The discovery of radioactivity in the late 1800’s allowed scientists to develop new methods of determining the absolute age of rocks. Since it is not safe for us to play with radioactive isotopes, we will use pennies to simulate radioactive decay. The plastic box in this lab represents an imaginary rock.
Suppose that 100 heads-up pennies in your box represent atoms of an imaginary radioactive element called Headsium. When Headsium “decays”, it becomes a different imaginary element called Tailsium, which is stable (non-radioactive). After you shake the box for 15 seconds, approximately half of the pennies will have decayed (flipped over) to stable Tailsium. Thus 15 seconds is the half-life for Headsium.