Bearable Lightness

May 30, 2008 – 12:25 am

In past posts, I've talked about how heavy things are, but what about how light they are?

Over the Memorial Day Weekend, my mom and stepdad visited to celebrate her birthday, and as I was describing this little experiment in blogging to her, she suggested I use "light as a feather" as a theme. I thought that was a good idea and there were probably lots of sites online where I could find out the weight of a feather.

Wrong... for a number of reasons. Every bird has a number of different types of feathers of different sizes, textures, and weights. And then you have the fact that different sized birds of the same breeds will have different sized feathers, so the flight feathers from two eagles could weigh different amounts.

One thing I did run across, though was this answer to the question of how much a feather weighed. I liked his methodology, which was to estimate the weight of all the feathers on a bird and then get an average per-feather weight. Since Rough Equivalents are nothing if not inexact (they're roughly the right number, but we're not calculating to 100 places of pi), this sounded good. Unfortunately, his numbers were really bad guesstimates.

See, he'd read somewhere (as I did in my research) that a bird's feathers weighed about twice as much as the bird's skeleton. This is true of a bald eagle. But he guesstimated that on a 20 pound bird, you had 5 pounds of "guts," 5 pounds of skeleton, and 10 pounds of feathers. Estimating 8,000 feathers on his bird, he came up with a figure that a feather weighed .00125 pounds. That's 1/800th of a pound, or around .57 grams. But that's pretty heavy when you're going for things that are light. A small paper clip is only .5 grams.

I did more research and found a number of sites stating that, on a bald eagle, the skeleton represents 5-6% of the bird's weight, which would mean that the feathers would be 10-12% of its weight. If an average female bald eagle (the females are bigger than the males) weighed around 5.8 kilograms, 6% of that would be 348 grams. Double it and you've got 696 grams. Counts of the feathers on an eagle range between 7000 and 7200, so we'll split the difference at 7100.

So how much does a feather weigh? For a bald eagle, her feathers average out to roughly 98 milligrams each, or just under 1/10th of a gram. So when you get a headache and take two regular strength ibuprofen tablets, you're taking approximately 4 feathers of ibuprofen.

And now that I know the weight of a feather, I start thinking about the term "featherweight," which is a weight class in professional boxing. In the U.S. and England, a featherweight boxer weighs in at a maximum of 126 pounds or 583,191 feathers.

If you want to figure your weight in feathers...

• 10,201 feathers per kilogram
• 4628.5 feathers per pound
• 289.25 feathers per ounce

But another fun thing I ran across was the weight of air. If anything's lighter than a feather, air's got to be it. But air is heavier than you might think. At 1 atmosphere, or "sea level", one liter of air weighs roughly 1.2 grams, or one cubic meter of air weighs 1.2 kilograms.

An olympic size pool contains 2500 cubic meters of water. Replace that water with air and you've got 3,000 kilograms (3 metric tons) of air. So the air in an "empty" olympic size swimming pool weighs about the same as the curb weight of a Hummer H2.

Of course, my mother called while I was writing this, and I told her that fact, so she asked me how much an airhead weighs. Well, the average volume of a human skull is 1.4 liters, meaning 1.68 grams of air in an airhead... or 17 feathers.

What Rough Equivalents can you come up with for air and feathers? Post them in the comments below.