Force per unit area.

learn more… | top users | synonyms

3
votes
2answers
112 views

Why don't we include $\rho g h$ in a hydraulic jack below?

Consider a hydraulic jack with massless pistons as follows. The famous equation for this system is $$ \frac{F_1}{A_1}=\frac{F_2}{A_2} $$ My question is why isn't the equation as follows? $$ ...
3
votes
3answers
414 views

Water Level and Pipe Widths

I ran into a bit of physics yesterday, and couldn't understand the physics at work. I've been scouring the Internet, but haven't found the answer yet. I'm guessing there's a basic principle I'm ...
3
votes
1answer
96 views

How does pressure relate to cosmological expansion?

In my cosmology class, we've been talking about pressure in the Friedmann Equation for acceleration: $$ \frac{\ddot{a}}{a}=-\frac{4 \pi G}{3} \left(\rho+\frac{3p}{c^2} \right) $$ In particular, I've ...
3
votes
1answer
238 views

Why was the conversion factor of the metric unit bar chosen the way it was?

The unit bar for pressure is clearly a metric unit, but its order of magnitude is a bit strange. In the centimeter–gram–second system of units we have: ...
3
votes
2answers
412 views

Pumping water from a closed column. Will the column get empty or just circualte?

As a picture is worth a thousand words, here is my problem: It is a closed water column with a bit of air in the top section. If I run the pump and make the water flow from IN to OUT, Will the ...
3
votes
1answer
342 views

Cosmology constant as a negative pressure?

It seems a positive cosmology constant behaves like a negative pressure. However, the positive cosmology constant cause a expanding universe. So I am puzzling about this: A negative pressure cause a ...
3
votes
1answer
287 views

Which heated, partially filled bottle will explode first?

This is in reference to a pasteurization discussion on a homebrewing forum. I have four closed bottles which will explode if containing too much pressure. Two of them are 50% full (A and B), and two ...
3
votes
1answer
511 views

Pascal law with two connected cylinders filled with water, and 50kg stones at both their ends

If I have two connected cylinders filled with water, and 50kg stones at both their ends (pressing both ends of the water) how much weight do I need to add on one side so that one of the stones reach ...
3
votes
1answer
461 views

What kind of curve would describe the rate of air coming out of a balloon?

If one graphed the volume per time of air being expelled from a common elastic balloon out of a hole of constant size relative to the balloon's surface area, would the curve of the graph be ...
3
votes
3answers
5k views

How does a pressure difference cause a force?

One more thing that's bothering me, could somebody clarify a little bit? I think it has something to do with being in the state of lowest energy state, what instigates that change? Perhaps even ...
3
votes
1answer
63 views

How do simple bird waterers work?

I made a simple bird waterer made from two 1.25L PET bottles. Let's call these two bottles the reservoir and the tray. Setup The tray is a bottle with the top cut off to leave only the bottom ...
3
votes
1answer
91 views

Inexplicable Results in a Vacuum Experiment

We've been doing the following experiment in our Physics Lab course and are coming up with some strange results which we're at a loss to explain. The purpose of the experiment is to determine the ...
3
votes
1answer
79 views

Pressure at a bend in a pipe

This is a question from a study guide for a military officer exam: I have fluid flowing through an elbow in a pipe (the elbow is in the shape of an upside down and backwards "J") and the flow goes ...
3
votes
1answer
81 views

Force to stop a moving rope vs. stagnation pressure of a fluid

Let $\lambda$ be a linear density of a rope which is moving into a scale at velocity v. The additional force on the scale due to the collision is given as $\frac{d p}{d t} = v\frac{d m}{d t} = ...
3
votes
1answer
102 views

Pressure difference between 2 side of wings of aircraft

I understand why the pressure is reduced above the wings of aircraft, but when I read books and look for information, it says that the air is compressed below the wings, I do not understand why it is? ...
3
votes
3answers
212 views

What exactly is “pressure”, and what's its relation to force?

I have looked around, and I will admit that I'm a bit lost on the definitions. Wikipedia's opening reads: Pressure (symbol: P or p) is the ratio of force to the area over which that force is ...
3
votes
1answer
784 views

Diffusion of gas in a liquid with changing pressure and solubility (chemical potential)

Modelling the diffusion of a gas dissolved in water in a vertical column of water, several meters deep. Also assuming the water is completely still, so only diffusion plays a role. (Actually a model ...
3
votes
3answers
3k 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
238 views

Deflection of a membrane

I am currently working on a project which is described as the deflection of a circular membrane. What I am trying to model is the deflection of a piece of plastic film (E=200MPa,v=0.5) when placed ...
3
votes
1answer
302 views

How should holes in a Tesla turbine look like?

I think of building a Tesla turbine out of old hard drives. Now I wonder how to cut ventilation holes in the platters. On the internet there are a lot of different attempts on that matter. A lot of ...
3
votes
4answers
538 views

Water to ice expansion in $1\textrm{mm}^3$ pit - pressure on the pit walls?

[EDITED] by mistake, the subject was regarding 1m^3 instead of 1mm^3. There should be a significant difference between the two... A 1x1x1mm pit filled with water is frozen at a slow rate (1K/minute). ...
3
votes
2answers
391 views

Burning alcohol vapor

Let's imagine a plastic container, sealed closed. We fill half of it with alcohol, then we generate a spark. The question is: can the mixture of alcohol and air burn, or do we need a hole to let air ...
3
votes
2answers
117 views

Dynamic water pressure from flow and diameter

I've to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but... I don't have. After Googling a lot, I found two formulas allowing to compute the ...
3
votes
0answers
55 views

How would water drain out of a sealed pipe?

