Mark Rovetta

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I participate on this site because I really enjoy physics and because I would like to learn more about what makes an online community work well. Questions often interest me more than answers – although I think the best answers are grounded in observation and experiment. I’m optimistic that there are still many surprising discoveries yet to be made in the physical sciences. I believe physicists should be good citizens. I believe my children will know things about the natural world I can’t even imagine – and will learn them in ways quite different than how I was educated.

	1,117 reputation	bio	website		visits	member for	7 months
13 badges		location	Seattle, WA		seen	37 mins ago

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38m	comment	Time of Measurement Vs Number of Measurements Good answer. I'd also say this can become a practical question if the experiment is powered by a battery. For example, what if you were counting earthquake on Mars - is it better to count for one long continuous time interval, or make repeated shorter duration measurements over a longer period of time.
May 9	comment	Explanation for breaking up of a stream of water into droplets This sounds like classic Plateau-Raleigh instability of fluid jet. You should be able to find several sources for this analysis on the web under that name.
May 6	comment	What is the difference between lattice vectors and basis vectors? Yes thanks, you are correct. I think the explanation in the link above is how crystallographers use these terms.
May 6	comment	What would be the basis vectors for this 2D crystal structure? Yes I think this is the best-correct answer.
May 1	comment	I can't figure out crystal planes with negative intercepts You may be aware of this already but I believe these are Miller Indices - are you familiar with those?
May 1	comment	Where do high-energy neutrinos come from? Thanks, that paper really addresses my question. I'd also mention the title too: "Best-Bet Astrophysical Neutrino Sources"
Apr 29	comment	What determines the angle of the cushion on a pool table? This analysis claims the 'sweet spot' of a pool ball is (7/5)r . I would have guessed that height was the reason for table design, rather than a particular angle.
Apr 29	comment	Michelson–Morley @ Home I honestly don't recall how far we took the lab in class or what the precision was (I did this as a student a long time ago!) but it was an actual laboratory using lasers performed as part of a unit about the 'classic' MM experiment to measure the aether.
Apr 26	comment	What is the most optimal earth's axial tilt in terms of variation of seasons? Uranus has an axial tilt of 97.77 degrees. I can imagine an exoplanet being discovered with a similar tilt. It would fall to physics to discover the tilt and then try to predict what impact this would have on climate. If the planet was otherwise earth-like there would be great interest to understand the impact of axis tilt on habitability.
Apr 23	comment	How much information about the scale of a waterfall can be obtained from its sound? Thanks for sharing your experience. I find it always interesting to hear from someone that is actually performing experiments!
Mar 26	comment	What is a strain gauge and how do I use one? +1 for fine description of most common type of strain gauge. Comment just to point out that many other unconventional designs are possible as well.
Mar 12	comment	a few equations describing the universe "Just Six Numbers: The Deep Forces That Shape The Universe" by Martin Rees
Mar 8	comment	Magnetic field line length Yes, as you noted, there is a component of the geomagnetic observed that is not described by the single dipole model (as much as 20% in some places.) This is due to the interaction of solar particles and ionosphere, rock-magnetism of the earth's crust, and the non-dipole components of the field generated in the outer core.
Mar 7	comment	Glass pipe cutting In that case, the cost of a diamond wafer saw may not seem that much.
Mar 3	comment	How to measure a solid-solid surface energy? This was just a thought. At small grain sizes, the rate of grain-growth and diffusion creep, might be determined by the creation or annihilation of "vacancies and interstitials" near moving grain-boundary. Thermally activated rate (Arrhenius law) and rate measurements of the process might estimate the effective activation energy. A model of the process it might estimate an average formation energy for grain boundary. At best an estimate of an average, grain-boundary energy for a multi-phase polycrystal. See Diffusion creep
Mar 2	comment	What made us think that Earth moves around the Sun? Galileo is my favorite physicist. Just is.
Mar 2	comment	What if the earth's core goes cold? It is not necessary for the Earth's core to freeze for the geomagnetic field to collapse. The geomagnetic field is a chaotic phenomena and has reversed polarity many times in the Earth's history. The question is why are we so fortunate to have a persistent geomagnetic field at all? I believe Mars has a molten core, but a much weaker magnetic field than Earth. Mars lacks a natural satellite as large as Earth's Moon. What role has our Moon played in creating a persistent geomagnetic field? There's a worthy geophysical question!
Feb 28	comment	How to measure a solid-solid surface energy? Think about high-temperature creep experiments using very fine-grained polycrystalline samples to measure the thermal activation energy of pure diffusion creep. You might be able to estimate the average inter-granular surface energy using a diffusion-creep law.
Feb 22	comment	Rubber band stretched produces heat and when released absorbs heat.. Why? A good answer but my rubber bands only seem to get warmer when they are stretched and released. How can I do this to make it cool a lot?
Feb 18	comment	Is the altitude of the surface of the ice at the south pole determined by barometric pressure? David Tressel Griggs was an American that did early experiments of high temperature creep of rocks and minerals. Yes, glacial ice flows on geological timescales. The creep mechanisms are the same as other crystalline solids. Many are thermally activated, and proceed at exponentially faster rates as temperature increases. Temperatures near melting temperature are the highest temperatures and remain a solid. You cannot understand tectonic processes without understanding that on geologic time scales rocks and minerals flow.