A simple pendulum consists of a weight, called a bob, attached to a string which is fixed at the other end. The pendulum has been used since the 16th century to measure time. Galileo was the first to observe its properties.
Rather than focusing on students memorizing what does and does not affect the period of a pendulum, I chose to have students focus on the process of science. During this activity students were making predictions, using prior knowledge and devising tests.