http://www.nearingzero.net (natural020.jpg)

Jan. 9The Scientific

Method

Jan. 11Measurements

Jan. 16no class

Jan. 18Matter and Mass

Jan. 23Climate Changes Video (104 Phys.)

Jan. 25Video DiscussionForce and Motion

Jan. 30Force and Motion

Feb. 1Force and Motion

First Four Weeks Schedule

Lab meets Friday!

“The most incomprehensible fact about the universeis that it is comprehensible.”—A. Einstein

Remember: I need homework turned in within a week of its due date (unless prior special arrangements have been made).

Announcements

After I get all “secret code names” 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.

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. Now I am 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, if all three cycles “come together,” the earth’s climate can 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.

Nearly 500 students from regional middle school, junior high, and high schools will be on campus Saturday, February 25, for the competition.

I depend on volunteers to supervise the approximately 40 different events.

I need volunteers to “take over” a few events (a big undertaking). I need other volunteers to assist (a few hours on the 25th).

It’s a lot of fun. Also work. I am willing to trade homework/lab assignments for volunteer work at the Science Olympiad.Please e-mail me if you might be interested. Also be patient if I don’t get back to you immediately.

I will also be looking for judges at the Mark Twain Elementary School Science Fair on Thursday, February 23.

Now back to our discussion of matter…

http://www.nearingzero.net (nz027.jpg)

Recall that I was talking about the plum pudding model of the atom…

…which didn’t seem to be working too well……so this scientist Rutherford suggested…

…stick your finger in the pudding and see what’s there!

Except instead of using his finger (too big) Rutherford used alpha particles (which we now know to be helium nuclei).

If the plum pudding model is correct, alpha particles will not be deflected by tiny electrons, and only weakly deflected by the smeared-out positive charge distribution.

Rutherford tried shooting alpha particles at a variety of thin metal foils and found this expectation to be “true.”

Rutherford’s co-worker was Hans Geiger (“Geiger counter”).

*“Nothing interesting can possibly happen, but let’s have poor Marsden do it anyway. Ha ha ha...”

Rutherford and Geiger had an undergraduate named Ernest Marsden working for them in 1909. They assigned Marsden the job of measuring the scattering at large angles* of alpha particles by a very thin gold foil.

Indeed, most of Marsden’s alpha particles passed straight through the gold foil.

A few were scattered at large angles.

Some even bounced straight back.

“It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you.”—Ernest Rutherford

USS Washington

15 inch guns

In the Thomson model, electric charge is smeared out over the atomic volume, and minimal interaction is expected between the charged alpha particles and the gold atoms. That’s because there’s no local electric field to deflect a charged particle.

OK, I lied on the previous slide (for dramatic effect). The battleship Washington had a main battery of nine 16-inch guns. I spent a long time looking for pictures of 15-inch guns and shells, with humans in them to illustrate the scale.

Lots of 16-shell pictures, like this one. No 15-inch. But if you see one of these coming at you, are you going to argue about that extra inch?

“It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you.”—Ernest Rutherford

15-inch shell: weight—2700 pounds; muzzle velocity—1570 miles per hour; range—21 miles

Splat!

Scattering experiments “demanded” the model that Rutherford then invented for the atom.

See http://micro.magnet.fsu.edu/electromag/java/rutherford/ for a “toy” to play with.

Expected.

Observed. There must be concentrations of massive, highly charged matter to deflect the alpha particles.figures from: http://www.as.utexas.edu/astronomy/education/spring01/lambert/classnotes9.html

So a “snapshot” of Rutherford’s atom at some instant in time looks like this. -

++++

-

-

-Of course, the electrons and nucleus are very small, but I had to draw them big enough to see.

Rutherford didn’t use the word “nucleus” in describing this model. He used the term “charge concentration.”*

*See http://dbhs.wvusd.k12.ca.us/AtomicStructure/Rutherford-Model.html

Rutherford was confident he had the atom figured out. "The question of the stability of the atom proposed need not be considered at this stage, for this will obviously depend upon the minute structure of the atom, and on the motion of the constituent charged parts."*

In the previous lecture, you probably told me atoms are made of neutrons, protons and electrons. The neutrons and protons are "squeezed" together inside very small nuclei. The electrons "orbit" somewhere outside the nucleus. Protons are positively charged particles, and neutrons are neutral.

http://www.valleystream13.com/Wheeler/science/jan/atom

So your atom looks something like this…

http://www.csmate.colostate.edu/cltw/cohortpages/viney/atomhistory.html

You have a problem here!

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?

We interrupt this lecture to bring you this brief mental exercise…

A brief one-sentence answer will suffice. Put your name on the piece of paper with your response, and turn it in during break, or before the end of class.

So your atom looks something like this…

http://www.csmate.colostate.edu/cltw/cohortpages/viney/atomhistory.html

Did it ever bother you when a science teacher told you that the nucleus was made of neutrons and protons? How can lots of positively charged protons be squeezed together inside a small volume? I thought like charges repel.

You have a problem here!

It is true that matter is made of atoms, which are made of neutrons, protons, and electrons.

Did any of you raise your hand and protest that finding a bunch of protons crammed together is not consistent with “like charges repel?”

It is also true that like charged protons repel each other, like charged electrons repel each other, and unlike charged electrons and protons attract each other. The force between charged particles is called the "electro-static" force; "electro-" for obvious (I hope) reasons and "static" because the force exists between particles when they are stationary (as well as when they are in motion).

+ +

This force must be stronger than the electrostatic force.

What does the fact that atomic nuclei are held together tightly imply to you?

There must be some other force in operation besides the electrostatic force.

The force that binds electrons to atoms is much weaker. That's why you can easily "scrape" electrons off atoms.

The force that hold nuclei together is, in fact, extremely strong. That's why atomic bombs and nuclear reactors are so "powerful." I'll talk about it later.

Atoms can bond together to form molecules or crystals. The bonds that hold atoms together in crystals are a result of the behavior of electrons.

I wonder what role the neutrons in atoms play. It seems now as if they are excess baggage. Anybody ever wonder about them?

The bonds can be very weak, as between oxygen molecules (at room temperature it is far too warm for oxygen molecules to form solid oxygen), or quite strong, as in diamonds.

Environmental IssuesIssue 7: Grain Production

and Beef Consumption

If you choose this Issue, you’ll investigate global grain production and the effect of beef consumption on grain usage.

Let's do a little experiment on matter... (did it last time!)

Remember, Issues 2 and 6 are a single “package,” as are Issues 4 and 5.

As you do these Issues, the text author will refer you to external sources. You might wish to investigate these sources further. I notice one interesting source in Issue 7. Do these sources of information have a particular axe to grind?

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 TV you probably want really badly right now is a plasma TV.

Before the days of plasma TV’s, when my 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.

When I mix paper and oxygen in a hot environment (454 F?) a chemical change takes place. Molecular bonds have been broken and new ones formed. 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.

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.

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.

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