# Tagged Questions

The quantitative study of how fluids (gases and liquids) move.

568 views

### Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
36 views

### Entropy and vacuums

If I have a vacuum (completely devoid of any particles; Q.M. effects aside), then turn a nozzle and let a gas freely expand into the vacuum, will I have increased the entropy of the vacuum? I get ...
28 views

### Is drag force in the direction of particle motion or opposite to motion?

Suppose water is flowing in horizontal direction (positive $x$-direction) and a particle immersed in that water is also moving in the same direction. In this case, is the drag force $F_D$ in the ...
30 views

### effect of opening the barrier between a tube with one side pressurized and the other side a vacuum

What would happen when a tube with an air space pressurized to 500 atm by the water exerted at 5 km below the surface was opened into a vacuum chamber rising up 5 km to the surface? The bottom of the ...
135 views

### What is the total velocity/force on a particle in fluid?

I am now facing a fluid-particle interaction problem. I would like to simulate particle motion in a fluid. I do know the external force acting on a particle (dielectrophoretic force in this case) ...
25 views

### Trouble understanding a formula in Turbulence

I'm very new to turbulence.I'm reading this book on "Turbulence: An introduction for scientist and Engineers" by Davidson. I came across this formula for energy dissipation. This is in chapter one. I ...
27 views

### Bent capillary tube

What would happen if I bend a capillary tube and use it as shown in figure? 1.Will the water(or any other adhesive liquid) level remain same as before bending? 2.or it will come up till end? 3.Or ...
304 views

### Fluid dynamics tsunami

I have been given a energy head (pressure) in meters for a given tsunami on land. If the tsunami hits a wall 1 meter by 1 meter, is it possible to calculate the height it will reach. I am thinking it ...
48 views

### Physics behind blowing soap bubbles

Is it possible, using the surface tension of a soap bubble, to calculate the maximum pressure (created by the air flow) it can withstand while still attached to the orifice to prevent it from ...
19 views

### How does one compute the maximum height reached by the water droplets in this experiment and what is the theory behind such phenomenon? [on hold]

Hot Water Fountain - Partially fill a Mohr pipette with hot water. Cover the top of the pipette with your thumb. Turn the tip upwards and observe the fountain exiting the tip. Investigate the ...
80 views

### Physical explanation of Pascal’s Law

I have a problem with physical explanation of Pascal’s Law. For example, when I was teaching my sister (a high school student) about force transmitting by a rope, I said her: “In a very simplified ...
358 views

### Bernoulli's Equation for flow of gas and changing area

My task is to determine the size of piping needed in a system. In this system, hydrogen gas flows horizontally in a $\frac{3}{4}\,\mathrm{inch}$ pipe and into a vertical pipe of a larger diameter. My ...
23 views

### Probability of Millikan's drop gaining or losing charge during the experiment

I performed Millikan's experiment with latex drops. I did not get the "step graph" that I wanted (though the precision of the experiment was really bad as seen in the figure). My first drop is ...
29 views

### Fluid Mechanics: Stream Function for Axisymmetric flow

I have problem in understanding the result of stream function in Axisymmetric 3D flow: I know that the result is (for spherical coordinates): ...
217 views

### How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
28 views

### Why use a LED light source in an experiment of fluid mechanics?

There are two main kinds of light sources used in the experiments: Laser and LED, which are very different in energy consumption as well as the wavelength range. I guess the reason is related the ...
28 views

### Would it be possible to kill a flea or mosquito with a high probability using high pressure and low volume? [on hold]

I was thinking about how to kill off some bugs in the house and it dawned on me that part of the ritual of spraying down insects is the spray itself - they don't seem to handle the pressure well, and ...
212 views

### What is the real cause of the boiling (forming of bubbles) of water?

I've got a question about the boiling of water. I'm a first year physics student and from the Netherlands. I've searched alot about the boiling of water and this confused me. Everyone said something ...
181 views

### Navier-Stokes Energy Equation

I've been assigned (for homework in a mathematical modelling course) the task of deriving the Navier-Stokes energy equation in one space dimension: Consider a fluid flowing through a cylindrical ...
30 views

### Hourglass fluid mechanics issue with Bernoulli's equation

I know that I'm thinking about this problem wrong, but I've been pondering it for a while and can't understand something. On my fluid mech. exam I had a problem that asked to determine the radius of ...
18 views

### How would an increase in temperature affect ooblek's (non newtonian fluid) viscosity?

Due to the fact that Ooblek (cornstarch and water), contains so much water and from what I understand it is non newtonian due to the particles suspended in it, would it therefore be correct to say ...
33 views

### can water falling/running down in pipe cause suction capable of creating a continuous flow

can water falling under gravity create suction force and if so, how much force..if i put a huge strong tank on top of a hill and on top there is a tap connected to a huge body, then i put a another ...
63 views

### What is the equation of state for a relativistic fluid/gas? [closed]

say we have a relativistic fluid/gas. now let us write: $e$ - energy density in the fluid's rest frame. $P$ - pressure in the fluid's rest frame. $n$ - number density in the fluid's rest frame. ...
47 views

### Determination of resultant force

As we know, force is product of pressure and area as below:$$d\vec{F}=Pd\vec{A}$$ P is a scalar and orientations of the small force and small area are same. I have three questions (they are ...
74 views

