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Remember: I need homework turned in within a week of its due date (unless prior special arrangements have been made).
Announcements
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.
We will discuss the video in class; here are some of my thoughts, “for the record.”
Comments on Climate Changes Video
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.
*Or at least we’ve not observed them not to hold.
Most climate changes (ice ages, for example) seem to follow cycles with long (in human terms) periods, such as tens of thousands of years.
*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.
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.
pictures in this section “borrowed” from http://www.cotf.edu/ete/modules/msese/dinosaurflr/orbital_change.html
Another is the change of tilt of axis of rotation, with a period on the order of 40,000 years.
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.
Remember, it’s this tilt that gives rise to the seasons.
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 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.
The most recent ice age correlates well with these cycles, called “Milankovich Cycles.”
Here’s a good web page for learning about these cycles:
http://www.cotf.edu/ete/modules/msese/dinosaurflr/orbital_change.html
.
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.
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)
Got to here, January 2008.
Let's do a little experiment on matter...
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.
http://www.plasmas.org/photo-space.htm
The things they teach kids these days!
Actually, most matter in the universe exists in the plasma state…
spacescience.org
Plasma.
…and that big TV you want really badly right now might be a plasma TV.
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.
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?
Let’s next consider something I brought up last lecture…
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
You probably learned in grade school that a force is a push or a pull.
What is a force?
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 rangerelativestrength
comments
strong10-15 meters
1nuclear only
electromagnetic
infinite 10-2 (0.01) shielded
weak10-18 meters
10-7
(0.0000001)nuclear only
gravitational infinite10-38
(0.lots of zeroes 1)additive
The strong force holds neutrons and protons together in the nuclei of atoms.
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).
http://www.lbl.gov/abc/wallchart/chapters/02/2.html
The Strong Force
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 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 Electromagnetic Force
+ + -+
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.”
It is observed that some nuclei are unstable and decay spontaneously (radioactive decay).
The Weak Force
We experience gravitational forces every day.
You might have been surprised by how weak gravity is compared to other forces, especially electro-magnetic forces. Why don't electrical forces overwhelm us?
Because of charge shielding. The universe is full of positively- and negatively-charged particles, which shield us from charges further away.
Gravitational Force
Why does gravity seem so powerful?
“Every 12 hours, the entire earth's diameter shifts by up toa foot (0.3 m) due to the moon's gravitational tidal force.”
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…
http://ffden-2.phys.uaf.edu/211.web.stuff/Lichtenberger/main.htm
Actually, the electromagnetic and weak forces have been shown to be different manifestations of the electroweak force...
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.
Keep that in mind while browsing the web.
…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.
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…
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.
If you Google “fifth force,” beware of pseudoscience gibberish.
got here 2010.
