Galileo Galilei (1564-1642) | A Particle in Motion...Galileo's Life | The Parabolic Path...A Modern View The Parabolic Path...Galileo's View | References | Back to the front page The Parabolic Path...Galileo's View
Vincent W. Lau
The modern view of projectile motion requires one to study modern concepts such as velocity and acceleration. The irony is that Galileo himself is responsible for these ``modern'' concepts. So by studying how we explain projectile motion today, we are really studying Galileo's explanation as well. What is of interest, though, is how Galileo came to the conclusions that we study today.
Galileo exposed the world to his physical findings in a book entitled
In Sagredo: ...a fine thing if you were able to give some quick and easy rule by which a mechanician might draw a parabola upon a plane surface? What is interesting is the conclusion that Galileo draws from his simple, yet effective, method of drawing parabolas above:
Salviati: ...[the] experiment furnished clear and tangible evidence that the path of a projectile is a parabola.
In the Fourth Day (chapter) of
Imagine any particle projected along a horizontal plane without friction; then we know...that this particle will move along this same plane with a motion that is uniform and perpetual [constant velocity with no acceleration], provided the plane has no limits. But if the plane is limited and elevated, then the moving particle...will on passing over the edge of the plane acquire, in addition to its previous uniform and perpetual motion, a downward propensity due to its own weight [gravity]; so that the resulting motion which I call projection, is compounded of one which is uniform and horizontal and of another which is vertical and naturally accelerated [which is the same as our results in Eqns. (6), (7), (8) and (9)]. The statement above is just a wordy version of the equations obtained in the previous section. Galileo puts it all together and what results is the theorem we have spent our time discussing:
It is amazing that Galileo, through experiment, found this result that we still use and teach today. We are fortunate to have been allowed to reap the rewards of his genius, and although Galileo is best known for his work in astronomy, we must be grateful that he chose to lead us onto the right path in physics.
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