Tale of Two Rivers
Blue Spring sample Attendance Sheets below depict how far up into the
Run that the dark waters of the St. John's River come on several sample
days. What characteristic(s) is there in the dark River water that causes
it to come up into the Run? Why does the dark water extend farther up
into the Run on some days more than on others?
your Journal, write down all the possible reasons you can think of to
explain why the dark water moves to different points in the Run from day
to day. After you've done this then conduct the experiment below. You
can revsit your Journal again after the Experiment.
Activity gives you an experiment to explore how water of one temperature
interacts with water of a different temperature. The different temperature
waters are distinguished by using food color.
St. Johns River
Blue Spring Run water
Wayne's Attendance Sheets
(Click on image to enlarge and print)
As you look at the sample attendance sheets
here, focus in on Ranger Wayne's drawing of how far the dark water
comes into the Run. Find the sheet where the dark water comes in
the farthest, and find the sheet where the dark water comes in the
least. Now look at the River water temperature data for those two
days. Which sheet shows the warmest River water temperature? The
- 2 clear glasses
- A small bowl or
- Tap water
- Food coloring (See
color caution below)
- A spoon
- Paper or old towels
for clean up
- A clock or watch
with second hand so you can time 15 seconds
In this experiment you are going to be using food coloring, which can color
fingers, clothing, the carpet, your dog, the kitchen counter, etc. This
experiment should not be messy, but accidents can happen. Wear old clothes
or an apron and work over the sink. Clean up with paper or old towels instead
of the good kitchen towels.
- Put about 10 spoonfuls
of room temperature water into the small bowl. Add about 10 drops of
food coloring. You can use any color--we used blue. Mix the water and
the food coloring well.
- Fill one of the
glasses with very cold water.(If you use ice to chill it, be sure to
remove the ice cubes before starting this experiment). Fill the second
glass with hot water from the faucet. Place both glasses in the sink,
or someplace where they will not be disturbed and where it won't make
a mess if you spill some.
- Place the bowl
with the food coloring in the sink or near the glasses. Fill the spoon
with colored water and VERY GENTLY add the colored water to the glass
of cold water. Be sure you don't pour the coloring in. Instead, slowly
lower the spoon into the water and then gently pull it out from under
the coloring. You do not want to stir or disturb the water any more
than necessary. Watch carefully and observe what happens for about 15
- Now do the same
thing with the glass of hot water. Being very careful to gently release
the food coloring into the hot water. Again, watch for about 15 seconds.
Compare the two. With both glasses, the coloring will begin to mix with
the water, but there is a noticeable difference. With the hot water,
the coloring will sink quickly towards the bottom. Some of it will mix
with the water along the way, but most of it winds up near the bottom
of the glass. With the cold water, the coloring tends to stay towards
the top and slowly begins to drift downwards. Even after a minute, both
the hot and cold water will still have areas where the color is concentrated
and areas where the water is clear.
Once we understand
and think about hot and cold water, this makes good sense. One spoonful
of cold water weighs more than one spoonful of hot water. Cold water is
denser than hot water and it tends to sink. When you put the colored water
into hot clear water, the coloring sank towards the bottom because it
was cooler and denser and heavier. This denser, heavier cool colored water
displaces the hot clear water. As the coloring warmed up, its density
was nearer to that of the hot water, letting some of it mix upwards.
When you put the colored water into cold clear water, it tended to float
near the surface because it was warmer and less dense. The warmer colored
water floats, just as cooking oil does on the cold clear water. Both are
less dense than cold, clear water. As the colored water cools down, its
density becomes more like that of the cold clear water around it and it
is easier for it to mix.
- From the River
and Run temperatures on the Attendance Sheets, which experiment, #3
or #4 above, do you think most closely simulates the conditions at Blue
Spring? Discuss how the results of that experiment apply to the question
of why the dark River water comes up into the clear Run water.
If you have
laboratory equipment (thermometer, hot plate etc..), try using waters
of a specific temperature to simulate conditions at Blue Spring. For instance,
look at temperatures noted on one of the Attendance Sheets above. Make
the glass of hot clear water the same temperature as the Run. Then make
the colored water the same temperature as the River . Do your results
with these specific temperatures differ from the experiment in Step 4
This! Journaling Question
- Why do you think
the water of the St. John's River is dark and the water of the Blue
Spring Run is clear?
- What is the source
of water for the Run ? The River?
- What is the length
of the Run? The River?
- Does anything grow
in the Run? The River? Why or why not?
was adapted from Robert Krampf's Experiment of the Week email service)
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