Tuesday, February 26, 2008

Co-op Weeks Four and Five

We spent two weeks covering the topic of "wind" - Week Four focused a little more on global wind patterns, and Week Five continued by talking about local wind patterns.

Weather Unit - Lesson Four

1.  What causes the wind?  One basic cause is that air moves from high pressure to low pressure areas.  We talked about what is happening when you blow up a balloon (there is HIGH air pressure inside the balloon) and then let go of the opening (the air comes out because it is moving from high pressure to low pressure).  The greater the pressure difference, the stronger the wind. 

2.  Wind directions change, but most often the wind comes from one direction more than others - this is the "prevailing" wind pattern in the area.  In general, wind patterns are also related to the moving air cells of heat - cold air sinks, warm air rises.  We looked at a handout showing global wind patterns:

  • In the tropics, winds are usually easterly (from the east) and are called trade winds because of the importance to sailing ships for the purpose of trade - back in the day when trade was dependent on sailing ships, of course.

  • at the equator, there are wind-less regions of low pressure where the air is rising straight up.  These are called the "doldrums" are were to be avoided by sailing ships.

  • at about 30* latitude are the "horse latitudes" - another type of doldrums, that sailors avoided if at all possible.  Here the air currents are coming down.  Without cross winds to move a sailing ship, and with the downward pressure of the air current, ships often had to dump cargo - including horses! - in order to be light enough to move, hence the name.  I did not know this before, although I had heard of the horse latitudes!

  • in the mid-latitudes, the prevailing winds are westerlies

  • near the poles, the prevailing winds are easterlies

3.  We talked very briefly about how wind can be used to generate electricity with wind farms, how it powers old-fashioned windmills, why farmers depend on treelines to cut down on wind erosion, and how the understanding of wind direction and speed is important to pilots and from a historical perspective - to archers.

4.  Another important global wind is the jet stream.  This is a fast-moving wind about 6-7 miles up in the atmosphere.  This is where jets fly, hence the name.  When flying with the jet stream, an airplane can cut its travel time significantly, and when flying the opposite direction, pilots plan their course to avoid the jet stream.  The jet stream  winds can be up to 190 mph!  The jet stream moves weather patterns as well, as it usually divides warm and cool air masses.  There are four major jet streams that travel in a wavy pattern around the globe.  The jet stream over North America brings cooler northern weather to the mid-US when its wavy pattern dips south, and brings warmer, milder southern weather to the northern part of the continent when it stays on a more northern track.  We looked at a handout showing the jet stream and explaining it.

5.  We made and quickly tested a very simple windsock.  We bent wire coat hangers to a square shape and taped a plastic trash bag around that square opening.  Tres simple!!!!  Then we had just enough time to take our white-trash windsocks  outside to see if we could tell which way the wind was blowing.  Sadly - I did not take any pictures.  I was informed the following week that some of the kids had mounted their windbags windsocks in their yards.  Wonder what the neighbors think...  We didn't mount ours, because we live in a wind tunnel, I think.  The prevailing wind at our house is STRONG.  LOL

Weather Unit - Lesson Five

1.  The kids reported on what they'd observed with their windsocks over the previous week, as some had mounted them in their yards or taken them outside at various times.  We talked about the limitation of what a windsock can tell us about the wind - it can indicate the direction and give a sense of how strong the wind is, whether it is gusting or steady - but it really cannot give an accurate speed.  So - next project is to make a simple anemometer.  These are usually made with four cups on a weathervane type of stand, and then you have to count how many times the cups spin over a set time to calculate the speed of the wind.  We have 7 to 9 year olds in the class, and only 40 minutes, so I found a much simpler design of anemometer that we could build ourselves.  We used a protractor, a length of string, and a pingpong ball.  Cut a length of string about six inches long, tape it to the pingpong ball and tape the other end of the string to the center of the straight edge of the protractor.  Voila! An anemometer!    Here is Landon's:

And close-up:

And yes, that string is indeed longer than six inches.  It still works okay though.  Here is the approximate wind speed scale:

  • string/ball hanging at 90* - wind is zero mph

  • at 80* - wind is approximately 6 mph

  • at 60* - wind is approximately 15 mph

  • at 25* - wind is approximately 30 mph

  • I told the kids if it was a lower number on the protractor than 25*, that they should not be measuring, they should be inside because either a nor'easter or a hurricane coming through.  LOL

2.  I handed out, and we discussed the Beaufort scale and how it was developed.

3.  We had a handout listing some local wind patterns, and explaining how sea and land breezes worked, and how anabotic and katabotic winds affect local weather patterns.  (I used this website to make the handout)  We mentioned some local wind names and talked about what they are:  chinooks, nor'easters, haboob, Santa Ana, etc.  I was very disappointed that I had forgotten to bring my picture of the chinook arch to pass around.  I told the kids I'd try to remember it the following week.

And now, if you'll excuse me, I need to get Lesson Six planned!!!


CrossView said...

What fun! My youngest is a hands-on kid so she'd love science at your school! =D

MayTheyBeMightyMen said...

I think we need to do some of this. Very cool!

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