The tag has no usage guidance.

learn more… | top users | synonyms

8
votes
2answers
10k views

Explanation that air drag is proportional to speed or square speed?

A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
6
votes
1answer
372 views

Height of Water 'Splashing'

Suppose from a height $H$, I throw a ball of mass $M$ and radius $R$ with initial velocity $u$ into a pool of depth $x$ having a liquid with density $\rho$ and coefficient of viscosity $\eta$. ...
3
votes
1answer
3k views

How to find out the maximum radius of a hole that can keep water stay in a container by water viscosity?

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 calculate the maximum radius of the hole that the water will still stay in ...
7
votes
3answers
1k views

How is viscosity described on the molecular level?

What is the 'molecular' origin of the viscosity? The molecular origin of elasticity is almost clear for me: at the very bottom the 'elasticity' comes from the attraction and repulsion between atoms ...
7
votes
1answer
3k views

Is there an analytical solution for fluid flow in a square duct?

I couldn't find one but assumed it must exist. Tried to find it on the back of an envelope, but got to an ugly differential equation I can't solve. I'm assuming a square duct of infinite length, ...
2
votes
1answer
2k views

What is the shear stress of a fluid?

One book defines the shear stress $\tau$ of a (Newtonian) fluid as $$\tau = \eta \frac{\partial v}{\partial r} $$ where $\eta$ is the viscosity. There is not much context, so I've made some guesses. ...
5
votes
1answer
325 views

Name of experiment

I'm seeking the name of or reference for an experiment I once saw in a college physics class. At the beginning of one class the instructor repeatedly wound a wiper that spread a blot of some type of ...
2
votes
1answer
957 views

Drag force at high speeds [duplicate]

The drag force on a spherical body according to Stokes' law is given by $$F = 6π\mu rv$$ Where $\mu$ is the dynamic viscosity of the fluid, $r$ is the radius of the spherical object, and $v$ is its ...
0
votes
1answer
703 views

Terminal velocity of a steel ball in water [closed]

I am investigating on the terminal velocity of steel balls moving in water. I used the balls with different diameters, such as 3.17mm, 6.02mm, etc. And I used a full-filled 1L graduated cylinder. I ...
1
vote
2answers
244 views

By what mechanism is lift produced on a rotating cylinder in an inviscid flow?

I am taking some introductory fluid dynamic classes, and have become very confused by the Kutta-Joukowski theorem. One of the conclusions that can be derived by applying Kutta-Joukowski is that a ...
7
votes
4answers
4k views

Does irrotational imply inviscid?

Let us consider a 2D irrotational flow, such that $\nabla\times\boldsymbol u =\boldsymbol 0$. Defining the stream function such that $\boldsymbol u =\nabla\times\psi \boldsymbol n$ where $\boldsymbol ...
5
votes
0answers
146 views

Gauge potential for locomotion at low Reynolds number

I've been studying some approaches with gauge theory to some problems in Mechanics and I've found the problem of self propulsion at low Reynolds number a quite complicated one. The approach I'm asking ...
4
votes
1answer
217 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
6
votes
1answer
698 views

Kinetic theory derivation of viscosity of a gas

Encountering a lot of issues trying to understand this. The basic idea of the derivation I'm using is as follows (the image here may help): I'm going to write $\langle u_x\rangle$ as the general ...
5
votes
2answers
322 views

What happened here in this Taylor-Couette Flow experiment?

I came across this video of Taylor-Couette Flow on YouTube. Originally I was looking for a visualization of the wavy Taylor vortices induced by the angular motion of the inner cylinder. However, I ...
5
votes
1answer
2k views

Are coffee's properties different enough from water's to cause increased spillage while walking?

I recently found this article, which describes how... It just so happens that the human stride has almost exactly the right frequency to drive the natural oscillations of coffee, when the fluid is ...
4
votes
1answer
338 views

How to write classical dynamics of solids in tensor form (relation of stiffness and viscosity tensor)?

This is a question about dynamics. If I have understood correctly there should be a tensor that describes the dynamics of a (solid?) body (= viscosity ?). I mean, tensor that includes the time ...
2
votes
1answer
78 views

Which formula is correct to find the terminal velocity of a sphere falling through a liquid?

Consider a sphere of radius $R$ & density $\rho_s$, falling through a liquid having density $\rho_l$, attains a constant terminal velocity $V_t$ then in this case the net force acting on the ...
0
votes
2answers
145 views

What is the reason behind Laminar Flow and the ability to return to near-original state in Laminar fluids?

Laminar flow here refers to the smooth disruption of fluid in layers, in a medium. A peculiar trait in a few examples of laminar flow is the ability to return to near-original state, as demonstrated ...
6
votes
1answer
217 views

Distance a curveball travels?

I've seen some discussions regarding the movement of a spinning object, say a curveball. However, all have been largely qualitative. I was wondering if anyone has seen or worked through a ...
3
votes
2answers
113 views

Lift and drag coefficients on other planets

The question I'm trying to answer seemed simple: how hard would it be to fly on a planet with lower gravity but also thinner atmosphere compared to Earth. If the answer could hint me at how much ...
2
votes
1answer
1k views

What is the buoyant and viscous force acting on a ball in free fall?

I was thinking about a situation were I have a long cylindrical jar with some viscous liquid in it. I also have a spherical ball with me. I drop the ball into the liquid inside the jar with some ...
1
vote
2answers
1k views

Is viscosity a function of density only?

I know viscosity is also a function of temperature, but (excluding superfluids) are there any fluids which are less viscous than fluids at lower densities? Is density the ultimate control on ...
1
vote
2answers
1k views

Gas viscosity at high pressure, high temperature

EDIT 1 PER COMMENTS I am wanting to model nitrogen gas viscosity as a function of pressure and temperature OR learn of an existing equation that models nitrogen viscosity for the pressure and ...
0
votes
1answer
42 views

Why does the stiffness of organic polymers (plastic) change so much with small changes in temperature?

This is on the borderline between Physics and Chemistry, but I would like a Physics perspective. I am guessing that plastics are a glass-like phase, rather than a true solid.
0
votes
1answer
178 views

Viscosity of water in the presence of solutes

Some physical properties of water change in the presence of solutes: vapor pressure, boiling point, freezing point and osmotic pressure. In particular, these four properties are called colligative ...