Wikipedia:Reference desk/Archives/Science/2016 August 18

= August 18 =

Good Calculus-Based Physics Book
Can someone please recommend a good introductory physics textbook that explains the concepts using calculus, rather than algebra? I have one of the standard intro textbooks, and I'm having trouble bridging the gap from the simplified explanations it provides to the more mathematically rigorous ones that I find elsewhere. For example, the Wikipedia page on work defines it in terms of a line integral: I know how to work with those, but the examples from my calculus textbook are too abstract for me to know how to apply them to real-world problems (e.g. they use generic polynomial functions), and the examples from my physics book only use algebra. I want to see some worked examples of actual physics problems that are modeled using calculus and differential equations, with enough explanation of the concepts involved so that I can link the concepts to the model. Thanks!OldTimeNESter (talk) 12:35, 18 August 2016 (UTC)


 * Hate to say this but:
 * Calculus is not distinct from Algebra
 * "F = m a" (where a is a vector) is the basis of Newtonian physics. And is an Algebraic form   And so on.   Newton's development of Calculus - requires use of Algebra. Acceleration is the first derivative of velocity, which is the first derivative of distance (by time).  Collect (talk) 13:55, 18 August 2016 (UTC)
 * Well ok but I think OP wants a text book that includes e.g. integrals of time-varying forces, and goes beyond the simple cases used in many intro books, where the integral reduces to a simple multiplication, and the fact that there is integration behind the scenes is not even mentioned. I think I know the kind of book OP is talking about, it's commonly used for physics electives taught to non-science or non-hard-science majors, and does not have calculus as a prerequisite. SemanticMantis (talk) 15:23, 18 August 2016 (UTC)


 * I found Tipler's Physics for Scientists and Engineers to be great. Its latest edition is available for purchase.  Which book are you presently using, and what issues are you finding?  This feedback might help us find you a better book in a different style.
 * Nimur (talk) 14:00, 18 August 2016 (UTC)


 * If you are looking for introductory book, you might try Serway's Physics for Scientists and Engineers. It is easily understood and widely used college textbook at an introductory level.  I would describe it more as "Physics with some Calculus" rather than "calculus-based physics".  Most topics are introduced with algebra and then the book generally provides examples of how it would be used with calculus.  In that way it is perhaps less intense than some other texts, but maybe that is what you would prefer?  If you do choose Serway, look for one of the used editions.  Used versions will save you a lot of money, and basic physics doesn't change so quickly that you need to read the most recent edition.  Dragons flight (talk) 14:58, 18 August 2016 (UTC)

Do EpiPens actually expire and why?
Apparently the expiration date is six months after purchase, but do they still maintain their effectiveness after that?Timtempleton (talk) 17:03, 18 August 2016 (UTC)


 * If they tell you the expiration date is 6 months, then, you cannot expect that it works as it says on the can after 6 months. You would be using it at your own peril after this time.
 * However, pens that have been properly stored continue to have potency several years past the expiration date. If an emergency arises, it is better to use an outdated pen than to not to use it.--Llaanngg (talk) 17:08, 18 August 2016 (UTC)


 * BTW, notice that the expiration cannot be in reference to your purchase since they don't know when that will happen. They probably are allowed to sell epipens with at least 6 months official expiration date, but I am sure they last longer than that. Llaanngg (talk) 17:38, 18 August 2016 (UTC)