While hiking through the Grand Canyon, I started wondering. Say we have a pipe for the purpose of transporting water across a canyon, with the bottom submerged in a pool of water. Like the blue line ...
3
votes
0answers
26 views

Is there a material with non-monotone density dependence on pressure?

Is there a material with such non-linear effects (including chemical reactions, phase transitions etc ...) so that there would be range where pressure increase would yield density decrease? What ...
3
votes
0answers
145 views

Second derivative of vapor pressure from a cubic equation of state

It is quite easy to compute the first derivative of vapor pressure with respect to temperature from a cubic equation of state at least at the critical point since there is a continuity with the ...
3
votes
0answers
54 views

Converting impact speed to pressure magnitude

In explosive safety and stability testing, a drop test is commonly used to determine the sensitivity to impact. In the test, an impactor of known mass is dropped. The initial height varies throughout ...
3
votes
0answers
160 views

Bubble in a pipeline

I am just thinking about this phenomenon: We have a horizontal pipeline with a flowing liquid, which contains a small bubble of gas. How do the dimensions of this bubble change when it reaches a ...
3
votes
2answers
120 views

How does a pierced vacuum move?

If a can of compressed air is pierced on the right, air pushes out, and the can moves to the left. If a vacuum container is pierced on the right, which way does it move? Right? Left? Not at all? ...
3
votes
1answer
128 views

Is this the correct way to I combine multiple interdependant pressure readings?

I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
2
votes
4answers
2k views

Balloons and lifting gases

Hydrogen is the lightest element, so it's cable of lifting the most weight in out atmosphere (probably not the best terminology there, but you get the picture) Would hot hydrogen (in the same sense ...
2
votes
2answers
27k views

Freezing point of water with respect to pressure.

I know when the pressure is reduced, the boiling point of water is reduced as well. But how does the pressure affect the freezing point of water ? In a low pressure environment is the freezing point ...
2
votes
2answers
3k views

How can I calculate the pressure against the sides of a container? [closed]

While answering this question on DIY.SE, I wanted to calculate the amount of pressure (in psi) that would be exerted on the walls of the container. However, I don't know much about how to calculate ...
2
votes
2answers
219 views

Why is a hole in a ball?

I wanted to know why there is a hole in the ball (basketball, volleyball, handball) to fill the ball with air. Why can't the ball come with filled in air and fully sealed so that there is no loss of ...
2
votes
4answers
768 views

Why does sound need air in order to travel?

I know that in space, because of vacuum that we can't hear voices or sound to be specific, why is that? Why does sound need a medium to go through?
2
votes
2answers
105 views

Do we hear sounds differently on the highest mountains?

Some searching gives that above 6,000 meter altitude the air density is less than half of that at sea level. Speed of sound is about 15-20% slower and "acoustic impedance" seems to change too. Do ...
2
votes
2answers
2k views

How can sound waves propagate through air?

We know that the sound waves propagate through air, and it can't travel through vacuum. so the thing that help it doing that is the air's molecules pressure. So my question how can that happens? I ...
2
votes
1answer
182 views

Is there a way to measure atmosperic pressure without an instrument?

Just that . I am not too much concerned about the accuracy of measurements .
2
votes
3answers
203 views

Making a “heavier-than-air” craft float

How big would a hollow rigid object need to be to float, (not in water but in air) if all of the air was vacuumed out and the container sealed?
2
votes
2answers
114 views

How much pressure does the earth's central atom experience?

If mass is distributed evenly about it: "central atom", then it should be weightless right? If reasonably so, does it still experience the pressure? I would like to calculate, but I'm not so ...
2
votes
4answers
86 views

Mathematical Reasoning for Fluid Pressure as a Scalar

This question from a while ago and answers/comments to this question from earlier today both make heavy mention of the fact that fluid pressure is a scalar. Although this information was surprising ...
2
votes
2answers
145 views

Magdeburg Hemispheres

The Magdeburg Hemisphere experiment was the experiment that showed the effect of pressure differences on a vacuumed sphere. We know that the Force caused by pressure is $\Delta p A$ and so you can ...
2
votes
2answers
4k views

Pressure at a given altitude?

I am trying to find out the pressure at a given altitude but have been disappointed to find the following equation does not work at all: (h = height in meters) Where sea level standard ...
2
votes
1answer
44 views

What is the maximum height for a puddle of water, assuming stp?

I wonder if anyone has figured this out. Assuming, standard temperature and pressure(273 K and 1atm), what is the maximum height of a water puddle on a flat surface? There might be some other factors ...
2
votes
1answer
61 views

If a window in a plane cabin breaks will a bunch of water vapor form?

If a plane has some windows broken mid-flight (ie open) will the plane suddenly be full of water vapor because of the difference of pressure?
2
votes
1answer
99 views

Where does the steam pressure go?

Lets say you build a steam boiler and then you connect several turbines to the boiler in series. What limits the number of turbines that you can connect to the boiler in this way? In my mind, it ...
2
votes
3answers
100 views

How does pressure factor into mechanics?

We just started learning about pressure in our school, and i am a bit confused. I tried to google extensively, but i didn't really find much. In mechanics, so far in our school we've been taught ...
2
votes
1answer
166 views

Thermodynamics, PV diagrams?

My teacher told me that the total amount of work done on or by a gas can be represented by the area enclosed in the process in a PV diagram. This is only valid for non isothermic processes, right?
2
votes
1answer
810 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
306 views

Difference between Diamond anvil cell and Bridgman cell

In high pressure physics what is the difference between diamond anvil cells (DAC) and Bridgman cells? My understanding is that they are both forms of anvil cell but in the scientific literature I'm ...