How are hydrogen and oxygen created?

Hydrogen, the most abundant element in the universe, was created during nucleosynthesis in the first 100 to 1000 seconds of the big bang (13.7 billion years ago) [Linky]. Shortly after that, a few other elements were created from the hydrogen: Helium, Lithium, and Beryllium.

That was it. The universe expanded and cooled too quickly for any more elements to form.

It took around 200 million years for the first stars to form. Those first stars (population III or first-generation) fused hydrogen and helium to create the 88 heavier elements, which were released when the stars died and exploded. Oxygen is one of those elements.

So, there you have it; we are recycled star dust.

Garion's response: "Cooool!"

Why do leaves change color?

"Why do leaves change color in autumn?"

Oh, good, an easier one. :)

Green plants use a chemical called chlorophyll to absorb sunlight, which is needed to metabolize carbon dioxide and water into the sugars the plants need to grow. The carbon dioxide is absorbed from the air (through the leaves, via a process called respiration), and the water is absorbed through the ground.

When fall comes, the days get shorter (less sunlight), which signals the plants to stop producing so much chlorophyll. The plants need to produce less chlorophyll because there's less sunlight and because the winter is generally drier than the rest of the year. So, because there's less sunlight and less water, the plants basically go into hibernation (wrong word, of course) until the days become longer, warmer, and wetter.

Because the plants are not producing chlorophyll, the green color of the leaves fades and the less dominant colors come out. Those colors were there all along, of course, but they were overwhelmed by the green from the chlorophyll.

How do people walk? Part II

"How do people walk?"

The biological answer.

(I will only discuss the muscle contraction part. I'm not a biologist, and there is a HUGE body of research on the biomechanics of walking; I couldn't do it justice.)

When you decide to pick up your foot and move it forward, the brain stimulates a neuron called an alpha motor neuron. This in turn sends a signal down its axon to stimulate the release of calcium (hey, that's from rocks!), which binds to troponin. This chemical reaction causes protiens on the actin (tropomyosin) to change their configuration slightly, exposing a site on the actin to which the myosin head binds.

So, now the muscle is in a configuration such that a thick filament is bound through the myosin heads to a thin filament. The thin filaments are more dynamic than the thick filaments and with the application of a little energy, the thin filament will be "walked" back toward the thick filament. The energy comes from hydrolysis of ATP, which basically transports chemical energy throughout the body.

All of this happens many, many times just to cause your muscles to contract a little bit. To walk, you do this (with many different muscles) over and over and over again.

So, here's a nice little animation of muscle contraction.

How do people walk?

How do people walk (with their legs)?
(K's Answer: "Put one foot in front of the other.")

Okay. There are two parts to this question. 1) physics 2) biology
I'm only going to answer the first part (and really only one very small but important part of that) tonight. I'll try to get to the biology part later in the week.

Basic physics of walking:
1) You all know that we need friction to get anywhere. The ground exerts a frictional force against our forward foot, causing it to stay put while we swing our rear foot around the pivot (hips), advancing our center of gravity; this movement is very much like a pendulum, which I'll get to later.

We can actually write a little expression for the (approximate) minimum coefficient of friction required [linky]:

m = v /[6gL / p² - v²]^1/2

Where m is the coefficient of friction, v is your speed, g is the gravitational acceleration Earth exerts on you (9.8 m/s²) and L is the length of your legs. So, for someone like me who has, ~1 meter long legs, moving at ~2 m/s (4.4 mph), the minimum coefficient of friction required is about 1.4.

That's a unitless number that basically tells you that the frictional force stopping my foot from moving must be 1.4 times the force gravity exerts on me. This is not strictly correct, but I don't have the space to go into it; suffice to say that the amount of force you apply in the opposite direction of your movement must be no larger than the frictional forces. The coefficient of (static) friction only makes sense in this context: when the frictional and applied forces are perfectly balanced, just before your foot slips.

As I try to go faster, I exert greater forces that attempt to cause my feet to slip, and I need a greater coefficient of friction (or more appropriately, the frictional forces need to be higher to keep my feet from slipping, which requires a greater coefficient of friction). If I try to walk on ice, I cannot move very fast because the coefficient of friction is so low that the forces required to move my feet faster tend to easily overwhelm the frictional forces attempting to keep my foot from moving and I slip (and then I usually fall).

I'll talk about the pendulum-like behavior of our bodies next time, when I also get to the biology of walking.

How do rocks create everything? or do they?

First question:

"How do rocks create everything? or do they? I mean everything not animal or person."

He is not going to make this little experiment easy!

First, I'm going to assume he means on the Earth. Bad assumption, I know, but I've got to start somewhere... ;)

First, let's define a rock. Wikipedia has a decent definition. A rock is a naturally occurring aggregate of minerals or mineraloids. A mineraloid is a chemical substance that doesn't actually exhibit a crystalline structure, but perhaps would under different circumstances. Think opal or obsidian; amorphous structures that, in large aggregates, are often considered rocks.

