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Jan
20
comment Momentum of slowly spinning (viscous) fluid
I agree, it is very tricky to marry the boundary conditions to the solution.
Jan
20
comment Momentum of slowly spinning (viscous) fluid
With a cursory look it does not seem this meets the natural boundary conditions of $v_\theta(r=0,t)=0$ and $v_\theta(r=R,t)=\Omega R$. Also the initial conditions are $v_\theta(r<R,0)=0$ I think.
Jan
20
revised Momentum of slowly spinning (viscous) fluid
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Jan
19
revised energy of a ball
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Jan
18
revised Momentum of slowly spinning (viscous) fluid
edited title
Jan
17
comment Four momentum in particle physics
With the second definition the units are correct.
Jan
17
revised Inertial forces and centre of mass
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Jan
17
revised Inertial forces and centre of mass
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Jan
15
comment How to calculate the moment of inertia of a 2 point mass system
Are you looking for the MMOI about the rod center, or the center of mass? The former is going to be larger than the latter.
Jan
15
comment How to calculate the moment of inertia of a 2 point mass system
This is the MMOI about the rod center, and not the center of mass. Of course the OP wasn't clear where the MMOI should be measured.
Jan
14
comment Momentum of slowly spinning (viscous) fluid
Yes,$$\dot{v} = \frac{\partial v}{\partial t} \\ v' = \frac{\partial v}{\partial r}$$
Jan
14
comment Momentum of slowly spinning (viscous) fluid
I think the solution might contain $\exp(-\beta t) \sinh(\beta \sqrt{\frac{\rho}{\mu}} r)$ terms
Jan
14
comment Momentum of slowly spinning (viscous) fluid
@VictorPira yes, but I might have made a mistake in the PDE derivation.
Jan
14
comment Momentum of slowly spinning (viscous) fluid
First I'd like to know if there is an analytical solution. If that is not possible, then any numerical results will give me the typical velocity profile and the momentum over time. If it exponential, I'd like to know the coefficient $\beta$ from $\exp(-\beta t)$ terms.
Jan
14
awarded  Promoter
Jan
14
comment Momentum of slowly spinning (viscous) fluid
What I am really interested in is the shape of the momentum curve over time.
Jan
13
answered Deformation of an elastic bar
Jan
13
comment Deformation of an elastic bar
For a bar fixed at one end with gravity the deflection would be $s = A \cdot w \ell^4$ where $w$ is the unit weight of the beam (weight/length).
Jan
13
comment Deformation of an elastic bar
If $F$ is gravitational force then it is applied uniformly along the beam and not at the end.
Jan
12
comment Maximum possible acceleration value on a ball in volleyball game
There is a lot going on when a ball impacts something. Have you seen this: youtube.com/watch?v=aMqM13EUSKw