Force per unit area.

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17
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4answers
2k views

How is hydrostatic pressure overcome when a star is formed?

If stars are formed by the collapse of dust clouds under gravity, how is the pressure of the dust cloud overcome? As more material gathers together, gravity will increase, but pressure will also ...
12
votes
5answers
12k views

Why does my door shut faster when the window is open?

I've noticed that if I shut my door when the window is open in a room, the door will tend to shut faster. If I shut the door when the window is closed with a normal force it will not fully close as if ...
13
votes
4answers
257 views

How quickly should a fluid come to hydrostatic equilibrium?

Let's say I'm holding a one-liter water bottle, full of water, which I then drop. Before dropping the water bottle, the equilibrium is for there to be a pressure gradient in the water canceling the ...
10
votes
5answers
10k views

What about negative Pressure?

Here is something I see : Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
6
votes
2answers
1k views

Hydrostatic pressure on a teapot spout

The phenomenon where water flows on the outside side of a teapot spout is named "The teapot effect", and occurs due to a difference in pressure between water and the atmosphere. Consider the image of ...
15
votes
4answers
3k views

Why do bubbles make a sound?

I have an understanding of how bubbles work. They encapsulate air (or other fluids) in a membrane caused by surface tension. When they pop, there is often a sound. Sound is a type of energy, kinetic ...
9
votes
1answer
279 views

What happened to this folded paper in a hydraulic press?

The video below apparently shows a man folding an A3 size piece of paper 7 times, putting it under the hydraulic press each time. After 7 folds, on the last press, the paper sort of explodes. What's ...
9
votes
3answers
13k views

Why does the water level equalize in a series of tubes?

Say I have a series of tubes (not the internet) looking like this, where w represents water: ...
5
votes
1answer
596 views

Bowling Ball Sinking Rate - Variable or Constant?

In today's (Jan. 16, 2014) xkcd What If?, Randall Munroe discusses how fast a bowling ball will sink to the bottom of the Mariana Trench. He calculates the drag on the ball, and then plugging in the ...
4
votes
3answers
8k views

Why should fluids be confined for Pascal's Law to be applicable

When is Pascal's law about fluid pressure propagation applicable? Is it applicable to a closed circular pipe with a pump rotating the fluid, but not to a tub of water. Most statements require only ...
3
votes
1answer
403 views

Why does the bubbling of a soda bottle pulsate?

If I take a bottle of carbonated water and open the cap slightly to allow the gas to escape, there will be a sudden rush of bubbles foaming to the top of the liquid for a few seconds, then a partial ...
0
votes
1answer
85 views

Properties of Fluids-theoritical confusion

I am having a very basic confusion on how we calculate the height of atmosphere when we assume that the density does not change with altitude(density remains 1.29 kg/m$^3$). I want to know why we say ...
0
votes
2answers
16k views

Why do particles in high pressure air always flow to lower pressure?

The title really says it all: Why is this case? A "Feynman type" answer would be really appreciated as I'm more of a layman that a physicist.
9
votes
4answers
6k views

Effect of water pressure on sinking objects

As I understand, water pressure increases as we go towards bottom of the ocean. So if an object* is thrown into water and it starts sinking with some speed, does the sinking object's acceleration ...
8
votes
4answers
4k views

Water pressure in free fall

The increasing water pressure as you go deeper is generally explained in terms of the weight of the water column above the observation point pressing down. The question, then, is what would happen if ...
8
votes
3answers
2k views

Trying to understand jet engine [closed]

I'm trying to understand at a high level how a jet engine works. I want to know if the following summary I wrote is more or less accurate: The jet compresses regular air into a combustion chamber. ...
8
votes
1answer
1k views

Ping-pong ball pontoon

Imagine a vertical pipe (both ends opened) in the water. Drop several ping-pong balls into pipe and cover them with a cylinder. When you have enough balls, the cylinder will float. Now start adding ...
8
votes
3answers
2k views

Why can, or can not, a perfectly incompressible fluid exist?

Water is normally assumed to be an incompressible fluid - for example in the context of calculations involving water pressure. I wondered whether that is strictly true, or an approximation? Later I ...
7
votes
1answer
1k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
6
votes
3answers
9k views

What is the relation of sound propagation to air pressure?

I am wondering, air makes sound propagate. So in a vacuum there is no sound, but what is the relation of pressure to sound volume? Is it linear? If I have a source of sound and let's say I am in a ...
6
votes
3answers
1k views

The physics behind Balloons lifting objects?

Apologies for the super basic question, but we all have to start somewhere right? Can somebody please explain exactly how you would calculate the number of helium balloons it would take to lift an ...
4
votes
2answers
1k views

If I put a ping pong ball in a vacuum, would it pop?

If I put a ping pong ball in a vacuum, would it pop? If so, at what point would it happen? Any standard table ping pong ball is acceptable.
4
votes
2answers
518 views

How to calculate the highest theoretical artificial hill?

The biggest peak in the world is Mount Everest. Imagine someone starting to make an artificial hill (like pyramide) from soil (earth). So, when starting with an 200x200 Km base area, with 45degree ...
4
votes
3answers
3k views

Why is there a 90˚ phase angle between particle velocity and sound pressure in spherical waves?

My text says that in a plane sound wave (or in the far field), particle velocity and pressure is in phase. As we move closer to the sound source (to near field and more spherical waves), the phase ...
4
votes
4answers
6k views

Dyson Air Blade as a propulsion system?

I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, ...
4
votes
6answers
5k views

What is Pressure Energy?

