Academic journal article Science and Children

# Fermi, for You

Academic journal article Science and Children

# Fermi, for You

## Article excerpt

Using a globe alone, get an estimate of the circumference (distance around) of the Earth. No fair looking up the answer, even if it's printed on the globe. Alternatively, take a look at the clear night sky where you live. Estimate how many stars are visible. Clearly you don't want to waste hours and hours counting them all, and the answer will depend on how close you are to the lights of civilization. Both of these tasks (called Fermi problems) are surprisingly easy, but not if you've never tried such a thing. Find out the answers next month, or now--in the digital edition of S&C. Not receiving the digital edition? Go to www.nsta. org/publications/digital journals.aspx.

The answer to last month's question:

Stand in front of a flat mirror. How far away from you is your image? As far behind the mirror as you are in front of the mirror. So, if you're 2 feet away from the mirror, your image is 2 feet behind the mirror, and thus 4 feet away from you. Staring for a while will convince you of this.

Now either put a flat mirror behind you or just imagine that you're doing it. Suppose the second mirror is 2 feet behind you. …

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