This week’s question was asked by a friend.
QUESTION: What is a Fermi question?
ANSWER: Here are some Fermi questions: Car tires wear down, so how many atoms are lost in each rotation of a car tire on the road? How many hairs are there on a human head? What is the volume of human blood in the world? How many drops of water are there in Lake Erie? How large a collision is needed to split the moon in half? How much electrical power does the United States use per year? How many piano tuners are in New York City?
A Fermi question requires an estimation of physical quantities to arrive at an answer that is at least within a power of 10 − in other words, 10 times too little or 10 times too much. The goal of a Fermi question is to get an answer by making reasonable assumptions about the situation, not necessarily coming up with an exact answer.
Fermi questions is one of the events in Science Olympiads held in high schools across America and in many foreign countries. The process requires students to ask many more questions to arrive at a best estimate. The team must rely on open communication between its members, estimation abilities and math skills. A Fermi question emphasizes process rather than “the answer,” because some answers are almost impossible to come by.
Take, for example, the question “How many drops of water are there in Lake Erie?” requires an estimate of the volume of a drop of water, the volume of Lake Erie from its approximate dimensions and conversion of units to yield an answer.
Enrico Fermi (1901-1954) is one of my favorite scientists. He combined a probing, questioning mind with intense personal drive. He was always looking for a new challenge, be it skiing, mountain climbing, or swimming. Fermi has been called the last of the double-threat scientists. He combined a brain that conceived wonderful, elegant theories to explain nature with a pair of hands that built and operated impressive laboratory experiments.
Fermi was an Italian physicist best known for his contributions to nuclear physics and the development of quantum theory. He is also noted as an experimentalist. Fermi earned the Nobel Prize for his physics work on the nuclear process and was awarded several patents on the use of nuclear power.
Shortly after receiving the Nobel Prize in 1938, Fermi was forced to flee Mussolini’s Italy. His wife, Laura, was Jewish. He and his family settled in the United States, first at Columbia University and then later at the University of Chicago.
Fermi led the team that designed and built the crude nuclear reactor that obtained the first artificial self-sustaining nuclear chain reaction on Dec. 2, 1942. During World War II he was a member of the Manhattan project team that developed the atomic bomb at Los Alamos, New Mexico.
In the early morning hours of July 16, 1945, the atomic scientists gathered at Trinity site, in the desert near Alamogordo, New Mexico. They huddled behind bunkers five miles from the windmill-like platform atop which sat the world’s first atomic bomb. To safely view the blinding explosion, scientists were issued welders glasses. Seconds after the blinding flash, a pressure shock wave swept by the observers.
Enrico Fermi grabbed a handful of sand and tossed it in the air as the shockwave passed by. Based on the distance the sand was swept downwind, Fermi estimated the yield of the first atomic bomb to be about 20,000 tons of TNT. Fermi’s reputation is cemented.
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Larry Scheckel is a retired Tomah High School physics teacher.