Science | Science Experiment of the Week 5 | 253 - Light as Air

Measure the weight of the air in your room - 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.

This Week's Experiment - #253 Light as Air

These experiments are from Robert Krampf - The Happy Scientist

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.

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