Does Fresh Water Float?
In our Updates,
Biologist Cathy Beck has mentioned that fresh water will float on salt
water. But why? With these simple experiments, you can explore how and
why this happens, and what it means for the buoyancy of things in salt
and fresh water:
- 3 Tall
clear glasses that can hold at least 8oz. of liquid
- Food Coloring
- Eye Dropper
or stir stick
- Two eggs
In a tall clear glass with 8oz. of fresh (tap) water, mix in 7 tsp.
of salt and stir so it is dissolved. Then, in a separate small container,
mix a few drops of food coloring in a few ounces of fresh water, and
stir until well mixed. Now, take an eye dropper full of the colored
fresh water, and gently drop it on top of the salt water in the glass.
Watch how the colored fresh water floats on top of the salt water. Why
do you think this happens? For a clue, try this next experiment.
What do you think will happen when one egg is placed in salt water
and another in fresh water? Before performing this experiment--make
a prediction. What will happen to an egg placed in saltwater? In freshwater?
Using two tall clear glasses, fill one glass with 8oz. of fresh (tap)
water, and mix in 7 tsp. of salt and stir so it is dissolved; fill the
second glass with 8 ounces of fresh water. Carefully place one egg in
the glass with salt water, and a second egg in the glass with fresh
water. Do the eggs float or sink? Why? From what you see, what can you
tell about the difference between salt and fresh water? Ask yourself
if you seem to float more easily when you swim in the ocean or in a
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