141

Cells, Microbes & Viruses / Re: Why does the skin on my fingers wrinkle when I stay in the water too long?

« on: 02/11/2016 22:57:43 »

Its an evolutionary adaptation.  The wrinkling increases your ability to grip objects under wet conditions, thus the body is conditioned to cause those wrinkles under the proper stimulus.  One of the clues that led to this conclusion was that people with nerve damage did not get this wrinkling when their hands were soaked in water.

142

Physics, Astronomy & Cosmology / Re: If one were to in some miraculous way, able to pee standing on the surface of the Moon, what kin

« on: 01/11/2016 18:49:09 »

It works out to ~6 times further and higher.  As far as the shape goes- At the speed you are likely able to pee at, you will be hard pressed to notice a difference between the shape of the curve on the moon vs on the Earth.  There will be a very slight difference however.  Here's why:

Even on the Earth and neglecting air resistance, the arc will not follow a parabola, instead it follows a section of an ellipse. This is because the direction of the force of gravity is not parallel at all points of its path but rather point towards the center of the Earth, in addition, gravity is not constant with height.  A constant and parallel force of gravity along all points of the path is what is required to get a parabolic path. (in most cases, the real deviation from this ideal case is so small, we can't measure the difference.)

The speed and direction upon launch determines the eccentricity of the ellipse.  On the Moon, where the escape velocity is lower, the same launch speed and direction will produce a path that will be slightly less eccentric (closer to that of a circle) than it would on the Earth,  And thus the arc shape will be slightly different.

To put it another way, imagine you could throw an object a 1.68 km/sec parallel to the ground while standing on the Moon.  This is the circular orbital velocity at the surface.  Assuming no obstacles in its way it would follow a circular path around the Moon maintaining a constant distance above the Moon's surface.

If you threw the same object at the same speed on the surface of the Earth where the circular orbital velocity is much higher, the object's path would follow an ellipse which would intersect the Earth's surface some distance from you.   It is obvious that in the two cases, the object follows a differently shaped trajectory.

P.S.  I should mention that the 6 times further answer I gave above assumes that you are going for maximum distance.  If the initial trajectory was parallel to the ground, then the Moon distance would only be 2.5 times further than the Earth distance.

143

Question of the Week / Re: QotW - 16.10.18 - What would happen if I moved to Jupiter for 50 years?

« on: 30/10/2016 20:11:29 »

A couple of points I'd like to add to this thread.

The comparison between clock on Earth and clock on Jupiter so far is a bit incomplete as it only takes into account the difference in the respective Planet's gravitational fields.  In other words, if all else is equal a clock on Jupiter would run some 20 nanoseconds slower per sec than the clock on Earth.  However, all other things are not equal.  Jupiter orbits further from the Sun than the Earth does.  This means that not only is the Earth deeper in the Sun's gravitational field, it has a greater orbital speed.  These two factor both add up to cause a clock sharing an orbit with the Earth around the Sun to run slower than one sharing Jupiter's orbit.

When you factor this in, it turns out that the clock on Jupiter runs only ~7 nanoseconds per sec slower than the Earth clock when you do a clock to clock comparison.

We do this same combination of gravitational time dilation and time dilation due to speed when dealing with satellites orbiting the Earth and comparing their clock rates to ones on the surface of the Earth.   For lower satellites, the speed factor dominates and the satellite clocks run slow, for higher satellites, the position in the field dominates and the clocks run fast. The dividing line is at an altitude which is equal to half the radius of the Earth.
GPS satellites orbit below this altitude, so they run slower than a clock on the surface.

One last point, Someone mentioned that clocks at high altitude run fast because they are in a weaker gravity field. This, I fear, is misleading as people can take this to mean that it is the local strength of gravity that is the factor that determines gravitational time dilation. This is not the case, It is the difference in gravitational potential.

To illustrate the difference, let's use two different planets to compare clocks, Earth and Uranus.   We will use the " all other things being equal" approach and compare clocks just due to the the planets' gravitational fields.
Doing this, we find that that a clock, according to Gravitational time dilation, will run slower on Uranus than it does on the Earth, However, if we compare surface gravity of the two clocks, Earth's surface gravity is the greater of the two.  A clock on the surface of the Earth will feel a greater gravitational force, but the clock on Uranus will run slower by virtue of being in a deeper gravity well.

144

Physics, Astronomy & Cosmology / Re: Why So Many Ambiguous Labels Of Spacey Stuff ?

« on: 23/10/2016 16:06:19 »

Dearest Spacey Bods ,

As a sheepy I of course luff Space, its like well big and makes for a pleasant view on a cloudless night in a light pollution free zone.

Do you not think that some of the labels attributed to spacey stuff is a little ambiguous and need bringing up to date ?

eg :

Big Bang !...it was not a bang innit ?...it was not an explosion which is what most people think innit ?

The term was originally coined by supporters of the steady state model.  It was meant to be denigrating. The proponents of the expanding universe model decided they liked it and adopted it, Much the way the song "Yankee Doodle" was written by the British to make fun of Americans, and the Americans took it on as a song of pride.

Dark Matter....is it really dark and is it really matter ?

Dark as opposed to luminous, yes.  And the present evidence is that it is likely to be particulate in nature, So unless we can definitely rule this out, matter is as good a term as any other.

Dark Energy ....is it really dark and Is it really energy  ?

Making the two above have similar names makes ewe think they related in some way innit ?

