Numismatics is a field which is totally devoted to the study of all manifestations of money. This obviously includes the study of notes and coins that have been used as representations of money since ages. Coin collection is a favorite pastime for many, who tend to be interested in collecting rare things. Metal coins have been in use since ancient times, and even today paper money hasn't entirely replaced them. An expert numismatist, with a particular interest in coins, will have a complete profile of every coin that he or she has collected, which includes its physical characteristics like weight and dimensions, as well as the history of the coin's minting and its usage. One of the coins with a rich history of usage is the penny. US, Canada, and UK use it as a part of their national coinage.
The word 'Penny' has its origins in the old English name for it, which was penning or penig. These words themselves can be traced back to the English word for a token or pledge, which is 'pawn'. In many English-speaking countries, it is the lowest denomination of money. In USA, a penny is exactly one hundredth of a dollar in monetary value. Officially, in USA, it is actually known as a 'cent'.
Symbolized as '¢', the penny has been in circulation in USA now, since 1793. Since then, this coin has undergone changes in the kind of materials used for its manufacturing and the representations imprinted on it. Since 1909, the obverse has been imprinted with the profile of President Abraham Lincoln. Till date, several new versions of the coin have been introduced to commemorate the birth anniversary of President Lincoln.
At present, the US penny, minted by the treasury, weighs 2.5 gm, has a diameter of 1.905 cm (0.75 in), with 0.155 cm thickness, and a plain edge. A 2010 penny weighs 2.5 gm. Since 1983, it's composition material has been copper plated zinc. Since 2010, the newly minted pennies, feature the Lincoln union shield. Interestingly, the cost of minting them in 2010 was greater than their actual value.
Reports indicate that the cost of minting a US penny is USD 0.0179, which is greater than its inherent value, which is USD 0.01. In pounds, it roughly weighs 0.0055 lb. In ounces, it roughly weighs 0.0882 ounce.
Neighboring Canada too, owing to its English heritage, has a penny, as part of its monetary system. Even in Canada, its value is 1/100th of a dollar. It has been in circulation since 1858. A Canadian penny weighs 2.35 gm, has a diameter of 1.905 cm, has a thickness of 0.145 cm, and comes with a smooth edge. So, it is lighter than its US counterpart. It has an inscription of Queen Elizabeth II on the obverse side and a maple leaf, with its monetary value imprinted on the reverse side.
In UK, the 'Penny Sterling' is exactly 1/100 of a Pound Sterling, which is the UK currency. An English penny weighs 3.56 g and has a diameter of 2.032 cm. It comes in two versions - a steel and a bronze one and both have the same weight, though their thickness varies. So the weight of this coin in UK is substantially more than its counterparts in US and UK.
Indeed, evolution of the concept of money and the way coins of different eras represent the changing sociopolitical and economic circumstances, are interesting subjects of study. You can explore the rich history of minting pennies and their usage, even further.