The Eggs-Speriment
Saltwater versus Freshwater
The oceans have always been salty,
although most lakes and ponds are not salty.
Problem:
Do things float the
same way in a lake or on the ocean?
Grade:
Time:
Topic:
Concept:
SOL:
Science:
Rationale:
Goals:
Objective:
Materials:
two fresh raw eggs
two drinking glasses
tap water
table salt
a small scale
Procedure
- Fill one glass with tap water.
- Fill the other glass with the exact same amount of
tap water and add five heaping tablespoons of salt. Mix well.
- Carefully crack open an egg and gently set it on the
surface of the tap water. What happens to the egg?
- Now set the other egg on the salty water. Does the
egg do the same thing?
- Weigh the two glasses, and compare them. Which
weighs more? If you suspect that your eggs don’t weigh the same, try it
again and weigh the water-filled glasses ahead of time.
What's
happening?
The egg sinks in freshwater, but floats in salt water.
If you have the same amount of each, salt water weighs more than fresh water.
There is more “stuff” in salt water than in the same amount of fresh water.
We say salt water is denser than fresh water. The denser salt water can hold up
the weight of an egg. But the fresh water doesn’t have enough “stuff” in
it to support the same weight. Things float better in salt water than in fresh
water because salt makes water heavier.
Questions and Answers:
Question: Do the eggs behave the same way in the
tap water and in the salty water? Why or why not?
- Answer: The egg floats better in the salt
water than in the freshwater. This is because salt water is more dense and
thus weighs more, thus able to match the weight of the egg that displaces
the water.
Question: What would happen if you cracked open an
egg into the ocean? Why?
- Answer: It would float well. The ocean is
salty, thus is dense.
Question: What would happen if you cracked open an
egg into a fresh-water lake? Why?
- Answer: It would sink. Fresh-water lakes have
no salt, thus is not dense.
|
