Physics
Galileo e Viviani, by Tito Lessi, 1892
Dome of the Cathedral of Pisa with the "lamp of Galileo"
Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the classical mechanics developed by Sir Isaac Newton.
Pendulum
Main article: Pendulum § History
Galileo conducted several experiments with pendulums. It is popularly believed (thanks to the biography by Vincenzo Viviani) that these began by watching the swings of the bronze chandelier in the Cathedral of Pisa, using his pulse as a timer. The first recorded interest in pendulums made by Galileo was in his posthumously published notes titled On Motion,[189] but later experiments are described in his Two New Sciences. Galileo claimed that a simple pendulum is isochronous, i.e. that its swings always take the same amount of time, independently of the amplitude. In fact, this is only approximately true,[190] as was discovered by Christiaan Huygens. Galileo also found that the square of the period varies directly with the length of the pendulum.
Sound frequency
Galileo is lesser known for, yet still credited with, being one of the first to understand sound frequency. By scraping a chisel at different speeds, he linked the pitch of the sound produced to the spacing of the chisel's skips, a measure of frequency.