If you flip a penny in the air, you can tell when it was made, roughly. If it was minted prior to 1982, it will give you a metallic ping during the course of its flip flight. After 1982, it will just give a very unsatisfying clarnk.
The rising price of copper finally took its toll on the Lincoln cent in 1982. The composition in 1982 was changed to an alloy of 99.2 percent zinc and 0.8 percent copper, plated by pure copper – making the total composition 97.5 percent zinc and 2.5 percent copper.
If you plan to use this knowledge in a bar bet, beware of the 1982 pennies. Some are of the old composition, some of the new. You are warned.
That concludes The Coolest Thing I Have Ever Seen.