Friday, 31 January 2014


Class summary:
January 28th and 29th, 2014
  1. General review of last class' lesson, including answering the following questions:
– Q1. what are some properties of water?
– Q2. what are some of the the main usages for water, worldwide?
– Q3. What are the main differences between saltwater and freshwater? 
– Q4. where is most of the world's freshwater pumped from?
– Q5. where is most of it the world's freshwater found?
– Q6. why haven't the world's freshwater reserves been exhausted over the centuries?
– Q7. how well do we take care of our freshwater?

     2. Two demonstrations

     3.  Variations of the water cycle

     4. Water in different sections of the water cycle

     5. Energy changes within the water cycle

1) Last Class's Overview
Naturally, I'd recommend attempting to solve the above questions on your own; however, if you are indeed struggling or desire to check your answers, an answer key is found below.

– A1. There are several possible answers; however, the two primary properties of water discussed last class was that water dissolves things such as salts (solvent), water molecules like to stick together (viscous), and that there exists space between water molecules. In terms of the latter property, the space between water molecules was the main concept behind the "10 + 10 ≠ 20" experiment. Here, students added up ten milliliters of water and ten milliliters of ethanol into a jar, didn't equal a total of 20 milliliters because ethanol molecules—often around two milliliters of the ten—ultimately occupied less space (well, more of the space, really) by resting in the space between water molecules.
– A2. The main usage of water is growing food, whether it's for irrigation or hydrating animals that'll later be processed for their meat.
– A3. There are several possible answers; however, the primary difference discussed last class was the difference in densities between the two.
– A4. Most of the freshwater consumed comes from natural underground reservoirs pumped to the surface.
– A5. Most of the world's freshwater is located in the world's poles (namely, the South Pole). A fun fact pointed out by Mr. Pro was that, due to the age of said icecaps, it is possible for scientists to dig down into the ice (almost three kilometers from sea level at certain points!) and produce samples, thus allowing us to learn about differences between water from millennia ago and water from modern day.
– A6. The reason why freshwater hasn't run out is that water is one of the main concepts of the water cycle—namely, evaporation. Essentially, water, be it pure or not, will always rise as water vapor to form clouds (and from there condensate, precipitate, etc.) as water alone—it'll leave behind any impurities like salt, waste, or other chemicals. Thus, freshwaterwater will never run out (at least for as long as water isn't consumed so fast that the water cycle can't keep up).
– A7. To put it briefly, not very well. A few main points brought up were the melting of the world's icecaps, thus causing considerable portions of the world's freshwater to merge with saltwater (thus becoming saltwater itself), and the disposal of garbage in rivers.

2) Demonstration One – water purifier
We were shown how to use fairly average materials in order to extract freshwater from saltwater by taking advantage of the water cycle.

Essentially, a container (preferably with somewhat steeper sides and without any major holes or gaps), filled with impure water, was placed out in the sun. The container was covered with a clear plastic with a reasonably small rock over the center of the plastic, and also in the center but under the plastic was another container.

Here's how it works: the plastic that covers the container allows light through, thus enabling the occurrence of evaporation. As mentioned earlier, because evaporation generally leaves all impurities behind, only the clean water rose and condensed on the plastic overhead. Because of the rock causing a minor depression in the plastic, nevertheless, the newly-condensed (and more importantly, clean) water slowly moved it's way towards the center of the plastic—later dripping from the center point onto the second container below the plastic. Thus, after some time, most of the unclean water in the larger container would have been purified into the smaller container.

2) Demonstration Two – density, and. . . water?
This demonstration involved comparing the densities of two clear liquids by testing whether candle wax floated on them or not. Although the immediate answer from most students was that the back glass was saltwater as the object floated and the front glass was freshwater because it didn't, we didn't quite realize water isn't the only clear liquid—what about alcohol, vinegar, or gasoline? Overall, not only was the main point of the experiment to remind us of density, but also to bring to light that clear liquids aren't always what they seem.

3) Is there only one variation of the water cycle?
To put it briefly, no. The water cycle, most commonly interpreted through "rain (precipitation) --> ocean --> water vapor (evaporation) --> clouds (condensation) --> rain," is not at all the only variation of the cycle—in fact, it's only just the most common.

During class, we used this document as a guide to think of multiple new variations of the cycle.

4) Water during different sections of the cycle
We answered some questions in groups using our textbooks regarding, for the most part, precipitation and humidity. They were: 1. explain humidity, 2. explain how precipitation forms, 3. explain kinds of precipitaiton, 4. explain global differences in precipitation. Alternatively, you can take a look at the document them here.

A few student exemplars can be found here.

1) Explain Humidity

2) Explain how precipitation forms
3) Explain the Kinds of Precipitation
4) Explain global differences in precipitation

  • What is it?
  • How do we measure it?
  • Why are there different forms of precipitation?
  • How can we imagine precipitation forming?
  • What are they?
  • How are they different?
  • Look at the map and summarize differences in precipitation based on locations in the world.

Spaulding, Sandy Book, pg 391-392
Spaulding, Sandy Book, pg 402
Spaulding, Sandy Book, pg 403
Spaulding, Sandy Book, pg 405

Specific humidity is the amount of water in the air measured in grams of water per kilogram of air.  Relative humidity, expressed in percent, is how much water is in the air compared to the maximum possible value.  
Humidity is measured using two thermometers, one wet and one dry.  The difference in the temperature of the thermometers can be used to determine the humidity.
Precipitation forms when water/ice molecules stick and clump together.  This is more likely to occur as water in the air cools at higher elevations.  
Drizzle is very small drops of water slowly falling close together.
Rain, however, is large and further apart.
If raindrops freeze on the way down, it forms sleet, which is ice.
Freezing rain occurs when rains freeze upon hitting the surface.
Hail forms in the atmosphere as rain falls through a layer of cold air and freezes.  It is in the forms of spherical ice.
Snow is ice that forms in the clouds and then falls all the way to the ground.
Most of the places with lots of precipitation are in the Tropics.  This is because the tropics receive the most sunlight and therefore have the most evaporation of water and the most rain.  
The poles tend to have little precipitation because they receive very little sunlight.  With little sunlight, there is less evaporation of water and therefore less precipitation.  Also, a lot of the water is in the form of ice, and it takes much more energy for it to evaporate.
The Temperate regions tend to have moderate precipitation.

Above is Mr. Pro's answer key.

5) Energy changes within the water cycle
Returning to our water cycle diagrams made in our previous class, each person labeled each section or change in their diagram with that section's respective energy change.

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