Buoyancy of an Egg in Water
Purpose:
You'll learn about density, diffusion and buoyancy.
On their trip to the North Magnetic Pole, explorers will encounter
salt and fresh water, and ice formed from these two liquids. Density,
diffusion and buoyancy are important to helping the explorers understand
how the salt water ice becomes fresh water ice that can be melted for drinking
water.
Definition of terms:
Density - the weight of something in relationship to its volume.
Diffusion - to spread out
Buoyancy - ability to float
What you will need:
1 tall glass
common table salt
cold water
1 large egg
Before you begin:
Ask an adult to help you with this activity.
What to do:
-
Place the tall glass on a level table.
-
Pour the salt into the glass so that there is a bed of salt 2 to 3 inches
thick on the bottom of the glass.
-
Tilt the glass to one side and gently pour cold water down the side of
the glass onto the bed of salt until the glass is 3/4 full.
-
Gently drop the egg into the water. It will come to rest on the bed
of salt.
-
Watch for the next few days to see what happens.
What is going on here?
As time passes, the salt slowly dissolves into the water. The
salt particles, or ions, diffuse upward above the bed of salt. As
the salt dissolves and diffuses upward, the density of the water increases.
The density increases because the salt particles are small enough to get
in between the water molecules and occupy space that was not previously
occupied.
When you first drop the egg into the water, the egg's density is greater
than the water's density. Therefore, the egg sinks to the bottom.
As the density of the solution increases, the egg becomes buoyant and rises
in the glass.
Activity courtesy of Jeff Ward, a member of the Arctic Exploration Team.
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