This Week's Experiment - #253 Light as Air
As usual for the holiday season, I am rereading Michael Faraday's Chemical
History of a Candle. I have also been reading a wonderful, antique science
book which my sister Sharla gave me for Christmas. Both books have versions
of this experiment, and I thought it would be a fun one. I will warn you
that it does require some math. (OK, calm down. Take a deep breath. Try to
relax. It won't hurt a bit.) Math is an important part of science and as
you will see, this is very simple math. You will need:
a measuring tape or a ruler
a room
This week we are going to investigate the weight of air. You probably have
heard someone say that something is as light as air. As we are going to see,
air is not as light as you might think. We will start with a one foot cube
of air. If you weighed it (Can you think of a way that you could?), that one
foot cube would weigh about 1.2 ounces or about 0.075 pounds. (If you want
to work in metric, one cubic meter of air weighs about 1.275 kilograms.)
That is the weight of air at sea level. It can vary depending on the
altitude, temperature and humidity. As it gets warmer or you are higher than
sea level, or the humidity is high, then the air will weigh a bit less. If
it gets colder, drier or you are lower than sea level, then the air will
weigh a bit more. (Yes, you can get lower than sea level and still be on dry
land. Check your geography book.)
Now 1.2 ounces probably sounds pretty light. To make it more impressive, we
need to find out how many cubic feet of air are in your room. This is
easier than it sounds. First, measure how wide your room is, from side to
side. If you want the math to be easy, you can round off the number to the
nearest foot. Write that number down and label it "width". Then measure how
long your room is. Write that number and label it "length". Finally,
measure how tall your room is. You may need some help for this one. Write
that number and label it "height".
Now we will multiply width times length. Then multiply that number by
height. That will give you the total number of cubic feet in the room. For
example, if your room is 10 feet wide, 12 feet long and 8 feet high, you
would multiply 10 X 12 to get 120. Then multiply 120 X 8 to get 960. That
tells us that the room could hold 960 cubic feet of air. Multiply that
number by 0.075 to find how many pounds of air your room holds. In this
case, it would hold 72 pounds of air!
If you want to try this at school, there is an easy way to measure a large
room without disturbing everyone with tape measures. Most school cafeterias
have tile floors. If you measure one tile, then you can count how many tiles
wide and how many tiles long the room is. If the walls are brick, you can
measure one brick and then count how many bricks tall the room is. Once you
get the width, length and height, it is easy. Measuring a large room, such
as a school cafeteria can truly surprise you with the weight of the air
inside.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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