Wikipedia:Reference desk/Archives/Science/2017 November 9

= November 9 =

Forensic analysis
Are there forensic techniques which can determine, by analyzing microscopic scratches, markings, etc., whether a large rock had made an impact against a painted metal surface, in the absence of damage visible to the naked eye (provided, of course, that the surface had not been repainted afterward)? In other words, suppose someone threw a large rock against a car, but it bounced off without causing any visible damage -- is it possible to prove that this happened? 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 09:25, 9 November 2017 (UTC)
 * I doubt much can be told if nothing is straightforwardly visible. The paint on modern cars is a flexible cross linked polymer, not an enamel, so there won't be small cracks. It is amazing what forensics can do but I can't see how even if they found something they could tell when it happened and cars are always being hit by small stones and this as they are going along. Dmcq (talk) 10:35, 9 November 2017 (UTC)


 * Without answering the specific question, which is probably outside of the realm of this desk, I can direct the reader to concepts like trace evidence analysis which is a HUGE sub-discipline within forensic science. Our article is short, but the answer to your question is part of trace evidence analysis, and if you want to know what that field can do, that is a phrase to punch into google to research more.  -- Jayron 32 12:18, 9 November 2017 (UTC)
 * Thanks for the bad news. 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 02:58, 10 November 2017 (UTC)


 * I don't see why this is a slam dunk. My parents' neighbours' son got drunk one night and hit 11 parked cars (including my father's) over some distance before returning home.  The insurer was able to tell that the damage to my dad's car was done by the neighbours' car, by analyzing microscopic bits of paint on each vehicle.  They refused to pay, and the driver had to be charged with "theft" of the vehicle by his parents, or they would have been liable for the damage, so he ended up being arrested based on that not-visible to the eye forensic evidence.  This was in the 80's, so I suspect the forensic science is better now. μηδείς (talk) 22:57, 10 November 2017 (UTC)


 * As a car owner, I'm struggling to think how a large rock could be thrown against a car's painted exterior and not cause any damage visible to the naked eye. If there were no such damage, how would one know that the event had happened at all, unless it had been witnessed? I presume also that to prove such an impact, one would have to identify traces on both the car and the rock (which ought to be possible if any damage did occur and the rock is available for analysis). {The poster formerly known as 87.81.230.195} 90.200.138.27 (talk) 00:32, 11 November 2017 (UTC)
 * The relevant forensic idea IP and Medeis are discussing is Locard's exchange principle. DMacks (talk) 21:46, 11 November 2017 (UTC)
 * Sounds like the story in The Third Policeman that cyclists are part bicycle and bicycles are part human. When cyclists get to be more than half bicycle they spend most of their time leaning on walls or propped up by one foot on a kerb. ;-) Dmcq (talk) 22:13, 11 November 2017 (UTC)

iPTF14hls, cause of survival of explosions?
Could iPTF14hls contain a huge amount of weakly interacting dark matter? Because the dark matter is weakly interacting, it wouldn't get expelled by explosions, and its strong gravity could suck more fusionable matter in to fuel a later explosion. Thanks144.35.114.29 (talk) 19:47, 9 November 2017 (UTC)


 * Stellar objects do not contain dark matter as there is no plausible mechanism that can explain how dark matter is captured into a stellar object in the first place - it is weakly interacting after all. As to iPTF14hls it is likely not a supernova at all. It just looks similar. Ruslik_ Zero 20:13, 9 November 2017 (UTC)
 * First of all, I'm sure you meant to say don't contain rather than do contain. Second, I didn't claim it was a supernova, and whether it is or isn't a supernova might not be relevant to my question. Third, weakly interacting dark matter still interacts via gravitation, and a dense plume of dark matter could plausibly been the birth site of the star. There are other plausible scenarios.
 * ??144.35.45.45 (talk) 00:25, 10 November 2017 (UTC)
 * Yes, I meant "don't'. Ruslik_ Zero 19:28, 10 November 2017 (UTC)

Site engineers
If site engineers are entry level roles, why are there trainee and assistant site engineer jobs and why do nearly all site engineer jobs require previous experience of it? 94.10.251.123 (talk) 23:56, 9 November 2017 (UTC)


 * The problem seems to be with the words following "if". Who claims this?  Our article Construction engineering mentions some entry-level jobs suitable for a graduate in engineering.  Some of these will be described as "trainee" or "assistant" depending on the complexity of the operation. Experience is highly valued in many professions.  D b f i r s   07:43, 10 November 2017 (UTC)
 * I thought site engineer is an entry level role is it not? 94.10.251.123 (talk) 08:35, 10 November 2017 (UTC)
 * Where did you see that? ←Baseball Bugs What's up, Doc? carrots→ 08:51, 10 November 2017 (UTC)
 * Terminology in this field is not standardized, and much depends on the scale of the project. Some companies have this as entry level job, others make it an intermediate level of management and administration. Most project engineers have construction experience and have a role equivalent to an assistant project superintendent, at least so they can provide supervisory coverage when the superintendent or assistant is absent.  Acroterion   (talk)   17:53, 10 November 2017 (UTC)