page_title: History of experiments
section_title: Galileo Galilei
hierarchical_section_title: History of experiments / Galileo Galilei
caption_attribution_description: English: The figure shows experimental data for the acoustically measured fall time of a small steel sphere falling from various heights. The data is in good agreement with the predicted fall time of sqrt(2h/g), where h is the height and g is the acceleration of gravity. (Data courtesy of E.R. Courtney.)
context_page_description: The history of experimental research is long and varied. Indeed, the definition of an experiment itself has changed in responses to changing norms and practices within particular fields of study.
context_section_description: Galileo Galilei as a scientist performed quantitative experiments addressing many topics. Using several different methods, Galileo was able to accurately measure time. Previously, most scientists had used distance to describe falling bodies, applying geometry, which had been used and trusted since Euclid. Galileo himself used geometrical methods to express his results. Galileo's successes were aided by the development of a new mathematics as well as cleverly designed experiments and equipment. At that time, another kind of mathematics was being developed—algebra. Algebra allowed arithmetical calculations to become as sophisticated as geometric ones. Algebra also allowed the discoveries of scientists such as Galileo—as well as later scientists such as Isaac Newton, James Clerk Maxwell and Albert Einstein—to be summarized by mathematical equations. These equations described physical relationships in a precise, self-consistent manner.
  One prominent example is the "ball and ramp experiment." In this experiment Galileo used an inclined plane and several steel balls of different weights. With this design, Galileo was able to slow down the falling motion and record, with reasonable accuracy, the times at which a steel ball passed certain markings on a beam.  Galileo disproved Aristotle's assertion that weight affects the speed of an object's fall. According to Aristotle's Theory of Falling Bodies, the heavier steel ball would reach the ground before the lighter steel ball. Galileo's hypothesis was that the two balls would reach the ground at the same time.
  Other than Galileo, not many people of his day were able to accurately measure short time periods, such as the fall time of an object. Galileo accurately measured these short periods of time by creating a pulsilogon. This was a machine created to measure time using a pendulum. The pendulum was synchronized to the human pulse. He used this to measure the time at which the weighted balls passed marks that he had made on the inclined plane. His measurements found that balls of different weights reached the bottom of the inclined plane at the same time and that the distance traveled was proportional to the square of the elapsed time. Later scientists summarized Galileo's results as The Equation of Falling Bodies.
  These results supported Galileo's hypothesis that objects of different weights, when measured at the same point in their fall, are falling at the same speed because they experience the same gravitational acceleration.
caption: Measured fall time of a small steel sphere falling from various heights. The data is in good agreement with the predicted fall time of 
    
      
        
          
            
              2
              h
              
                /
              
              g
            
          
        
      
      {\displaystyle {\sqrt {2h/g}}}
    
  , where h is the height and g is the acceleration of gravity.
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