The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Physics for Sciencetists and Engineers with Modern Physics. 5th Edition. Orland, Florida: Saunders College Publishing, 2000: 178.||"A penny of mass 3.10 g rests on a small 20.0 g block supported by a spinning disk."||3.10 g|
|Lincoln Cent. 1728 Software Systems. 2000.||"The number of pennies in the cup will have a mass of 100 grams. In case you are wondering, the number of pre-1982 pennies has a mass of 3.1 grams. (However, pennies made after 1982 is about 2.5 grams).||3.1 g
|Coin Specifications. U.S Mint.||"Composition: Copper Plated Zinc, 2.5 %Cu, Balance Zn, Weight 2.500 g, Diameter 0.750 in. 19.05 mm, Thickness 1.55 mm"||2.5 g|
|I weighed it myself.||
|3.1 – 3.2 g
The mass of a penny has changed throughout the years. The first Lincoln cent was produced in 1909 and had the wheat ears pattern on the reverse side. The composition of the penny was pure copper from 1793 to 1837. Then following that, it was made of bronze, and in 1857, it was made out of copper. In 1943, the content of the coin was changed to zinc coated steel because of the copper shortage during World War II. Before 1982, pennies were 95% copper and 5% zinc. Then after 1982, the compostion was 97.6% zinc, and 2.4% copper. So this means that the pennies made before 1982 will have a different mass from those made after 1982.
In a modern physics textbook, the mass of a penny was used as part of a word problem. It gave the mass of a penny to be 3.1 grams. Along with that information, I found a website that discussed the composition, mass, and density of a penny. The mass of a penny was 3.1 grams before 1982, but a penny after 1982 weighs 2.5 grams. According to the mint, from the United States Treasury website, to find out the mass of a penny, it also gave the mass as 2.5 grams.
So I decided to go out on my own and measure different pennies from different years. When I measured the 1980 and 1971 penny, it weighed 3.1 grams. The 1961 and 1956 pennies weighed 3.2 grams. But when I weighed the 2001 penny, it weighed 2.5 grams, which should be correct because it was made after 1982. So I basically found the same mass of a penny from all different sources.
Millicent Okereke -- 2002
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