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Jan
16
answered To calculate pressure at point in a vertical water pipe of given diameter
Jan
16
comment Planetary model of atom still valid?
The details of chemical bonds is inexplicable - but a lot of inorganic chemistry is fairly well predicted by simply gaining or losing valence electrons. As models go it's pretty good value for money!
Jan
16
comment Planetary model of atom still valid?
All models are invalid - some models are useful. That's basically the definition of physics.
Jan
15
answered Kinetic energy absorbing in order to avoid damages?
Jan
14
revised Why does $E=mc^2$ give results in Joules?
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Jan
14
comment Will a photon emitted from something moving quickly have a shorter wavelength?
I don't think it's useful to consider this as energy from the emitter's speed. Photons don't have mass and so don't gain kinetic energy from the source's movement
Jan
12
answered Does interchangeable wavelength LED exist in NIR?
Jan
11
answered Light pollution calculation using camera
Jan
11
answered How fast will the projectile go the second time?
Jan
11
comment How to read a lens spot diagram?
It looks to me like those are the on-axis spots at different positions OF the surface - ie at different focus?
Jan
8
revised If microwave ovens and WiFi both operate on the same frequency, why doesn't WiFi cook things?
added 379 characters in body
Jan
8
comment Why is it concluded that the cosmos is expanding when in fact the observations are for events further back in time?
I think DDD's point was that if we see more distant objects moving faster but more distant objects are also older then that is saying that the universe is slowing - older=faster, younger=slower! In fact the expansion of the universe doesn't quite work likethat
Jan
8
answered If microwave ovens and WiFi both operate on the same frequency, why doesn't WiFi cook things?
Jan
6
comment How far does physics influence russian roulette?
See qi.com/talk/viewtopic.php?start=15&t=3032
Jan
6
answered How does water carve rock?
Jan
5
comment What fundamental principles or theories are required by modern physics?
@Ron. Yes. You can't say faster than light is impossible because it breaks Relativity. Theories, however elegant, can't override results. Although if you had a measurement of FTL you would need a good explanation of why it didn't violate a lot of basic principles that seem to work!
Jan
5
comment What fundamental principles or theories are required by modern physics?
@Ron, my objection was that there had to be a meta-criterion. Protons and electrons everywhere have the same (but opposite) charge. We don't know the reason for this - yet we can describe it without knowing why. There could be a circumstance in which electrons/protons had differing charges but it would have to be very bizarre circumstances since we haven't seen any effects of it in any other observation.
Jan
5
revised What fundamental principles or theories are required by modern physics?
added 606 characters in body
Jan
5
comment What fundamental principles or theories are required by modern physics?
@Ron - no there isn't - theoretical physics might like to think there is. In reality there is a theory which explains everything, then a tiny little experimental result doesn't fit and you need a whole new theory (eg relativity). If it was discovered that eg. you could send a signal faster than light by some QM effect - but over a distance <0.1nm and only below a temperature of 1mK that would invalidate relativity but have no affect on the day-day use of relativity in physics. In exactly the same way that GR had no effect on calculating the flight of cannon-balls.
Jan
5
comment What fundamental principles or theories are required by modern physics?
@Ron - then the results can't be true! The point is that any 'impossible' result must still allow all current experimental results.