### Ball Rotating in Place Under Waterfall

https://www.youtube.com/watch?v=Khf6koh3IO8 Can anyone help me explain this? It seems like the ball should shoot out from underneath. I have two main theories. 1) Bernoulli's Principle says that the ...
182 views

### Bernoulli Equation for isentropic ideal gas flow

If one derives the Bernoulli Equation for the isentropic ideal gas flow you get: $$\frac{1}{2}v^2 + g z + \left(\frac{\kappa}{\kappa -1} \right) \frac{p}{\rho} = const.$$ Two questions: Is ...
46 views

### A question about droplets formation

This picture shows a fuel ejector of a diesel engine that propels ships. When the fuel line pressure exceeds 380 bars, the tension of the spring is overcomed and fuel is ejected into the combustion ...
254 views

### Maximum hole size to stop a fluid passing through a solid

In a previous question, the following is answered in a general sense: Assume I have a inverse cone which holds 200ml water. I am going to cut the tip of the cone to create a small hole. How to ...
35 views

### How to stop water flow in a siphon?

I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it ...
284 views

### Explanation of the waves on the water planet in the movie Interstellar?

We will ignore some of the more obvious issues with the movie and assume all other things are consistent to have fun with some of these questions. Simple [hopefully] Pre-questions: 1) If the water ...
31 views

### how to choose characteristic length in reynolds number [duplicate]

now reynolds number for a system is defined as follows $$Re=\frac{\rho*u*L}{\mu}$$ where $L$ is the characteristic length. I am wondering how this $L$ is decided (in case of flat plate it is $x$ ...
19 views

### Approximating the pressure drop for a centrifugal fan/blower

Is it possible to approximate the pressure drop for a centrifugal fan by using the fan's characteristics, the airflow, and the speed at which the fluid is being ejected? Would it be possible to adapt ...
112 views

### Can the Arcaboard fly?

Recently, BBC news had a video that claimed to show a "real" hoverboard: As far as I can tell, there are 36 small fans on this device, and it seems to be flying just a few inches off the ground. ...
16 views

### Convective heat transfer coefficients - how do you calculate them?

How do you calculate (or otherwise determine) h_i and h_o (convective heat transfer coefficients) for a heat exchanger? Standard thermodynamics equation below for reference. My specific situation ...
40 views

### Do you need to increase pressure to pump a fluid from a large pipe through a small pipe?

The application of this question is towards clogged arteries and blood flow. I am wondering why people with clogged arteries have high blood pressure if a smaller artery (assuming it is smooth and ...
2k views

### Pressure change with a pipe diameter change

I have a question regarding a water line from the street to a house. What happens to the pressure in a water line if it goes from a 1" diameter pipe (at street) and increases to a 1.5" diameter pipe ...
32 views

### Symmetrical rising of dust [closed]

What is the most symmetrical way in which a cloud of dust, say from a carpet or any other dusty object can rise? Does it maybe rise on the shape of a funnel? A mushroom cloud perhaps? The shape of ...
11 views

### Calculating Pressure in Lattice Boltzman Equation

I'm new to the LBE, but have been finding them very helpful for doing some fluid dynamics simulations. I was wondering how pressure would be calculated. I'm guessing this is quite easy, but it's ...
56 views

### Why jets entrain mass?

This very beautiful picture shows a jet of fuel in the combustion chamber of a diesel engine. Does anydody could explain me what is the physical reason that the jet entrains air? Why jets and plumes ...
56 views

### velocity of water exiting a 20 m hole at the bottom of water column 5000 m in height

What would be the velocity of water exiting a tube that has a height of 5000 m from a hole with a diameter of 20 m at the bottom, if the height of the water remains constant at 5000 m? Would it be ...
14 views

### Inertial force of fluids [duplicate]

Reynold's number is the ratio of inertial force to viscous force.I also know the definition of inertial force.but where does a fluid get this force from?what are the factors responsible for this ...
30 views

### Equations describing a counterflow heat exchanger [closed]

One of my experiments has a water-cooled apparatus. I plan on building a heat exchanger to keep the apparatus cool. However, I am not very good at thermodynamics and could use a hand. Also, from a ...
20 views

### Which direction does the air/fluid move in each segment? [closed]

1) I have this circular tube, assume its frictionless. There are 8 valves that suck (red) or add (green) the fluid/air. Assume that we always balance the valves such that the sum of pressure change ...
24 views

### Force Balance Question [closed]

Hello, I've been asked to show that: $$d\Gamma=\tau 2\pi r^2 dr$$ Where $\Gamma$ is the torque applied to the shaft and $\tau$ is the shear stress of the sample fluid at radius $dr$. So, I know ...
36 views

### What is the psi at the bottom of different tubes filled with water filled at the same height

if I have a 1 inch square tube with 144 feet of water I know I have about 63 pounds of water (63lbs ft**3) and 63 psi at the bottoms off the tube. If I have a 1/4 inch sq tube filled with water at ...
66 views

### Fluid Mechanics Paradox

This is a deceptively simple problem in fluid mechanics that I can't quite figure out because it produces a paradox. Suppose that there is a straw and a small column of water inside the straw, such ...
3k views

### Mechanics around a rail tank wagon

Some time ago I came across a problem which might be of interest to the physics.se, I think. The problem sounds like a homework problem, but I think it is not trivial (i am still thinking about it): ...
53 views

### Submerged water jet

I am trying to calculate at what pressure and speed water from a high pressure water jet will hit an object 100 millimeters away from the nozzle opening, but i can't figure it out. The nozzle will ...