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visits member for 1 year, 7 months
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Apr
15
comment What are the eigenvalues of the Lorentz matrix?
I recommend you try to answer and interpret the third one for yourself!
Apr
13
comment Why does pitch in a helicopter take effect 90 degrees later?
Could it simply be that you want the helicopter blade to "bite" for the full 180 degrees centered around the perpendicular position? (by "perpendicular position" I mean where the blade is perpendicular to the aircraft)
Apr
13
comment Relation between shm and circular motion
Note also that $x=a \sin(t)$ $y=a \sin(t\pm \pi/2)$ satisfies $x^2+y^2=a^2$, hence the "differing in phase by $\pi/2$".
Apr
3
comment Some subtleties in direction of drag force
@CAF you did it again! The equation is already for $v$ in the upwards direction. You don't need to do that, you can just multiply the equation $F=-mg-\mu v$ by $\hat{x}$ and be done with it. The corresponding vector equation is $F \hat{x}=-mg\hat{x}-\mu v\hat{x}$ or $\mathbf{F}=-mg\hat{x}-\mu \mathbf{v}$.
Apr
3
comment Pendulum (highschool)
In case you are not aware, that still is an approximation to the exact period! For the full formula, see: en.wikipedia.org/wiki/…
Apr
2
comment Why is water clear?
See also: Why is Glass Transparent? youtube.com/watch?v=Omr0JNyDBI0
Apr
2
comment How is the image in a mirror created? Are there infinitely many light rays?
By "God" do you happen to happen to mean "image sensors" or "retina"?
Mar
31
comment Why does the gas cloud of an underwater gunshot pulse?
@Hoytman, so my point really is just that to understand the dynamics of the system, you should realize that the compression of the air is very important, while the compression of the water is not.
Mar
31
comment Why does the gas cloud of an underwater gunshot pulse?
@Hoytman, So, the water stores potential energy (as it is pushed away, working against the pressure of the rest of the water) and kinetic energy (at times when it has velocity), but my point phrased another way is: If you took a container of water at the bottom of the sea, lifted it up to the surface, and poked a hole in it, the water would release a tiny bit of energy and that would be the end of it. If you took a container of air at sea level and lifted it up to space, then poked a hole in it, you would get a lot of energy from it.
Mar
30
comment Why does the gas cloud of an underwater gunshot pulse?
@leftaroundabout What can I say - I think that gross oversimplification is fine for non-technical questions, and I think that discussion of oscillatory phenomena in general adds to an understanding of this. Overshoot/undershoot from equilibrium, even though there may be no equilibrium, among other problems.
Mar
30
comment Why does the gas cloud of an underwater gunshot pulse?
@leftaroundabout Okay, I'm not doing pulsing bubbles justice at all, but this page en.wikipedia.org/wiki/Liquid_bubble#Pulsation seems to imply that the amplitude is independent of initial displacement from equilibrium [in that specific case] (I say nothing about the bubble radius). I'm not familiar with much about nonlinear ODEs but this seems fine to me. (if I was familiar I'd try to do things more formally to see whether I'm right or wrong, but at the moment I'd probably spend way too long on it before I got anywhere)
Mar
20
comment A question about biceps and rotational equilibrium
It is not totally true that there is $0$ force when the angle is $180^{\circ}$, because the point of application of force from the bicep can be offset a bit and may not point directly through the pivot point of the elbow.
Mar
7
comment How can I destroy earth with physics?
That's a boring question; you can't destroy the earth without using physics!
Mar
4
comment Work producing current = energy stored in the magnetic field?
Add a "for an idealized inductor with no resistance" somewhere. Not everyone has circuits on the mind!
Feb
22
comment Numerical solution of two coupled second order differential equations of motion
This is more like a first order equation - treat your variables as $\dot{x}$ and $\dot{y}$. (it IS a first order equation in $\dot{x}$ and $\dot{y}$.)
Feb
20
comment How to simulate a full-suspension bike?
A few questions for background: Are you asking "what model is best" or "how do I apply physical laws to a model"? Are you familiar at all with the Lagrangian formulation of Newtonian mechanics? And how would you propose one model the rider? Anyways, the first step is parameterizing the bike - what are all the important variables and spatial relationships between them. eg, finding the position of the rear wheel given a front wheel position and hydraulic compression amount. There is little physics involved in that step - mostly taste and geometry.
Feb
19
comment Why light can't go faster then 300 000 km/s? What prevents it?
There is also physics.stackexchange.com/q/92079/12029 which isn't quite a duplicate but is very close.
Feb
3
comment What is difference between Acceleration due to gravity and Gravitational field intensity near the Earth Surface?
-1. Please clarify your definitions of "gravitational intensity" and "gravitational acceleration". With the definitions I'd go with (g-field as the sum of all fields produced by all point masses) the statement "it does not imply that the gravitational acceleration of any [point] mass at that point is equal to E" is false. (the field produced by the point mass itself is ignored)
Feb
3
comment Collision of multiple fluid flows at a point
youtube.com/watch?v=kvRg9NuO9Oc it seems like the key phrase to google for is "impinging fluid jet"
Jan
30
comment Pseudo Force Other Than Centrifugal Force In A Rotating Frame
If you apply the transformation in full generality you get the centrifugal force and the coriolis force, as derived at: physics.stackexchange.com/q/383