Physical Science, Module 3, The Atmosphere

►Videos we watched for Module 3 
►What we did 2012-13
Play  Quizlet.  Just scroll down and click on Physical, then scroll to find the Module you want.

3.1 Atmospheric Pressure

The atmosphere around us is pressing on us from all sides all the time.  You don't really feel it, but it's there.
This experiment shows that the air in the glass and the air outside the glass is pushing down on the water.  We colored the water blue to make it easier to see, since we had a red candle.  But the red candle kept burning out in the melted wax, so we switched candles, and the only other candle I had just happened to be blue!
At the beginning, the air in the glass was the same as the air outside the glass.  As the candle burned, it used up the oxygen in the glass.  With less oxygen, there were fewer molecules, and the air in the glass could not exert as much pressure on the water as before.  This caused an imbalance.  The pressure outside the glass was greater than inside the glass, which pushed the water up inside the glass.  It only went up so far since there was still a lot of nitrogen in the glass.  The water "made up" for the lost pressure of the oxygen, making the pressure inside and outside the jar balanced.




Our atmosphere is in two general layers, the Heterosphere and the Homosphere.
Heterosphere - The upper layer of the earth's atmosphere, which exists higher than 80 kilometers (50 miles) above sea level.  The composition of the air in the heterosphere depends on the altitude, which causes changes in temperature at different levels.  The concentration of air in the heterosphere is low, therefore we say the air is "thin" in the heterosphere.
The heterosphere is divided into two layers, the thermosphere (the region of the atmosphere between altitudes of 80-460 kilometers) and the exosphere(the region of the atmosphere above and altitude of 460 kilometers).

Homosphere - The lower layer of the earth's atmosphere, which exists from ground level to roughly 80 kilometers (50 miles) above sea level.  The homosphere has about the same composition of gases, regardless of where you are in the atmosphere.
The homosphere can be further divided into three layers - the troposphere (up to about 7 miles above sea level), stratosphere (from about 7-30 miles above sea level), and mesosphere (from about 30-50 miles above sea level).
In reading the text, you will see that the temperature changes with elevation.  Although the troposphere gradually gets colder with higher elevation, the stratosphere actually gets warmer.  This is because of the greenhouse gas (ozone) that is present in the stratosphere layer.  The energy of the gases in the stratosphere is higher than the energy of the gases at the top of the troposphere, causing the molecules to move faster.
Temperature is actually a measure of the energy of motion in a substance's molecules.
 
3.2 The Effect of Changing Temperature on MoleculesWe had a sink of icy water w/ two frozen 2-liters in it, and a sink of very hot water that I'd heated on the stove.
The kids held an empty 20-oz bottle in the icy water for a few minutes to make the air cold inside the bottle.  This slowed down the molecules.  Then they put a balloon over the opening and put the bottle into the hot water.  Immediately the air became hot in the bottle as the molecules moved faster and bounced against the sides of the balloon, inflating it a little.  Then when they put it back into the ice water, the balloon and the bottle contracted.
A lot of people know things expand when they are hot, and contract when they are cold, but they may not know it is the molecules moving faster or slower that causes it.
See this experiment at DonnaYoung.org.

Later as the 8th and 9th graders were writing their lab report, JohnDavid was playing around with the bottle.   He discovered if he put the bottle straight down in the ice water for a minute (upside down), then put it straight down in the hot water, the expanding air made bubbles escape from the bottle even though he did not tilt it.  After a minute, he put it back into the cold water, and as the air contracted, it pulled water up into the bottle a few inches.  =)
Yay, discovery!
A little more discussion about how temperature changes affect the behavior of molecules.  =)

Even though we've learned that cold molecules contract, we know that water expands as it freezes, enabling it to float.  God knows what he's doing, doesn't he?
Imagine if the ice contracted, so that it didn't float.  The ponds and lakes would freeze solid, killing all the life in them.  Oceans would be frozen from glaciers and sea ice sinking to the bottom.
I've challenged the kids to discover whether equal amounts of very hot or icy cold water will make a larger ice cube. 
Try it.  Fill 2 plastic cups halfway to the exact same amount using very hot and very cold water.  Use a measuring cup for accuracy.
Leave a comment here and tell me what happened!