1

Physics, Astronomy & Cosmology / Re: How "fast" does force "travel"

« on: 21/06/2019 10:27:07 »

You can hear a train coming down the line (don't try this at home) because the forces are propagating along the steel in the track

I'm glad you warned me not to try this at home.

2

Physics, Astronomy & Cosmology / What is the difference between astronomy and cosmology?

« on: 20/01/2019 12:18:57 »

Hi,
What is the difference between astronomy and cosmology?

3

General Science / Re: Spit vs swallow: why do foods taste nicest only if we swallow them?

« on: 20/01/2019 12:05:17 »

Hi,
The subject asks if taste is better on swallowing vs spitting.  I thought if this is true then why do wine tasters not swallow?  Is it only because of the alcohol?  Besides, I'd think they can't help swallowing a small amount.
However, the question asked is regarding satisfaction rather than the quality of taste.  Also, is the question about the pleasure of swallowing or is it the satisfaction wrt satiation? 

4

Question of the Week / Re: QotW - 10.03.28 - Is a human bite worse than a dog bite?

« on: 13/01/2019 09:14:22 »

One circumstance deserves mention.  Human 'bites' are not uncommon as a result of one person punching another in the mouth.  The injury thus obtained frequently involves penetration into the hitters metacarpo-phalangeal joints, sometimes accompanied by fractures.  Any contaminated injury involving a joint, whether it be canine, human or other, is more serious.  Infection here is harder for the immune system to access and complications are disabling.  This type of injury is overwhelmingly associated with human teeth rather than dog bites and largely is responsible for the human bites' reputation.

5

Question of the Week / Re: QotW - 18.10.28 - When did we become modern day humans?

« on: 12/01/2019 16:09:13 »

Native Americans lacked genetic defenses against European diseases like Measles and Syphilis

The invaders from Europe didn't only bring inadvertent diseases;  they actually impregnated blankets for barter with smallpox.  These were ''modern humans'' and quite comfortable with death sentences.

6

Plant Sciences, Zoology & Evolution / Re: Do ants get lost?

« on: 12/01/2019 15:45:47 »

Thanks Evan and Chris.  Lots of fascinating ant info.  I was thinking along the lines of a lone ant - essentially, taking an ant from its 'comfort zone' among all the familiar chemical signals of fellow ants and their pathways, and transplanting it elsewhere where none of the chemical signals are recognized.   It is sobering to realize that, as you say - ''Unrelated ants trying to get into an ant colony will be quickly recognised and killed.''  I didn't know I was sentencing them to death.

7

Physics, Astronomy & Cosmology / Re: Is a mains-powered light bulb flashing on and off 100 times per second?

« on: 09/01/2019 13:51:19 »

My apologies.  I had intended to phrase my post as a question.  Thanks for the clarifications.

8

Physics, Astronomy & Cosmology / Re: Is a mains-powered light bulb flashing on and off 100 times per second?

« on: 09/01/2019 10:47:51 »

The light emitted by an incandescent light bulb is directly proportional to the filament temperature.  In order to flicker, there would have to be a measurable drop in temperature at the instant of current reversal.  This drop would be equal to the amount of energy lost as light during that instant not replenished by the interaction of the current  and the filament resistance.  An infinitesimal amount I'm sure.

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Plant Sciences, Zoology & Evolution / Do ants get lost?

« on: 09/01/2019 09:38:53 »

What happens to an ant that I blow off my 3rd floor balcony into the garden?  Does it simply join another colony?

10

General Science / Re: Do we pee more than we drink?

« on: 21/11/2018 12:41:04 »

The short answer is – no.  If one were to pee more than one ingested then the result would be dehydration, a condition that if sustained leads to death.
Water intake normally, on average, is about 2000ml/day from drinking and food.  A further 350-400ml is produced metabolically.
The body has an obligatory solute load (minerals and waste products) of +/- 600mosml to excrete per day.  This is effectively all excreted via the kidneys.  Normal kidneys can concentrate urine to a max of 1200mosml/litre.  So an obligatory urine loss per day is 500ml. [If one were to take in abnormal amounts of solutes – eg drinking sea water – the obligatory urine loss would be greater than 500ml/d, resulting in more rapid dehydration]
Fluid is also lost per day as insensible loss of 800ml (mostly via the lungs) and 200ml in the faeces i.e. more than metabolic production.  In other words at least 1500ml/d of water is needed to just be in balance. 
Clearly a normal adult has to take in far more water than is lost as urine.

11

Physics, Astronomy & Cosmology / Re: Why do plastic fridge magnets not repel each other?

« on: 09/11/2018 14:29:32 »

Colin2B - Great, that explains it.  Also answers why only small surfaces worked.

[They are distributed with adverts printed on one side.]

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Physics, Astronomy & Cosmology / Re: Why do plastic fridge magnets not repel each other?

« on: 09/11/2018 14:18:19 »

As a newbie, I can't see how to response to answers.
Reply to yor_on:
Thanks.  Using a compass, as suggested, cleared up a lot; polarity is indeed present on edges and surfaces.
Because the fields are so weak,  the trick is to float one on water to to reduce friction and exclude gravity and approach with the other.  The other thing is to use only 1-2mm overlap.  Now I can feel weak repelling as loss of friction.  Attraction is far stronger.   

13

Physics, Astronomy & Cosmology / Why do plastic fridge magnets not repel each other?

« on: 09/11/2018 12:05:41 »

By plastic magnet, I am not talking about a magnet glued onto a plastic item.  I'm talking about the magnets made from plastic of sorts, flexible, roughly the same shape, size and thickness as a typical 'business card' and, just as thin.  Ads are usually printed on one surface; see photo below.

magnets3.jpg (54.67 kB . 656x492 - viewed 10406 times)

No matter how I orientated the two I could not sense any repelling and they always stuck together.
Note that the flat magnets that I used were not printed on either side.
Surely they must have polarity?