# Tag Info

19

That is simply convection. The wick does suck molten wax, and it goes up by capillary to the middle of the flame, but that movement is way to slow to explain the fast particles in your video. Moreover they are moving in the opposite direction! Convection happens because the wick is hot, and it makes the wax around also hot, so the wax expands a little and ...

4

As Thomas has commented, the trick is that we only assume first order terms and this convective acceleration would be small of the second order. In fact, that is one of the first assumptions to drop when you consider more general cases. See e.g. Burger's equation for first generalizations and/or Lighthill's equation for source terms arising in the wave ...

3

To derive the Bernoulli equation for inviscid fluids, the plan is to rewrite the Euler equation in such a way that we have gradients. I'll write the Euler equation with gravity here $$\frac{\partial \vec{u}}{\partial t} + \vec{u} \cdot \vec{\nabla} \vec{u} = -\frac{1}{\rho} \vec{\nabla} p + \vec{g}.$$ Recall $g = - \vec{\nabla} \Psi$, and \$\vec{u} \cdot ...

2

Reduction of surface tension of water can be done in several ways> A few of them are as follows: Surfactants are compounds that lower the surface tension of a liquid like water, the interfacial tension between two liquids, or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. ...

2

Assuming: the balloons are all of equal volume and are all filled with the same gas We can conclude: the end with two balloons has a greater buoyant force and will rise. If the end with a single ballon is in air and the other end in water: the buoyant force depends on the weight of displaced fluid, so the buoyant force is greater on each of the ...

2

Tried to comment on question, need 50 rep. (why??) I believe what you are referring to is viscosity in laminar flow. If I recall correctly, non-laminar flow is a precondition for turbulence, but I believe you can have viscosity which is not turbulent. Is this the direction you had in mind? EDIT: Fluid molecules far away from the object will feel ...

1

The assumption when linearizing is that the deviations/perturbations are very small compared to the reference (averaged) values. Typically the derivatives of the deviations are of the same order as the deviations themselves. Consider the deviations having this functional form in 1D: $$u'=\Delta u\sin kx\quad \partial_x u'=k\Delta u\cos kx$$ The deviation ...

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