Galileo Times Falling Bodies and Founds the Experimental Method
A ball, a grooved plank, and a water clock reveal the exact law hiding inside free fall
Quick facts
- Published
- 1638, Discourses and Mathematical Demonstrations Relating to Two New Sciences
- Law of falling bodies
- Distance from rest proportional to the square of elapsed time
- Timing method
- Water clock, weighed water jet
- Reported trials
- "a full hundred times"
What happened
Unable to time free fall directly with the clocks of his day, Galileo Galilei slowed the motion down by rolling a bronze ball along a grooved, inclined wooden plank and measuring elapsed time with a water clock, a vessel that released a thin jet of water he could weigh at each interval. In his own account, reproduced by the University of Virginia's physics history archive, he ran the trial a full hundred times and always found that the spaces traversed were to each other as the squares of the times. This confirmed his law that a uniformly accelerating body picks up equal amounts of speed in equal time intervals, and that distance from rest grows with the square of elapsed time. Galileo published the result in 1638 in Discourses and Mathematical Demonstrations Relating to Two New Sciences, his final book, written after Church authorities had already placed him under house arrest for his defense of a Sun-centered cosmos.
Why it matters
Galileo's inclined-plane experiments replaced Aristotle's claim that heavier bodies fall faster with a precise, testable mathematical law, and just as important, they replaced pure argument with repeated, measured experiment as the way to settle a physical question. The MacTutor archive credits his 1590s work De Motu with the idea that theories can be tested by experiment; Two New Sciences in 1638 is where that method produced a durable, quantitative law of nature.
How we know
Galileo's own descriptions of the inclined-plane and water-clock apparatus, including the number of trials and his stated timing precision, survive in Two New Sciences and are reproduced and analyzed by university physics-history archives such as the University of Virginia's Galileo and Einstein project.
Sources
- MacTutor History of Mathematics, University of St Andrews. Galileo (1564 - 1642) · Primary source (author-declared)mathshistory.st-andrews.ac.uk · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- Galileo and Einstein, University of Virginia Department of Physics. Galileo's Acceleration Experiment · Primary source (author-declared)galileoandeinstein.phys.virginia.edu · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- The Scientific Revolution → · Galileo's kinematics and experimental method were a central pillar of the wider Scientific Revolution; see that timeline for the astronomy, anatomy, and philosophy unfolding alongside it.