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Packing Tightly: Density Experiments
by Anjali Amit
Which is heavier: a pound of cotton or a pound of lead? Cotton is soft and fluffy, and you can huff and puff and blow it all about. Lead is heavy, solid, and difficult to lift. Read the question again. It says "a pound of cotton or a pound of lead." The answer then is that they both weigh the same. But the question highlights density: Density tells us how much matter there is in a given volume. The more densely matter is packed in an object the heavier it will be. Here are some experiments to demonstrate density.
Experiment One:
What you need:
A container of water
A cork
A rock of the same approximate size and weight as the cork
What to do:
Lower both objects into the water.
What happens:
The cork floats.
The rock sinks.
Why:
The matter in the rock is packed more closely together than the matter in the cork.
The rock is denser than water, therefore it sinks.
Extension of the Experiment:
What you need:
Different objects of about the same size and weight
What to do:
Lower them in water.
Make a list of the objects that float and those that sink.
Why:
Objects that are less dense than water will float. The heavier objects will sink.
Experiment Two:
What you need:
A measuring cup or graduated cylinder
1/3-cup oil
1/3-cup water
1/3-cup corn syrup
What to do:
Pour the corn syrup into the cup or cylinder.
Tilt the container and slowly pour the oil down the side to prevent mixing.
Finally pour the water in a similar fashion.
What Happens:
The corn syrup settles on the bottom.
The water slides under the oil to make the second band.
The oil is on top.
Why:
The corn syrup is the densest of the three so it sinks to the bottom.
Oil is less dense than water. Although it is poured in second, it rises to the top.
The water slides below the oil. The liquids show as separate bands according
to their density.
Extension of the Experiment:
What you need:
A heavy nail
Pasta
A cork
What to do:
Carefully drop the objects into the measuring cup or graduated cylinder.
What happens:
The nail sinks to the bottom.
The pasta floats on the syrup.
The cork floats right on top the oil.
Why:
The nail is denser than all the liquids, so it sinks to the bottom.
The pasta is denser than the oil and water, but less dense than the syrup,
so it floats on the syrup.
The cork has the least density and floats right on top of the oil.
Conclusion:
Density demonstrates how tightly or loosely matter is packed in an object. Imagine having to pack a suitcase. The tighter you wedge the clothes, the more clothes you can fit in. The more clothes, the heavier the suitcase will be. Exactly the same holds true of all objects. A paper plate will be lighter than a ceramic plate, for example. Each element and compound has its unique, identifying density. Knowledge of the density of an object and how it behaves at different temperatures helps scientists construct safer ships, planes, and machines.
Bibliography
Farndon, John. Science Experiments Buoyancy. NY: Marshall Cavendish, 2003.
Mandell, Muriel. Simple Science Experiments with Everyday Materials. NY: Sterling Publishing Co., 1989.
Sullivan, Navin. Measure Up! Weight. NY: Marshall Cavendish Benchmark, 2007.
Interesting Web Sites:
http://www.elmhurst.edu/~chm/vchembook/120Adensity.html
http://www.nyu.edu/pages/mathmol/textbook/density.html
http://www.visionlearning.com/library/module_viewer.php?mid=37
Anjali is a children's book author whose first book,"Folk Tales From Rajasthan", was published when she was in college. Upon graduation she "sold her soul to Mammon"—went to work for a bank. She writes fiction, non-fiction, and edits technical documents. Her articles have appeared in various magazines. "Bedtime Stories from Around the World", her second book, was published a few years ago.
