Hot answers tagged

3

Concerning your wording "force is transmitted (and maybe decreases because of loss of energy)" - no, no, the decrease of force is not easily connected to the loss of energy. Force can be decreased because there is friction, but this does not imply a loss of energy (not if nothing moves). And also energy can be lost (plastic deformation of the rope) without a ...


2

You have the right starting point with energy basically, but I'm finding your homework hint more useful than where you go from energy of a differential unit. It says "The energy density should be easy to identify." The energy density is: $$ \frac{\text{energy}}{\text{volume}} = \frac{\text{mass}}{\text{volume}} \frac{\text{energy}}{\text{mass}} = \rho ...


2

When the vapor pressure is equal to the external pressure, there will form a bubble. Not true. Instead, when the vapor pressure is equal to the external pressure, then any existing bubbles will begin growing continuously. And, if no bubbles are already present, then the water will superheat far above the boiling temperature, yet no bubbles will ...


2

While the answer of wbeaty is very interesting in showing points relevant in practice, I think all the answers are still missing an important and simple theoretical point, which you should consider to understand the process. vapour pressure does mean two different things as used above. First, the pressure, the existing water vapour would have (if it were ...


2

I think you are asking two questions. First : Can falling water create suction? The answer is Yes, but the effect is quite weak. It makes use of the siphon effect and is limited by atmospheric pressure, so the maximum column of water you could lift is about 10m. https://en.wikipedia.org/wiki/Siphon Second : Is it is possible to use this effect to ...


2

$Pressure = \dfrac{Force}{Area}$ Suppose your initial pressure is: $P_1=\dfrac{F_1}{A_1}$ Now you make the cross sectional area of the tube have $\dfrac{1}{4}$ the initial area. And this makes the total volume, hence total mass and total force $\dfrac{1}{4}$ what it was. The two $\dfrac{1}{4}$'s cancel. $P_2=\dfrac{(\dfrac{1}{4}F_1)}{(\dfrac{1}{4}A_1)} ...


2

I am not sure if the same laws apply to the heart as that of mechanical pump, but for a given flow rate, say X gallons per minute, the mechanical pump must develop a pressure P to overcome pipe friction and any other force trying to retard flow. If the pipe in a system is reduced in size, to pump the same flow rate a higher pressure will be required. The ...


2

As mentioned by @Chester, Bernoulli isn't a good approximation for viscous flows which blood flow is. Instead you should use the Hagen-Poiseuille law which relates the average volumetric flowrate and the pressure gradient in the pipe. From it we find that the flowrate $Q$ is proportional to: $$Q \propto R^4 \Gamma$$ where $R$ is the radius of the pipe and ...


1

Nondimensional groups such as the Reynolds number do not generally characterise the flow as a whole, but a feature that you choose in the flow. If the flow considered is not an academic problem, you will have several such features, which have different lengths, velocities... So there may be several different relevant Reynolds and Nusselt numbers in your ...


1

The following interpretations are taken from Thorne [2014]. Chapter 17, entitled Miller's Planet, discusses the issue of the large waves on the water planet in the movie Interstellar. There Kip mentions that the waves are due to tidal bore waves with height of ~1.2 km. In the appendix entitled Some Technical Notes, Kip estimates the density of Miller's ...


1

This got me thinking though, what would happen if the cross section does not change, and you have vertical flow of fluid in some pipe with an obvious change in elevation, but then had both the entrance and exit at atmospheric pressure. The energy equation, which is supposed to remain constant for a continuous fluid without losses, would have a differing ...


1

Your many questions shows remarkable effort on questioning. You seem to note the point. Does anydody could explain me what is the physical reason that the jet entrains air? "Diffusion" is now given as an answer. But If that would be true, a lot of air would be diffused also on the diesel stored in the tank. But there this doesn't happend in 10 years. ...


1

The Bernoulli equation is a good approximation only if viscous flow resistance is not important. In blood flow through arteries, veins and (particularly) capillaries, viscous flow resistance is very important.


1

Yes, the viscosity of a dilatant suspension will decrease if the viscosity of the solvent decreases. Surprisingly I struggled to find experimental data to back this up. Perhaps everyone thinks it's too obvious to be worth publishing. The best I could do is this school exeriment report. The authors timed the fall of a ball through the suspension, so lower ...


1

This is a really good question. What you are wondering about is why, when the cross section is constant, the Bernoulli equation doesn't predict free fall. It doesn't have anything to do with viscosity if the fluid is considered inviscid. The reason that the Bernoulli equation cannot be extended to the case of constant cross section is that the usual form ...


1

I've talken your diagram and attempted to draw on the grid lines for $Q = 2e$, $Q=3e$, etc: The problem is that the vertical spacing between the points is much smaller than $e$. If you were picking up ambient charge that charge would still have to increase in steps of $e$ and it isn't doing so. I would guess that your experimental errors are larger than ...



Only top voted, non community-wiki answers of a minimum length are eligible