While deriving Bernoulli's Theorem, our teacher said that the sum of KE, PE and Pressure Energy per unit volume remains constant at any two points. $$P + \rho g h + \frac{\rho v^2}{2} = \text{...
4
votes
1answer
143 views

How much atmospheric pressure (CO2) is required to carry iron oxide dust in the wind?

It is common knowledge that there are dust devils and dust storms on Mars. But can we demonstrate that the atmospheric pressure on Mars, which is 0.6% of the pressure we experience on Earth, provides ...
3
votes
1answer
856 views

Why is the dynamic pressure not a vector quantity? [duplicate]

I understand that static pressure is a scalar quantity as it acts equally in all directions, then by the same reasoning dynamic pressure should be a vector quantity as it only can be measured by ...
3
votes
4answers
8k views

Calculate water flow rate through orifice

I'm not very good with fluid physics, and need some help. Imagine the following setup with water contained in-front of a wall with an opening on the bottom: How do I calculate the water flow $Q$?. ...
2
votes
2answers
144 views

How does force transmit through a solid block?

If you take a solid block, say, a cube of side length $l$ with density $\rho$, you place it upon a solid floor, and you apply an external pressure of $p(x,y)$ on the upper face ($x$ and $y$ define a ...
2
votes
1answer
2k views

Heat of vaporization of water - dependence on relative humidity?

Does the heat of vaporization of water depend strongly on the relative humidity of the gas into which it evaporates? Some context: If we want to calculate the dew point of water, we find the ...
2
votes
2answers
342 views

Existence of gusts of wind, an anomaly?

Enthusiast + Student, not a pro, so pardon my ignorance. How can wind possibly flow in gusts? The way I understand it, a gust is a pocket of air which hits you at slightly higher speed. But how ...
1
vote
2answers
1k views

Water pressure on slanted wall

Water pressure is simply $pgh/2$ for a vertical wall parallel to the depth of the water at exactly the half the water's depth. Suppose the wall is tapered (angled) slightly at around 2 degrees from ...
1
vote
1answer
247 views

How does pressure influence temperature in liquids?

Lets say we have a tank with a fixed mass of liquid at atmospheric pressure and room temperature. How do we influence the temperature when we exert pressure (e. g., with a piston) on the liquid? Are ...
1
vote
1answer
120 views

Pressure coefficient on fluid mechanics

I have to solve numerically a fluid mechanics problem. I have an airfoil with a flap deployed downwards, under the airfoil I have set a mesh with some nodes. I have already computed stream function ...
1
vote
2answers
185 views

Negative pressure

How is negative pressure created in a fluid system?Isn't it counter intuitive that we are reducing the pressure of a system containing no molecules(zero pressure) to a lower value?
1
vote
1answer
2k views

water fountain with a pipette

if you get some hot water in a pipette an put the pick of it on the top the water will jump out f pipette and make a fountain.I wondered if any one could tell me what is the reason?
0
votes
2answers
398 views

What is the pressure of falling water?

Imagine a breaking wave 10m high. The wave breaks onto a beach. What is the maximum pressure created by the wave on the beach, ignoring effects such as might be cause by air?
0
votes
1answer
23k views

To calculate pressure at point in a vertical water pipe of given diameter

Is it possible to calculate pressure at a point in a pipe, where a solenoid valve shall be placed, given that the pipe carries water (utility supplied, regular water) from an overhead tank (at a ...
8
votes
2answers
959 views

Why water in the sink follow a curved path?

When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity.. Why this phenomena ...
8
votes
4answers
3k views

Is there a depth at which a human body, with lungs full of air, will no longer float?

I was watching a special on divers who dove down hundreds of feet without tanks or gear. The show referred to a depth at which the diver was no longer buoyant and would actually sink, even with lungs ...
6
votes
6answers
21k views

Why does a gas inside a closed container experience atmosperic pressure when the gas itself is not in contact with the atmosphere?

I know this is a very basic (and probably stupid) question, but I have been confused about this for a long time.
5
votes
3answers
837 views

A book sits on a table. What is the net force of air pressure?

An elementary problem asks, A book is at rest on a table top. In what direction is the net force of air pressure on the book? Is this a meaningful question, and if so, what's the answer? If ...
4
votes
2answers
4k views

How deep in the ocean can a ping-pong ball go before it collapses due to pressure?

Stimulated by the calculation showing that a ping-pong ball does not pop in vacuum, I'm driven to ask how deep in the ocean a ping-pong ball can be brought before it collapses due to pressure. This ...
3
votes
2answers
224 views

Why doesn't water in water barometer boil?

I have read that the pressure in a water barometer at the top of the water column is around 0.5 psi and at such low pressures water should boil at around ~26°C (Room temperature). [1] [2] How ...
3
votes
1answer
2k views

Why doesn't soda fizz at high pressure?

In this video, a can of soda is opened in an underwater station at 2.5 atm. The demonstration is that shaking the soda doesn't cause it to explode like it would at normal pressures. Why does this ...
3
votes
2answers
399 views

Pressure Inside an Ideal Gas

A non-relativistic ideal gas exerts a pressure at the surface of its container $p = \frac13 \rho \langle v^2 \rangle$ where $\rho$ is the mass density of the gas and $\langle v^2 \rangle$ is the ...
3
votes
5answers
17k views

What is the effect of an increase in pressure on latent heat of vaporization?

What is latent heat of vaporization ($L_v$) in the first place? Wikipedia seems to indicate that it is the energy used in overcoming intermolecular interactions, without taking into account at all any ...
2
votes
1answer
1k views

Drinking juice through a straw

Why we are able to suck more drink through a larger diameter straw than a smaller diameter straw if $p_1 v_1 = p_2 v_2 = Q$ as per Bernoulli's Principle. The pressure difference I create in mouth ...
2
votes
1answer
10k views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...