Defining Density
A colorful way to teach your children the concept of differing
densities
What weighs more: A ton of ping-pong
balls or a ton of steel? Actually, they both have the same mass.
Many who are fooled by this question are grappling with density as
opposed to mass. When considering density, it is important to
consider the mass of an object as well as the volume or size of
the object. For example, if two identical containers were filled,
one with sand and one with water, which one would have the
greatest mass? To answer this question, you would have to consider
the density of each substance filling the containers. Here’s a fun
and interactive science experiment to teach your children about
differing densities.
Materials
Procedure:
Step 1:
One at a time, carefully pour the
molasses, water and cooking oil into the bottle. Pour the liquids
over the back of a spoon so that they do not mix. It’s best to do
this in the kitchen sink to make any clean up a breeze.
Step 2:
Observe. As things settle down, the
liquids will separate into three different layers. The molasses
sinks below the water, while the oil floats to the top.
Step 3:
Try floating different objects, such
as a cork, a slice of apple, a paper clip, a grape or any other
object that you can find. Do they float? What layer do they float
on?
During step three take a moment to explain density to your
children. In short, density is the measure that describes the
degree of compactness of a substance. Another way of looking at it
is how heavy is something for its size. A truckload of ping-pong
balls will have less mass than an equal sized load of truckload of
steel bars.
A common example of differing densities can be found in your
refrigerator. Take a look at a bottle of salad dressing and you
will see that the oil and vinegar do not mix as they have
different densities.
This experiment, like the bottle of salad dressing, shows that
different liquids have different densities, meaning some liquids
are heavier than others and will tend to sink to the bottom, while
others float to the top. Different objects will float on different
layers of liquid depending on their density.
The density of water is one gram per cubic centimeter, so density
is easily understood in terms relative to water. Because the
cooking oil floats on water, its density is less than one.
Therefore, the density of molasses must be greater than one
because sinks below the water.
Try replacing the molasses with honey, or the water with milk.
What happens? And for more fun, add different food colors to
different liquids and create a density rainbow.
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children by providing them with fun, entertaining and educational
activities that instill a clear understanding of what science is
really about and how it affects the world around them . For more
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