Wikipedia:Reference desk/Archives/Science/2016 December 6

= December 6 =

School systems in America, England and Holland


Please do not solicit from this desk. It is inappropriate. Seek other means to get your surveys completed. Tobyc75 (talk) 18:09, 6 December 2016 (UTC)

Which school system is better: the Dutch, American or British one?


Please do not solicit from this desk. It is inappropriate. Seek other means to get your surveys completed. -- Jayron 32 17:07, 6 December 2016 (UTC)

The Singaporean one:

"Prof Sing Kong Lee, vice-president of Nanyang Technological University, which houses Singapore's National Institute of Education, said a key factor had been the standard of teaching. "Singapore invested heavily in a quality teaching force - to raise up the prestige and status of teaching and to attract the best graduates," said Prof Lee. The country recruits its teachers from the top 5% of graduates in a system that is highly centralized." Count Iblis (talk) 22:36, 6 December 2016 (UTC)
 * So, in essence, the answer to the OP's question is "No"? ←Baseball Bugs What's up, Doc? carrots→ 22:41, 6 December 2016 (UTC)
 * Not the OP's own system, apparently - or he would know that it is always the better of two, but the best of three or more. Wymspen (talk) 23:02, 6 December 2016 (UTC)
 * Unless each one is better than the other two. ←Baseball Bugs What's up, Doc? carrots→ 00:49, 7 December 2016 (UTC)
 * There's no "American" school system anyway. Shock Brigade Harvester Boris (talk) 01:21, 7 December 2016 (UTC)
 * Yes, American schools are operated at the state level, but there are also federal standards. ←Baseball Bugs What's up, Doc? carrots→ 10:02, 7 December 2016 (UTC)


 * No, there aren't. There are national or sort-of-national standards which have been developed by the states collectively without the participation of the Federal Government, such as the Common Core State Standards Initiative, but the Federal Government does not mandate any standards on their own, as noted here at www.ed.gov, the U.S. Department of Education encourages states to develop their own standards, but has no say in what those standards are.  To quote that webpage "Federal law requires that all states receiving Title I funds have high-quality standards. Federal law does not mandate a specific set of standards."  (bold mine).  -- Jayron 32 00:33, 8 December 2016 (UTC)
 * Yes, federal standards exist; see Title IX, for example, which despite being part of the Higher Education Amendments of 1972, applies to non-higher educational institutions as well. The Family Educational Rights and Privacy Act also imposes standards on schools at all levels.  These standards apply only to schools accepting federal funding, but given the appearance of largesse from Washington and the consequent pressure on legislators to accept it, virtually all schools accept federal funding.  Nyttend (talk) 05:41, 9 December 2016 (UTC)

When photons hit solar sails
Does the photons lose momentum? Could they hit infinitely many solar sails and move these without losing momentum? Doesn't this sound like energy for free? — Preceding unsigned comment added by Quotawk (talk • contribs) 19:04, 6 December 2016 (UTC)


 * One photon between two mirrors could, in principle, continue bouncing off each and pushing it in the opposite direction indefinitely. The combined momentum remains conserved.  But where does the energy come from?  Well, supposing a perfect mirror, the photon bounces off each object exactly the same way as it arrived... from the perspective of the mirror.  That means that if the mirrors are moving away from each other, the photon, from the average perspective that sees them diverging, is coming back with a little less momentum each time.  In other words, it is redder due to a Doppler shift.  (The photon would actually be able to gain energy for a while if the mirrors were heading toward each other instead, but then again, it would be nothing unusual for them to hit each other and bounce - and whatever energy it gained would be lost due to the decreasing energy of the collision at the time they did hit each other, because it had slowed them a little first) Wnt (talk) 19:14, 6 December 2016 (UTC)


 * You can read about this at Solar sail and radiation pressure. As explained at that second article, the photons do lose momentum; basically a photon's momentum is related to its frequency (p = h/c * ν), so when momentum is transferred to the sail, the light gets redder.  -- Jayron 32 19:17, 6 December 2016 (UTC)


 * Yes. Note that the momentum of a photon is not constant in this regard, but depends on its energy, which is to say its frequency, which in turn (like momentum measurements of anything else) depends on what frame of reference it is viewed in.  So in every frame it moves with the same speed but in frames where it is redder it has less momentum. Wnt (talk) 19:19, 6 December 2016 (UTC)


 * Right, whether we assume the reddening of the light is because, from the point of view of the accelerating sail, the light has become Doppler shifted to the red, or because of the DeBroglie relation, the photon loses momentum and this decreases in frequency (thus becoming redder) is the same concept viewed from two different perspectives. Either way, the laws of physics are happily obeyed.  -- Jayron 32 19:23, 6 December 2016 (UTC)


 * OK, thanks for the answers.