 * Is the expiration date printed on the device (or dose unit) itself, or on the scrip or separate instructions from the pharmacy? I just checked the prescription medications in my house, and almost all have a parmacy-label with a "discard after" date 1 year after the "filled" date. That's both for pills (where the pharmacy dispensed them from a stock that presumably has an exp-date according to its manufacture) and for prepackaged or single-dose-units. It seems coincidental that all different types of drugs would have a 1-year shelflife from exactly whatever date it was dispensed! A few have other dates, so it's getting transcribed from...somewhere...at least sometime. But the single-unit/prepackaged items have their own exp-dates on them, which is not the same as the 1-year-from-fill on the pharmacy-printed label. Fortunately, I could not find any cases where the product's own packaging had an earlier date than the pharmacy printed. DMacks (talk) 17:57, 18 August 2016 (UTC)
 * This is one of those troubling cases where you feel like someone's getting away with something disgraceful, but there's not much you can do about it. Mylan has drastically increased the price of the EpiPen (see here and here, for example).  They have an obvious incentive to keep expiry dates short, in order to increase repeat purchases.
 * But on the other hand, maybe the contents do expire. Obviously we don't want people relying on unreliable pens; people could die.
 * I would love to see some genuine independent testing, under realistic conditions, maybe by someone like Consumer Reports, to see what actually happens to the contents and in what time frame. If such testing has been done, I would love to see a link to it.  But obviously there is no way anyone here can responsibly say that it is OK to delay refilling a prescription.  Even if we're not any too sure we trust Mylan. --Trovatore (talk) 18:26, 18 August 2016 (UTC)
 * By the way, it occurs to me that I was assuming, in the above, that Mylan has something to do with setting the expiry dates. I don't actually know whether that is true.  Can anyone clarify on that point? --Trovatore (talk) 18:30, 18 August 2016 (UTC)


 * You may wish to search and see it their post-expiration effectiveness has been studied in the US Federal Shelf Life Extension Program. -- ToE 18:32, 18 August 2016 (UTC)


 * Outdated EpiPen and EpiPen Jr autoinjectors: past their prime? from J Allergy Clin Immunol. 2000 May. -- ToE 18:46, 18 August 2016 (UTC)
 * Interesting, tantalizing, frustrating link. The abstract says that the observed loss of potency after the expiry date is statistically significant &mdash; let me just point out here that that doesn't necessarily mean clinically significant.  It just means that the observation would be unlikely to happen just by chance.
 * Similarly, it gives a correlation coefficient of 0.63 for the correlation between months past expiry date and reduction in potency. But that, by itself, doesn't tell you anything at all about how much potency is reduced per month.  It just gives a measure of how much of the reduction appears to be systematic, as opposed to statistical fluctuation.
 * So we now know, with reasonable confidence, that potency drops past the expiry date, and keeps dropping. But we're basically none the wiser about whether that actually matters.  --Trovatore (talk) 18:58, 18 August 2016 (UTC)
 * You could read the actual paper?   The key figure  seems to be showing a trend line with about a 40% decline at 90 months post-expiration, but with a wide variations (likely depending on how the material was stored).  One sample lost 30% of activity only 12 months after expiration, another was almost 80% effective after nearly 80 months post-expiration.   Dragons flight (talk) 19:27, 18 August 2016 (UTC)
 * Ah, I assumed you'd have to pay to get the full text. Thanks for finding that. --Trovatore (talk) 19:29, 18 August 2016 (UTC)
 * Indeed, extensive details are in the paper... but not everyone has zero-cost access to that journal. The paper may be purchased from the publisher via the web link.  But even the abstract lists the authors' conclusion, which is to the effect that using an expired EpiPen may still be a better emergency-choice than opting not to administer any epinephrine at all.  This is a really unique product, whose primary users are categorically emergency-users who do not have time to get an expert medical opinion.  Nimur (talk) 19:31, 18 August 2016 (UTC)
 * All old articles (more than 1 year, I think) are free on the journal's website. I didn't login to get it.   Dragons flight (talk) 19:42, 18 August 2016 (UTC)


 * Drugs like these have complex chemical structures which degrade over time. Epinephrine. I have insulin pens with a 2017 use-by date that I got in 2015.  Having lost 70 lbs, I don't use them any more, but they are still in the fridge in case having gotten drunk, I eat an entire blueberry pie.
 * I am not sure why this question is being asked here. The medicine is labelled.  Are we expected as strangers on the internet to know better?  If you want absolution to use it otherwise, seek professional medical advice from whomever prescribed or sold you these potential toxins. μηδείς (talk) 21:50, 18 August 2016 (UTC)
 * Grammar peeve: Should be "whoever", not "whomever".  The case is determined by the fact that it's the subject of the relative clause, not the fact that the clause is the object of the preposition "from".  You can remember it by remembering that it's the clause as a whole, not just the relative pronoun, that's subject or object of the larger sentence, but the relative pronoun by itself is subject or object of the relative clause. --Trovatore (talk) 23:49, 18 August 2016 (UTC)
 * I luvya, Trovatore. But no.  If it is from whom, then it is from whom[ever].  The preposition from is determinant. μηδείς (talk) 01:53, 20 August 2016 (UTC)
 * I posted for a friend and there are some good answers here. Thanks all.Timtempleton (talk) 21:52, 18 August 2016 (UTC)

