Density: Floating, Sinking, and Suspending

Ayodeji Griffin                Robert Fulton Elementary School
                               5300 South Hermitage Avenue
                               Chicago IL 60609
                               (312) 535-9000

Objective:

This mini-teach is designed for the primary and intermediate grade levels.
The students will observe the change in density by using a variety of different 
objects to make them float, sink, or suspend in various liquid solutions.

                                Raise the Raisins


Materials Needed:

Jar/Beaker
Clear Cabonated Drink (Sprite or 7Up)
Raisins

Strategy:

1.  Fill a jar/beaker full of clear carbonated drink.
2.  Add a handful of raisins to the jar.
3.  Observe the jar.

Performance Assessment:

The students will be asked why do the raisins keep rising and falling inside the 
jar/beaker. 

Conclusion:

This demonstration works because the bubbles of carbon dioxide gas in the drink
are much less dense than the drink or the raisins.  Once the raisins begin to 
move, they will keep rising and falling inside the jar for about an
hour.

When you drop the raisins into the jar/beaker of carbonated drink, the raisins 
are more dense than the drink, so the raisins sink.  When the raisins reach the 
bottom of the jar/beaker, the gas bubbles stick to the wrinkles on the raisins, 
thus causing the raisins to rise.  When the raisins reach the top of the 
jar/beaker, the gas bubbles burst.  Now the raisins are more dense than the 
carbonated drink, so the raisins will sink again.  When the raisins are covered 
with bubbles again, they are less dense than the carbonated drink, so the 
raisins will rise again.  This process will continue for about an hour. 


                                  Float the Egg

Materials Needed:

2 Jars/Beakers
Hard Boiled Egg
Salt
Tablespoon
Water
Pencil
Paper Towels
Food Coloring
Bowl/Container

Strategy:

1.  Fill one jar/beaker full of water.  (Do not fill it to the top.)
2.  Gently lower an egg into the jar/beaker of water.
3.  Observe the egg.
4.  Take the egg out of the jar/beaker.
5.  Pour ten (10) tablespoons of salt into the water and stir until it
    dissolves.  (This salt and water solution is called brine.)
6.  Gently lower the egg in the brine solution.
7.  Observe the egg.

Performance Assessment:

The students will be asked how can an egg float by changing the density of the 
water and not the egg.

Conclusions:

This demonstration will illustrate how an egg can float by changing the density
of the water, not the egg.  When the egg is lowered into the jar/beaker of
water, it will sink because it is more dense than the water.  After pouring the
ten (10) tablespoons of salt into the water, a solution is formed called brine.
When the egg is placed into the brine, the egg should float.  This is because
the salt has made the water more dense than the egg.

                                Suspend the Egg:

Once you demonstrate how an egg can float, you can amaze your students by 
suspending the egg in the middle of the jar/beaker.  For a "spooky" effect,
draw a face on the egg first.

Strategy:

1.  Place the egg in the brine solution and make a pencil mark on its highest
    point.  (You may have to hold the egg slightly in place when marking the
    egg.)
2.  Take the egg out of the brine solution and dry it.
3.  Draw a face on the egg, with the pencil mark between its eyebrows.

4.  Draw another face on the opposite side of the egg.
5.  Pour out the brine solution into another container or into the sink until
    the glass is half full.
6.  Mix a few drops of food coloring into a jar/beaker of cold water. 
7.  Tilt the glass that contains the brine solution gently, then slowly pour
    the cold colored water on top of the brine solution.
8.  When the glass is full, carefully slide in the egg.
9.  Observe the egg.

Performance Assessment:

The students will be asked why does the egg stay suspended in the jar/beaker.

Conclusions:

The reason why the egg stays suspended in the jar/beaker is because the water 
and the egg are less dense than the brine, so they float on top of it.  By
using the food coloring in this particular demonstration, you can also show how
water floats on brine.