor pressure vs liquid pressure in enthelpic combustion reaction

Homework Statement Hi guys, I'm a little lost on what should probably be a simple question Using the following combustion reaction (C7O2H6)s + 7.5 (O2)g --> 7 (CO2)g + 3 (H2O)l the equation indicates that water produed by the reaction is liquid water not water vapor. Is this correct...
22. ### Liquid pressure multiple choice

Homework Statement a piece of metal of 10cm X 20 cm X 5 cm is sitting flat on the bottom of water basket, with one of the 10cm X 20cm sides facing up. the metal has density of 19.3 g/cm3. The basket is filled with water(full). The backet has a radius of 0.25m and a hight of 1m, density of...
23. ### Liquid pressure and circular motion

A tube is sealed at both ends and contains a 0.0212-m-long portion of liquid. The length of the tube is large compared to 0.0212 m. There is no air in the tube, and the vapor in the space above the liquid may be ignored. The tube is whirled around in a horizontal circle at a constant angular...
24. ### Constant liquid pressure device

I was wondering if anyone could point me towards a source about making constant head devices. I was wanting to measure and then relate, experimentally, the velocity of a stream to its cross-sectional area. Since this will be done mostly at home using pedestrian tools, I need to find out how I...