Friday Feb. 16, 2007

The graded quizzes were returned in class today.  Please check your quiz carefully for errors.
You can check the progress being made grading the 1S1P Assignment #1 reports at this link.
Here's an example of a grade that you might see when you get your 1S1P report.

The first number refers to the information content of your report.  You could earn up to 8 pts for content on Topic #1 (The Earth's Changing Climate) reports (the only ones graded so far).  The more specfic details and information that you include in your report the higher this grade will be.  The second number is the quality of the writing.  To receive a high writing grade your report should be your understanding and explanation of the material (it should be written in your words, you should just paraphrase the discussion in the textbook), should be free of spelling mistakes and grammatical errors.  The person above received 11.5 out of a total 15 pts possible.  Don't think of this as a percentage grade.  You can earn up to 45 1S1P pts during the semester.  The person above has 45 - 11.5 = 33.5 pts left to go.  As long as this person keeps writing and turning in reports in future assignments he or she shouldn't have any trouble reaching the 45 pts goal.
First sometime the depends on specific heat, something we covered on Monday.  The surface of the earth is largely made up of water (oceans) and soil.  Water has a larger specific heat (heat capacity) than soil.  Oceans are slow to warm in the summer and slow to cool during the winter. 


Oceans moderate the climate.  The city above on the coast has a 30o F annual range of temperature.  The city further inland (assumed to be at the same latitude and altitude) has an annual range of 60o F.  Note that both cities have the same 60o F annual mean temperature.  Proximity to land or water is one of three or four factors that determine a region's climate.  Latitude and altitude also play important roles.  This is discussed in Chapter 3 and will probably be a topic on a future 1S1P assignment.
A very cold and dry air mass has moved over the eastern portion of the United States.  We saw on a satellite photograph that showed as this air moved off land and out over the Gulf of Mexico and the Atlantic Ocean a thick layer of low level clouds formed. 

This is a pretty good example of a phenomenon called the "Lake Effect."  The Lake Effect was in the news a week or so also.  Cold dry air blowing across the Great Lakes dumped upwards of 10 feet of snow on parts of New York.


You wouldn't expect cold dry air to produce record amounts of snow and it doesn't.  The cold dry air is modified as it moves over warmer lake or ocean water.  Heat and moisture from the water flow into the cold dry air mass.  The heat warms the air and makes it bouyant.  If the rising air is moist enough and cools enough, clouds and precipitation can result.

If you add energy to a material it will usually warm. 

Temperature provides a measure of the average kinetic of the atoms or molecules in a material.

You can think of heat as being the total kinetic energy of all the molecules or atoms in a material.  The next figure might make the distinction between temperature (average kinetic energy) and heat (total kinetic energy) clearer. 


A cup of water and a pool of water both have the same temperature.  The average kinetic energy of the water molecules in the pool and in the cup are the same.  There are a lot more molecules in the pool than in the cup.  So if you add together all the kinetic energies of all the molecules in the pool you are going to get a much bigger number than if you sum the kinetic energies of the molecules in the cup.  There is a lot more stored energy in the pool than in the cup.  It would be a lot harder to cool (or warm) all the water in the pool than it would be the cup.

In the same way the two groups of people shown have the same average amount of money per person.  The $100 held by the group at the left is greater than the $20 total possessed by the smaller group of people on the right.

You need to be careful what temperature scale you use when using temperature as a measure of average kinetic energy.  You must use the Kelvin temperature scale because it does not go below zero.  THe smallest kinetic energy you can have is zero kinetic energy.

You should remember the temperatures of the boiling point and freezing point of water on the Fahrenheit, Celsius, and Kelvin scales.  300 K is a good easy-to-remember value for the global annual average surface temperature of the earth.


You certainly don't need to try to remember all these numbers.  The world high temperature record was set in Libya, the US record in Death Valley.  The continental US cold temperature record of -70 F was set in Montana and the -80 F value in Alaska.  The world record -129 F was measured at Vostok station in Antarctica.  This unusually cold reading was the result of three factors: high latitude, high altitude, and location in the middle of land rather than near or surrounded by ocean.   You'll find more record high and low temperature data on p. 58 and p. 60 in Chapter 3 of the text.  Precipitation records are shown on p. 348.  Note that even liquid nitrogen is still quite a bit warmer than absolute zero.


Conduction is the first of four energy transport processes that we will cover.  The figure above illustrates this process.  A hot object is stuck in the middle of some air. In the first picture the random motions of the atoms or molecules near the object have caused them to collide with and pick up energy from the object.  This is reflected by the increased speed of motion or increased kinetic energy of these molecules or atoms (these guys are colored red).  In the middle picture the initial bunch of energetic molecules have collided with some of their neighbors and shared energy with them (these are orange).  The neighbor molecules have gained energy though they don't have as much energy as the molecules next to the hot object.  In the third picture molecules further from the object now have gained some energy (the yellow ones).  The random motions and collisions between molecules is carrying energy from the hot object out into the colder material.

The rate of energy transport depends on the material.  Thermal conductivities of some materials are listed above.  Air is a very poor conductor of energy.  Air is generally regarded as an insulator.  Water is a little bit better conductor.  Metals are generally very good conductors (sauce pans are often made of stainless steel but have aluminum or copper bottoms to evenly spread out heat when placed on a stove).  Diamond has a very high thermal conductivity.  Diamonds are sometimes called "ice."  They feel cold when you touch them.  The cold feeling is due to the fact that they conduct energy very quickly away from your warm fingers when you touch them.

The rate of energy transport also depends on temperature difference.  If the object in the picture had been warm rather than hot, less energy would flow or energy would flow at a slower into the surrounding material.

The next figure shows a demonstration that we didn't do in class.  If the instructor were to open a bottle of something with a strong smell such as glacial acetic acid (acetic acid gives vinegar its characteristic smell) in the front of the classroom, the odor would eventually spread throughout the class room.  This is an example of diffusion.  The acetic acid molecules would be moved through the room by random collisions with air molecules.  In many respects this is like the conduction of heat.  The demonstration wasn't performed because the concentration of the acetic acid in the air, at least in the front of the room, would be high enough to present a serious risk to the instructor and students.



The acetic acid is beginning to evaporate into the air.  Collisions with air molecules would begin to move the acetic acid molecules toward the back of the room.



The instructor has lost consciousness because of the strong odor of the acetic acid in the front of the room. 


The odor would eventually spread throughout the class room.
Convection is the next energy transport process we'll look at.

This definition is as far as we got in class.  The material below was added after class.  We'll review this quickly in class on Monday.

In the picture above the air surrounding a hot object has been heated by conduction. Then a person (yes that is a drawing of a person's head) is blowing the blob of warm air off to the right.  The warm air molecules are moving away from the hot object together as a group (that's the organized part of the motion).

Cooler air moves in and surrounds the hot object and the cycle can repeat itself.  This is forced convection.  If you have a hot object in your hand you could just hold onto it and let it cool by conduction.  That might take a while because air is a poor conductor.  Or you could blow on the hot object and force it to cool more quickly.


Note in the figure above (at lower left) that, because hot air is also low density, it actually isn't necessary to blow on the hot object, the warm air will rise by itself.  Energy is being transported away from the hot object into the cooler surrounding air.  This is called free convection and represents another way of causing rising air motions in the atmosphere (rising air motions are important because rising air expands (as it moves into lower pressure surroundings) and cools.  If the air is moist, clouds can form.)

Note the example at upper right is also free convection.  The sinking air motions that would be found around a cold object have the effect of transporting energy from the warm surroundings to the colder object.