Easy Questions?

[goat starer]

Air rushing into the vacuum caused by the lightning.

The charge of the strike leaves an "airless tunnel" that is refilled by the air around it, and it rumbles as it rushes into the vacuum.

Chatty. I would not presume to question your knowledge of the subject but I had understood that this theory had rather fallen out of favour and that it is generally accepted that lihghtning is caused by a shock wave due to thermal expansion in the plasma in the lightning channel. That is a lot harder to get accross simply.

[Swatopluk]

The easiest way to explain the high tide on opposite sides of the Earth seems to be this: The force exerted is inversly proportional to the square of the distance (greater distance = lower pull).
Let's represent that with arrows of different length pointing into the same direction:
------>
---->
-->
Now let's presume that you "sit" on the middle arrow so it is not moving relative to you. How would the other arrows (representing force or velocity) look to you?
-->
.
<--
That is: If you consider yourself unmoving the other two seem to point into different (opposite) directions. With the seemingly unmoved middle you can associate the solid Earth as a whole. It is pulled towards the moon but on the side of the moon the pull is a bit stronger so everything movable on this side will "run forward". On the opposite side the pull is weaker than average, so movable objects "stay behind" because they cannot "keep up". Free-floating water will follow that. The effect is tiny but because of the great distances involved becoming visible (a few meters tide difference on a distance of 10000 km in theory). In reality the blocking landmasses can both increase and decrease the tide difference from negligible (in enclosed areas like the Mediterranean) to more than 10 m in certain other areas where different effects add.


Churches are among the buildings most often hit by lightning. Is that God's revenge for immoral priests and boring sermons?

[Bob in a quantum-state-of-faith]

Here's a common "easy" question.

Why is the Grass Green?

Quick answer:  'Because the Sky is Blue'.

Can anyone give any actual physical justification for the above answer? 

[The Meromorph]

The grass is green and the sky is blue to stop us walking on the sky by mistake...

[Sibling Chatty]

Air rushing into the vacuum caused by the lightning.

The charge of the strike leaves an "airless tunnel" that is refilled by the air around it, and it rumbles as it rushes into the vacuum.

Chatty. I would not presume to question your knowledge of the subject but I had understood that this theory had rather fallen out of favour and that it is generally accepted that lihghtning is caused by a shock wave due to thermal expansion in the plasma in the lightning channel. That is a lot harder to get accross simply.

Goat Honey, this is science. I have NO idea if that's right or wrong. (See answer about the film and the imps. I'm as sure of that one as I am of the other...) I'm a total wash out on science and math, because my education came during a time that it was permissable to say "she's a girl, she'll never really need it" and I was stupid enough to believe it.

Swato?? Lightning sounds 'like that' when you're right by where it strikes...in the dang bar-ditch waiting for the storm to blow over. (Bar-ditch is a specific style of ditch in tornado and cattle country, made to help keep your cattle from wandering if the tornado takes the fences and gates.) Been there, done that, had the 3 days deafness.

Oh, and the churches question??

Steeples. Churches have nice tall steeples that are usually the highest thing around and that's where lightning wants to go...to the highest point. (Smart churchbuilders put a lightning rod atop the steeple and ground it securely, and by something stone or brick.)

[Swatopluk]

Who made that quote about the terminal irony of churches installing lightning rods? (I always forget that).
Another church steeple effect is that the tower tends to be narrow and needle-like. A broad flat-top is less likely to be hit than a spire.

Concerning the thunder sound, that is probably a function of amplitude too. Our school van-de-Graaf generator (static electricity) made the "electric" sound. At the university a few students constructed one with condensator spheres with a diameter of about 2 m. That one didn't sizzle, it did BANG!

[goat starer]

Why is the Grass Green?

Quick answer:  'Because the Sky is Blue'.

Can anyone give any actual physical justification for the above answer? 

there is one that goes something like this (probably not simple enough but here we go)

grass is green because it contains chlorophyll a green pigment that is able to absorb sunlight and convert it to energy (photosynthesis)

light is a specrtrum of waves with different wavelenghths. Colour perception depends on the wavelength.

In the atmosphere short wevelength light is scattered. Short wavelength light is blue and that is why the sky appears blue. look in any direction and you will see the short wavelength blue light. look directly at the sun (not recommended) and you will see longer wavelength red and yellow light.

As there is an abundance of blue light even when out of direct sunlight. there is an abundance of red light light in direct sunlight. To take advantage of this a green pigment such as chlorophyll is needed to absorb blue and red light. If it were green light that scattered in the atmosphere a different pigment that absorbed green light would be needed and the grass would be blue.


