143,725 reputation
13244403
bio website ratsauce.co.uk
location Chester, United Kingdom
age 54
visits member for 4 years, 6 months
seen 6 hours ago

Semi retired old time computer nerd who started programming on a Commodore Pet.

Since I'm also active in the Physics forum I should add that I started as a theoretical chemist, moved into solid state photochemistry and finally worked in industry as a colloid scientist. I only became a full time computer nerd in 1997.


Jan
25
comment One dimensional motion problem
Galilean relativity
Jan
25
comment One dimensional motion problem
Divide the initial separation by the relative speed
Jan
25
comment Is the oscillation of all particles for stationary wave equal?
Assuming you mean a standing wave, then you are quite correct. The particles at a node are stationary.
Jan
25
comment Does the payload of an Alcubierre drive have to be on board during the preparation phase?
Why do you say the destination doesn't have to be in the forward light cone? The whole point of FTL drives like the Alcubierre drive is that the destination can be spacelike separated.
Jan
25
comment What evidence is there for quantum leaps?
You might also be interested to read physics.stackexchange.com/questions/142373/…, physics.stackexchange.com/questions/130116/… and physics.stackexchange.com/questions/95211/… as these cover related issues.
Jan
24
comment Clearing up confusion about orbital mechanics
The radial accln is $v^2/r$. The gravitational acceln is $GM/r^2$. If they were equal the net force would be zero and the object would stay at the same distance from the Earth i.e. a circular orbit. At the perigee $v^2/r > GM/r^2$ so the net force is outwards and the body moves away from the Earth. At the apogee $v^2/r < GM/r^2$ so the net force is inwards and the body moves towards the Earth. That's why $r$ changes in an elliptical orbit. The relationship between $v$ and $r$ is given by the vis-viva equation.
Jan
24
comment Special relativity - twin paradox explored
The situation is not symmetric. In frame (1) rocket man 2 is moving at 0.5c and rocket man 3 is moving at -0.5. In frame (2) the Earth is moving at -0.5c and rocket man 3 is moving at -0.8c. In frame (3) the Earth is moving at 0.5c and rocket man 2 is moving at 0.8c. Since there is no symmetry there is no paradox.
Jan
24
comment Interaction between charged particles through static electric fields
Well quantum electrodynamics describes the interaction as the exchange of virtual photons. Does that count?
Jan
24
comment Clearing up confusion about orbital mechanics
Yes, that's true. But at the apogee the centripetal acceleration is not equal to the gravitational acceleration $GM/r^2$. The equation $v = \sqrt{GM/r}$ is true only when the centripetal and gravitational accelerations are equal.
Jan
23
comment paramagnets with high magnetic susceptibility
Have you compared the magnetic susceptibility of ferromagnets and paramagnets?
Jan
23
comment Clearing up confusion about orbital mechanics
The equation $v = \sqrt{GM/r}$ is only true for a circular orbit because it is derived assuming the gravitational acceleration is equal to the acceleration towards the centre. It is not true at the perigee of an elliptical orbit.
Jan
23
comment Why does a magnetic field go anticlockwise of the direction of current?
The magnetic field doesn't go anywhere. We conventionally draw field lines going from North to South, but that's just a convention. So the choice of clockwise vs anticlockwise is just a convention. If we decided field lines went from South to North then the field lines would go anticlockwise not clockwise.
Jan
23
comment Acceleration of stationary observers in their own reference frame?
@Mr.T: I've edited my answer to reply to your comment.
Jan
23
comment Why hasn't an exact solution to the Navier-Stokes equations been found?
Nathaniel beat me to it! All I would add is that Terence Tao has an excellent (as usual :-) article on the problem on his blog. The article should be accessible to most physicists if perhaps not the general public.
Jan
23
comment Can we have a black hole without a singularity?
@SiegeX: that's a bit involved to answer in a comment. You might want to post it as a question.
Jan
23
comment Why can't dark matter be baryonic?
@Michael: all quark based matter is baryonic. In this context the term baryonic means all matter composed of the fundamental particles in the standard model.
Jan
22
comment Hubble time, the age of the Universe and expansion rate
You can find a detailed calculation of the Hubble time in this answer of mine. The figures I get broadly agree with Camiel's.
Jan
22
comment What is an “equation of motion” as used in context of geodesic equation?
You might be interested to read Curvature gravity and a falling apple?
Jan
22
comment Is there a magnetic line that is a Eucliden straight line?
To expand on this, a magnetic field line can only begin or end on a magnetic monopole. Since magnetic monopoles don't exist (probably) all magnetic field lines must have no beginning or end i.e. they must be loops. And obviously a loop cannot be straight over its whole length, or it wouldn't be a loop.
Jan
22
comment The velocity of the flowing coming out of the balloons?
@DavidMichaele: $Q = vA$ where $v$ is the (average) velocity in the tube and $A$ is the tube area.