http://www.nearingzero.net (natural020.jpg)
Announcements
 Remember: I need homework turned in within a week of its
due date (unless prior special arrangements have been made).
 In a week or two I will post the grades spreadsheet.
Tacoma Narrows Bridge:
When humans meet nature, nature has the final say.
When operating outside your data range, beware of
extrapolations.
What worked before may not work under new
circumstances.
A lady in this class a few years ago used to be taken to “ride
the bridge” when she was a small child.
Announcements
If you miss a class where a video is shown, you can still turn
in the video report homework.
As soon as you return, check out the video.
You can keep the video for a week.
Turn the report in when you return the video.
If you skip town with the video, you are a bad person. And
you’ll be sorry.
Comments on Climate Changes Video
We will discuss the video in class; here are some of my
thoughts, “for the record.”
The world around you now is not necessarily typical of the
world centuries ago or the world of the future.
The laws of physics hold,* past, present and future, and the
Earth’s climate can change dramatically as it responds to these
laws.
Most climate changes (ice ages, for example) seem to follow
cycles with long (in human terms) periods, such as tens of
thousands of years.
*Or at least we’ve not observed them not to hold.
Keep in mind that tens of thousands of years is the blink of an
eyelash in Earth’s time. More important, I am seeing more
and more reports that major climate changes may occur over a
span of tens* of years—easily within a human lifetime.
As the video illustrates, seemingly small
changes can start feedback loops that
produce dramatic changes in a short time.
*When I first started teaching this class, it was believed that major swings in
climate could take as little as 50 years to happen. Then I began seeing reports that
dramatic changes can take place in as little as 5 years.
pictures in this section “borrowed” from
http://www.cotf.edu/ete/modules/msese/dinosaurflr/orbital_change.html
The video illustrated two of the Earth’s
cycles. One was the change of shape
of its orbit, with a period on the order
of 100,000 years.
Another is the change of tilt of axis of rotation,
with a period on the order of 40,000 years.
Remember, it’s this tilt that
gives rise to the seasons.
The Earth’s axis also wobbles in a circle with a period of about
26,000 years (the video did not mention this cycle).
Now.
13,000 years from now.
If you remember biorhythms (an example of pseudoscience),
you remember how you were supposed to be concerned if
body cycles peaked or “valleyed” at the same time. Similarly,
but this is “real” science, if all Earth cycles “come together,”
the Earth’s climate may undergo unusually large changes,
including ice ages.
The most recent ice age correlates well with these cycles,
called “Milankovich Cycles.”
It is a matter of great current interest (i.e., you can find some
active, lively debates) whether this is a cause-and-effect event
or random chance, and whether previous ice ages also
correlate with these cycles.
Here’s a good web page for learning about these cycles:
http://www.cotf.edu/ete/modules/msese/dinosaurflr/orbital_change.html.
Another important idea brought out by videos is the moving of
the dry belts. If they were to move dramatically over a
decade’s time, there could be immense political and social
upheaval.
http://www.fao.org/waicent/faoinfo/sustdev/EIdirect/climate/EIsp0054.htm
Some say that global warming would be good, because it
would prevent the next ice age that we are moving towards.
Others point out that global warming won’t mean warming for
everyone. For example, if the Gulf Stream were diverted by
changing ocean temperatures, England’s climate would be like
that of Canada or Alaska.
I need help!
I am coordinating one of Missouri’s eight Regional Science
Olympiad competitions.
About 300 students from regional middle
school, junior high, and high schools will
be on campus Saturday, February 18,
for the competition.
I depend on volunteers to supervise over
40 different events.
I need volunteers to assist; could involve
a few hours on the 18th (general-purpose
help not requiring lots of preparation); or
could involve taking over an event.
It’s a lot of fun. Generally not too much work. Your reward for
volunteer work at the Science Olympiad will be warm fuzzy feelings
and plenty of free food.*
Please e-mail me if you might be interested. Also be patient if I don’t
get back to you immediately.
Some events where I need someone to “take over:” Compute This,
Dynamic Planet, Forestry, Meteorology, Optics, Water Quality, Robot
Arm, Thermodynamics.
*Except I would “trade” your running an event for either your Issue or one Lab.
Now back to our discussion of matter…
http://www.nearingzero.net (nz027.jpg)
Let's do a little experiment on matter...
Got to here, January 2008.
That little experiment showed us something about the states
of matter (you were probably taught they are solid, liquid,
gas).
Solids exist when there is not enough thermal
energy ("heat") to break the chemical bonds
between molecules.
Each piece of a solid has its own shape and volume.
In liquids, molecules are only loosely held
together because there is enough thermal
energy to break lots of bonds.
Liquids have a definite volume but not a definite shape.
When enough thermal energy is added to a
liquid to cause molecules to go flying around,
the liquid boils and becomes a gas.
Gases have neither definite volume nor definite shape.
However, the bonds holding individual molecules together may
be strong enough that the molecules retain their identity (such
as water molecules when they boil).
The nice pictures came from http://www.chem.purdue.edu/gchelp/atoms/states.html
These days they
teach middle school
students about a
fourth state of matter.
Plasma.
The things they teach
kids these days!
spacescience.org
Actually, most matter in the
universe exists in the plasma state…
…and that big TV you want really
badly right now might be a plasma
TV.
http://www.plasmas.org/photo-space.htm
Before the days of plasma TV’s,
when my then 7th grader came
home from school wondering if
any examples of plasmas could
be found on earth, I suggested
he look at the fluorescent lamps
in school.