I just made that up!!! perhaps a scientist can tell me if it is complete gibberish. 

Chlorophyll absorbs light best in the red

[Bob in a quantum-state-of-faith]

Why is the Grass Green?

Quick answer:  'Because the Sky is Blue'.

Can anyone give any actual physical justification for the above answer? 

I just made that up!!! perhaps a scientist can tell me if it is complete gibberish. 

Chlorophyll absorbs light best in the red

I bolded your last sentence, because this is EXACTLY right!

The shorter wavelengths (blue) tend to scatter, rather than pass directly through the atmosphere, especially ultra-violet (which we can't perceive directly).

Green pigmented objects are green because they are REFLECTING green light.  In this case, Blue and Yellow (the reflecting colors, red being the 3rd one in the REFLECTING spectrum.  In the transmissive spectrum, the colors are Cyan, Green and Magenta-- such as you'd seen on a transparency, or on your PC monitor).

So, a plant will ABSORB the red colors, but reflect all the rest.

If it absorbed ALL the colors, it would be overloaded with energy, and get sunburn. But, by absorbing just the red, it gets sufficient energy to break apart CO2 and H2O (photosynthesis) various parts.

A simple general equation for photosynthesis is:

6 CO2 + 12 H2O + light → C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy → glucose + oxygen + water

Because of the blue-scatter (due to absorption of light energy by free-oxygen, if I remember right), red and yellow would be the best wavelengths to absorb.  red AND yellow would be too much, so yellow (and any residual blue) is reflected (making the leaves GREEN), and only the red is kept.

Thus, due to the BLUE SKY, the GRASS IS GREEN. 

[Swatopluk]

To add another bit: Plants contain carotenoids (yellow-orange) as protectors. They absorb light in "dangerous" wavelengths and additionally capture free radicals that are a byproduct of photosynthesis. In fall the chlorophyll is degraded by the plants, so only the carotenoids remain (=> leaves turning yellow).
Actually we have to isolate chlorophyll to prove it to be green. If it were blue it could result in a color-mix: blue + yellow = green.
We do not notice it but the sun emits quite a bit in the green part of the spectrum but not enough to "overpower" the yellow impression. Interestingly there are no true green stars (at least non yet found), while about everything else can be found from blue-white to dark red.

[Sibling Lambicus the Toluous]

Here's a puzzler that my Dad would ask me when I was little (partly because I'd laugh at all the homonyms, I think):

If you dig a hole, you have a whole hole.  But if you fill it halfway full, you'll have half a hole, but still a whole hole.  How can that be?

[Bob in a quantum-state-of-faith]

Here's a puzzler that my Dad would ask me when I was little (partly because I'd laugh at all the homonyms, I think):

If you dig a hole, you have a whole hole.  But if you fill it halfway full, you'll have half a hole, but still a whole hole.  How can that be?

But, wait! it gets better 

If you want to REMOVE something from your yard, normally, you'd dig it up.

When you dig up the hole, you're left with---an even bigger hole!

So, to REMOVE a hole, you must ADD something!  Subtraction by addition? 

[goat starer]

So, a plant will ABSORB the red colors, but reflect all the rest.

Chlorophyll absorbs blue light best but it is very good at absorbing red light also. My explanation above explains why this is important as many plants do not get direct sunlight and must rely on scattered blue light.

here is the graph



the hole thing works for a mound too. It works for almost enything that does not have a frixed quantity but workd particularly well for holes as they are an absence rather than a presence (which alows the second point). In anything that assumes a shape regardless of size and has the same name regardless of size subtraction and addition do not change the name.

[Swatopluk]

Concerning the hole: A notorious case of an absence having a name of its own and therefore easily mistaken as "something".
Similar: cold(ness), darkness, vacuum (if you don't go into quantum mechanics/dynamics).
Additionally it is an indivisible. i.e. any part being essentially being the same as a whole (the difference between extensive [size-dependent, e.g. mass] and intensive [unchanged by division, e.g. temperature] characteristics).

----

Can a photon see itself in a mirror in front of it?

[Griffin NoName]

For Sibling Chatty .... (non-sciencey) What are the top five fibs parents tell their children? (no googling!!).

[Sibling Chatty]

You were planned,  It won't hurt a bit, Not until we were married, Of course Mum/Dad loves grandparent on opposite side of family, You can be anything you want to be if you work hard enough.