Okay, so a rock is basically a (naturally occurring) collection of minerals. For now, I'm not going to go into how rocks themselves are formed. Let's explore how rocks (minerals and aggregates of minerals) "make everything."

• Plants: Plants require a certain subset of minerals (actually, a certain subset of mineral-forming elements) to grow. There are about 13 elements that form minerals of various kinds that the typical plant can use. This site has a good description of which mineral-forming elements plants use (by absorbing the water into which the minerals have dissolved). I'm going to list the mineral-forming elements and then move on (there's just not enough room to discuss each element--follow the link above if you're interested). All of the minerals come from the soil, which comes from rocks.

1. Nitrogen (N)
2. Phosphorus (P)
3. Potassium (K)
4. Calcium (Ca)
5. Magnesium (Mg)
6. Sulfur (S)
7. Boron (B)
8. Copper (Cu)
9. Iron (Fe)
10. Chloride (Cl)
11. Manganese (Mn)
12. Molybdenum (Mo)
13. Zinc (Zn)

• Building materials: Nearly every kind of building material you can think of utilizes rocks in one form or another.

1. Portland cement is the most commonly used cement in the industrialized world, and its basic components are often used unprocessed as a cheap cement. Portland cement is made up of calcium oxide, silicon oxide, aluminum oxide, ferric oxide, and magnesium oxide is specific concentrations. The minerals are usually quarried from local rocks.
2. Drywall (wallboard, greenboard, etc.) has an inner core made up of gypsum (CaSO4 * 1/2 H2O), calcium sulfate.
3. Shingles, roofing tiles, etc. Many materials used to keep the interior of a home or building are made from minerals of one kind or another. Much of Switzerland has houses with slate roofs, the common shingles you see on most houses (in the west anyway; I don't know anything about the east) are made from tar, fiberglass, and minerals of the desired color. The "mexican" roofing tiles are made from clays and other minerals and then baked.
4. Bricks, cinder blocks, flooring tiles, etc. are generally made of either clays or ceramics, both of which are formed from minerals, which (of course) come from rocks. And don't forget the grout which is a fine-grained cement which often has sand and sometimes very fine gravel mixed in.
   
5. Sinks, bathtubs, etc. are often made of ceramics or other mineral-bearing materials.
   
6. Counters and tabletops can be tiled (with grout) or made of whole slabs of rock.
7. Windows are made of glass (there are many different kinds of glass, many of which contain silica), which is an amorphous solid, rather than a crystalline solid. However, the minerals that are melted and quenched to make the glass almost always come from rocks.
8. Lightbulbs are also made with glass and often metal.
9. Wood, paper, etc. are made from plants that require minerals to grow.
10. Nearly all metals are smelted from mineral ores. Aluminum and brass fixtures, iron pipes, copper pipes, door knobs, electrical wires, nails, screws, bolts, etc. all come from ores (or recycled metals, which originally came from ore).
11. I'm sure I've missed a million things.
    

• Personal Hygene/makeup: Lipstics, makeups, toothpastes (hydrated silica--opal, calcium carbonate--chalk, titanium dioxide) , etcetera, etcetera, etcetera all often have minerals as part of their basic composition, often for coloring or sparklies (mica) in the makeup.
• Dishes, flatware, silverware, cookware, etc: China, ceramic, glass, metal, clay, etc. are all made of minerals or smelted from minerals or somehow derived from rocks.
• Magazines: That shiny paper used in magazines? it's made by coating paper in clay.
  
• Electronics: The metals in all electronics are originally derived from ores (rocks). The glasses used in computer displays, etc. are derived from minerals. The silicon used in the chips is derived from rocks. Solar panels, cameras, radios, etc., etc., etc., all contain silicon and metals, which are both derived from rocks.
• Pigments: Many inks and pigments are made by crushing certain minerals and mixing them into a suspension. Those that don't come from minerals come from plants (which use minerals to grow...blah, blah, blah).
  
• Everything else, practically. About the only thing that I can think of that doesn't come from minerals directly or through one generation or so is petroleum (and therefore plastics). Petroleum (etymology: "rock oil") is plant and animal matter that's been heavily altered by very high pressures and temperatures for very long times. At some point, one has to question if it hasn't changed so much that it's no longer even close to being similar to its original source. Of course, it's pumped out of the ground where it is intimately mixed with rocks... Water, atmosphere, and a few other things are also examples of substances that are removed from rocks by multiple-generations (although many parts of the atmosphere are derived--sometimes directly--from rocks). It really is true that if it can't be grown or hunted, it must be mined [linky]
  

Okay, I got lazy and didn't want to dig up more examples of how "rocks make everything." I also got lazy and didn't want to add more links. I'll probably come back here and insert reference links when I have a little more time.

Introduction

So, G and I are going to discuss science. He's going to ask me a question, I'll answer it, and I'll post the question and answer on this blog.

--G
--M