This was apparently triggered by news of stunning EpiPen price hikes announced August 17, 2016.[].Timtempleton (talk) 22:43, 18 August 2016 (UTC)


 * The patients have adopted a range of different tactics - it is key to note that the "Epipen" is only one way of delivering epinephrine, and others exist even within the tiny universe of what the FDA allows.  Another option described was for patients to go north and buy in Canada; apparently the savings more than pays for the tourism.  They also mentioned Adrenaclick, which is apparently not a "generic epipen" because it works differently, but still is the same chemical for the same purpose.  A big part of the fishing net here is simply deception. Wait, no, somehow the maker of Adrenaclick was induced to stop selling it; also Auvi-Q.   Wnt (talk) 10:53, 19 August 2016 (UTC)


 * The article Epinephrine autoinjector provides a source for the statement Units that have exceeded their expiration date can still be used in an emergency if an unexpired unit is unavailable and the solution is neither discoloured nor contains precipitates. AllBestFaith (talk) 13:16, 19 August 2016 (UTC)


 * Yes, that advice is in line with expired food. Food can go bad before or after the listed expiration date, as that's only an average based on typical usage.  Looking for color changes, texture changes, separation, and smelling it are good methods for checking food, which we should do regardless of whether the expiration date has been reached.  Of course, with food, they don't have as much incentive to shorten expiration dates, as people may just stop buying food with short expiration dates and buy something else.  It's not a life-and-death situation. StuRat (talk) 19:55, 19 August 2016 (UTC)

Is a quadcopter capable of autorotation?
A quadcoptor like this. Imagine it might tumble due to it being top heavy so wouldn't it be better to position the rotors above the fuselage? ScienceApe (talk) 20:40, 18 August 2016 (UTC)
 * To perform autorotation efficiently (and to provide for a more safe touchdown speed), the helicopter must have the ability to control blade pitch. One of the common reasons engineers go for a quad-copter (instead of a conventional helicopter) is that they can build without variable pitch rotors; the vehicle control depends on providing differential power to each rotor, rather than using cyclic and collective.  This applies whether the vehicle is very small or very large.
 * The emergency procedure for any specific design would need to be designed and published by the vehicle manufacturer.
 * The Helicopter Flying Handbook, Emergency Procedures chapter, describes the basic theory of autorotation, and explains the various applications of the technique for a "generic" helicopter.
 * Nimur (talk) 20:58, 18 August 2016 (UTC)
 * The above is mostly correct however the fact it has collective pitch is NOT what differentiates a "conventional" helicopter from a quad copter. There ARE now so called "3D" quad copters that also have collective pitch. They would presumably be capable of a auto rotation, however doing an auto rotation also relies on momentum of the blades, heads and engines, and since those are usually quite small on a quad copter so not sure whether it would actually work, might be one of those "depends" situations. My feeling is that it might not be impossible, but probably harder than with a "conventional" helicopter of the same mass. Though come to think of it, in theory I can't really see why 4 smaller blades that have the same lift as 1 big blade would be worse at autorotation. Vespine (talk) 23:36, 18 August 2016 (UTC)
 * Have a look at autorotation and read the chapter of the Helicopter Flying Handbook I linked. Aerodynamics is not intuitive: for a small-radius rotor, a greater percentage of the disc is in the stall regime during autorotation; consequently, small rotors yield faster rotor RPM without actually slowing the rate of descent.
 * Large rotors also have large blade rotational inertia. This is where the potential energy is stored, and that (plus your altitude, which is a rapidly decreasing resource) is your only reservoir of energy during a power-plant failure.  You will want that reservoir to be as large as possible, especially when you are a foot or two above the ground.
 * "At approximately 1 foot AGL, apply upward collective pitch control, as necessary, to slow the descent and cushion the landing without arresting the rate of descent above the surface. Usually, the full amount of collective pitch is required just as the landing gear touches the surface."
 * Nimur (talk) 23:43, 18 August 2016 (UTC)