He was rather unhappy about that. He wanted me to tell him
that plasmas were rare and not found on earth.
Howstuffworks shows you how fluorescent lamps work. You
can also search for plasma TV information.
Now they’re telling us there’s a fifth state of matter!
Anyway, back to my matter experiment… The experiment
involved a "physical" change. No chemical reaction took place.
If left standing, the components I mixed together will separate
back out.
Two very highly-respected friends of mine (a biochemist and a chemist at Mizzou) argue that
the distinction between chemical and physical reactions is arbitrary and meaningless. It is hard
to throw away prejudices acquired in grade school, but they make a strong argument.
When I mix paper and oxygen in a hot environment (454 F?)
a chemical change takes place. Molecular bonds break and
new ones form. I can sit and watch the ashes all day but the
paper will never "separate" itself back out.
I've mentioned chemical and physical changes. When do
nuclear reactions take place? We'll get to that later.
I've used the word force quite a few times in the discussion
today…
…and force is one of the most mis-used terms in the journalist
vocabulary (often used to mean “work,” “power,” “energy”,
“impulse,” and lots of other precisely-defined physics terms…
…so let's talk about forces.
Define “force.” A simple phrase or sentence is sufficient. Write
your definition on a piece of paper and turn it in when we take
a break.
Let’s next consider something
I brought up last lecture…
Like-charged particles repel. Unlike-charged particles attract.
You were taught somewhere in your K-12 education that
atomic nuclei contain positively charged protons. What holds
the nucleus together?
A brief one-sentence answer will suffice. Turn your response in
during break, or before the end of class.
Physical Science:
Force and Motion
Forces
What is a force?
You probably learned in grade school that a force is
a push or a pull.
A more sophisticated definition says that a force is something
that causes an acceleration. I'll come back to that idea in a
bit.
But first, let's consider the kinds of forces that exist in nature.
There are only four. Here is a table with their names, ranges,
relative strengths, and some comments.
force
range
relative
strength
strong
10-15
meters
1
nuclear only
electromagnetic
infinite
10-2 (0.01)
shielded
weak
10-18
meters
gravitational
infinite
comments
10-7 (0.0000001) nuclear only
10-38
(0.lots of zeroes 1)
additive
The Strong Force
The strong force holds
neutrons and protons together
in the nuclei of atoms.
http://www.lbl.gov/abc/wallchart/chapters/02/2.html
It is very strong, so it overcomes the repulsion of positively
charged protons. It is very short-range, so it works only in the
nucleus, and mostly between particles which are in contact
(that's how short-ranged it is).
Electrons don’t get close
enough to any particle to
experience the strong force.
A nucleus made only of
protons would fly apart
because the strong force
couldn't hold all the protons
together.
If you add in some neutrons, the strong force can hold a
nucleus together. In a sense, neutrons act like "glue."
The Electromagnetic Force
The electromagnetic force results in attraction and repulsion of
objects with unlike and like electrical charges.
+
+
+
-
It is quite strong, and extends infinitely far in space. However,
a charge can be shielded (i.e., “neutralized”) by nearby
charges of opposite sign. Shielding tends to “counteract” the
long-range nature of the force.
+
+
+
-
+
Notice that there are no separate electric and magnetic forces.
Electricity and magnetism are like two sides of the same coin.
Several classes from now we will see how this works.
The Weak Force
It is observed that some
nuclei are unstable and decay
spontaneously (radioactive
decay).
It turns out our theories cannot explain the nuclear decay and
radioactivity without invoking another force. It is weak
compared to all forces except gravity, and the shortest-ranged
of all the forces, hence the name “weak force.”
Gravitational Force
We experience gravitational forces
every day.
You might have been surprised by
how weak gravity is compared to
other forces, especially electromagnetic forces. Why don't electrical
forces overwhelm us?
Because of charge shielding. The universe is full of positivelyand negatively-charged particles, which shield us from charges
further away.
“Every 12 hours, the entire
earth's diameter shifts by up to
a foot (0.3 m) due to the moon's
gravitational tidal force.”
Why does gravity seem so
powerful?
Because it is additive and infinite in range.
Any two objects with mass attract each other through the
gravitational force. In contrast to charged particles, all objects
with mass exert an attractive force on all other objects with
mass. The earth's large gravitational force is a result of the
summation of gravitational forces exerted by all of its particles.
The Grand Unification Theory…
The idea of a GUT
seems to attract many
people who think they
can explain it all.
Naturally, when their
ideas don’t get accepted,
it’s because of some
grand conspiracy against
them.
http://ffden2.phys.uaf.edu/211.web.stuff
/Lichtenberger/main.htm
Keep that in mind while
browsing the web.
Actually, the electromagnetic and weak forces have been
shown to be different manifestations of the electroweak
force...
…so you might be justified in saying there are only three
fundamental forces in nature...
…but for now let’s say our four forces are all that are needed
to explain the universe as we know it. There are no more or
no less.
got here 2010.
Don't let anyone invent some new force with a fancy name
and get you to invest in his (or her) new invention which will
revolutionize the world. All it will do is suck up your money.
About 1986, some distinguished physicists thought they had
found experiments which necessitated a fifth force. To
understand their work, we need to revisit the idea of mass…
If you Google “fifth force,” beware of pseudoscience gibberish.