Can you imagine the world without clocks? It was 400 years ago that Galileo got his idea for the first pendulum clock by watching the lamp in the dome of the cathedral swing back and forth with an even rhythm. The task in this chapter is for students to put themselves in Galileo’s shoes and make a pendulum timer from a weight tied to a length of string to determine how long the string needs to be for the weight to swing back and forth in one second. We don’t know how Galileo solved this problem, but science has come a long way since Galileo’s day. Scientists today would probably take a few more readings and then graph the data. Graphs help picture what is happening.