We already had dark matter, so when the accelerated expansion of the Universe was discovered, dark energy seemed the natural choice. Once we actually learn more about it, we may change the name. But then again, we might not.  We still use the term cathode ray tube, when it long been known that "cathode rays" are actually electrons, and we never renamed X-rays even though the X originally stood for "unknown".  It may cause some confusion among the general public,  but as long as those in the field know different, I don't think the similarity in names really manners.

Black Hole ......they not completely black and not really holes are they ?

A number of terms have been used over time "collapsar" and "frozen star", are a couple. Black Hole is just the one that stuck. Some times a name is chosen for the way it flows rather than its accuracy of description. The quark was named from a line in "Finnegan's Wake", and the term google for 10^100 was invented by a mathematician's young son.

Nova a star that momentarily brightens up

Supernova a star that brightens up then explodes !

Hypernova badass version of a supernova

The latter two denote an explosion  the original "Nova" term does not

Nova has a long historical significance,  It means "new" and was used to designate any time a new or "guest" star briefly appeared in the sky.  This was long before anyone even knew what the stars actually were, let alone what was causing the new one. In the same way, asteroids got their name because they were just star-like points of light even in telescopes and "aster" means "star".  But long after we know that they are small rocky bodies, the name persists.

With all the modern info that is discovered, do you not think that renaming things would be appropriate to bring them up to date ?



whajafink ?

hugs and shmishes


mwah mwah mwah

Neil
xxxxxxxxxx

Space is big and very diverse
Glad they called it the Universe

"Uni" means "one", and has nothing to do with size or diversity.  "Universe" basically means "the one unified whole".

Maybe there should be some legislature
About changing the spacey nomenclature[/b]
lol

The IAU decides on the nomenclature( they are the ones who recently came up with the new definitions that degraded Pluto from planet to dwarf-planet.) I think it would take quite a bit for them to change some of these names due to their long time usage, and in some cases, the historical significance.

145

Chemistry / Re: Why do we add elements to the periodic table that decay instantly?

« on: 21/10/2016 22:54:40 »

Thanks to evan, janus and chiral for all your valuable comments.

The point that "heavy" elements are always getting created in supernovae, is one that I realised with a head-smack after posting.  But I didn't to bother to edit, as it was obviously bound to get picked up.

However, going back to the original question, about whether very transient, swiftly-decaying elements should be added to the Periodic Table.  I would say not, because it would make the list of "elements" too long.

If I might cite a comparable example from Astronomy.  The list of "planets" in the Solar System was eight, until the year 1930.  In that year, a new "planet", Pluto, was discovered.  Right from the time of its discovery, there were doubts whether "Pluto", should properly be added as a planet, as it's very small.  However it got accepted until 2006, when the IAU threw it out. 

This was because a lot of new objects were being discovered, like Eris, which is bigger than Pluto. So if you accept Pluto as a planet, you'd have to accept Eris too. And there were more objects of comparable size.  You could eventually end up with a list of 40 or 50 "planets".  Which is far too long.

So the IAU demoted Pluto to dwarf status.  Now astronomers (well, most of them), only acknowledge eight planets on the list. Pluto and the rest are regarded as interesting, but not genuine.

Couldn't this approach be adopted with the Periodic list of elements?  That's to say,  physicists and chemists, should only recognise 92 genuine elements, the rest being merely interesting?

Because half-life doesn't make a good parameter by which to judge whether something is an element or not.  With Pluto, we didn't have a clear cut definition for what a planet was until the IAU decided on the most recent definition.

We do have a good definition for element.

Besides, using half-life would not be consistent with a cut off at element 92.   Neptunium, Plutonium, and Americium all have Isotopes with half-lives that are longer than the longest lived isotopes of a number of elements with atomic numbers less than 92, the shortest being Americium at 7270 yrs. Compare this to Actinium, Radium, Francium, Radon, astatine and Polonium, The longest lived isotope in this group belongs to Radium at 1600 yrs, and the longest lived isotope of Francium (atomic number 87) is a mere 22 min.
Why include it as a "real" element while rejecting higher numbered elements with more stable isotopes?

146

Chemistry / Re: Why do we add elements to the periodic table that decay instantly?

« on: 20/10/2016 02:40:02 »

Do these new "elements" which last only for seconds or microseconds, exist anywhere else in the Universe, except in laboratories on Earth?

If not, I agree with Luke, they're not real "elements" at all. Just something we've fiddled about with, and cooked up locally.  Surely the fact that they disappear so quickly, rules them out as real elements. How can something that vanishes in a split-second, be regarded as anything more than a terrestrial artefact.

Shouldn't a real element stay around for the duration of the Universe, so that it could always be found in the Universe, without relying on a terrestrial source?

Many "Natural" elements do not have infinite lifetimes.  Carbon 14 is constantly forming being formed in our atmosphere and decaying, Uranium is also a "naturally" occurring element which decays, and in doing so creates other short-lived elements. I don't think it makes much sense to say that naturally occurring Radium is not a "real element" just because its most stable isotope has a half-life of just 1600 years.   
As far as these other element existing elsewhere in the universe, If we can make them here on the Earth, then surely they are formed in the supernovae that forged all the other elements including the Uranium we still find in our own crust.   
That's one reason for trying to make these elements on Earth; to learn the rules that determine just what is possible in terms of element formation and to verify whether or not our understanding of what these rules are stand up to experiment.