Newton's cannonball was a

thought experiment A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most anc ...

Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the grea ...

used to hypothesize that the force of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

was universal, and it was the key force for planetary motion. It appeared in his posthumously published 1728 work ''De mundi systemate'' (also published in English as '' A Treatise of the System of the World'').''De mundi systemate''
Isaac Newton, London: J. Tonson, J. Osborn, & T. Longman, 1728.''A Treatise of the System of the World''
Isaac Newton, London: printed for F. Fayram, 1728.

Source of the experiment

Newton's original plan for '' Philosophiæ Naturalis Principia Mathematica'' was that it should consist of two books, the first analyzing basic laws of motion, and the second applying them to the Solar System. In order to include more material on motion in resisting media, the first book was split into two; the succeeding (now third) book, originally written in a more popular style, was rewritten to be more mathematical.''A Treatise of the System of the World''
Isaac Newton, introd. I. Bernard Cohen, Dover Phoenix Editions, 2004, . However, manuscripts of an earlier draft of this last book survived, and a version of it was published in 1728 as ''De mundi systemate''; an English translation was also published earlier in 1728 under the name ''A Treatise of the System of the World''. The thought experiment occurs near the start of this work.

Thought experiment

In this experiment from his book (pp. 5–8), Newton visualizes a stone (you could also use a cannonball) being projected on top of a very high mountain. If there were no forces of gravitation or air resistance, the body should follow a straight line away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, in the direction that it was projected. If a gravitational force acts on the projectile, it will follow a different path depending on its initial velocity. If the speed is low, it will simply fall back on Earth. (A and B) for example horizontal speed of 0 to 7,000 m/s for Earth. Newtonsmountainv=0

If the speed is the

orbital speed In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if one body is much more mas ...

at that altitude, it will go on circling around the Earth along a fixed circular orbit, just like the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. (C) for example horizontal speed of at approximately 7,300 m/s for Earth. Newtonsmountainv=7300

If the speed is higher than the orbital velocity, but not high enough to leave Earth altogether (lower than the

escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...

), it will continue revolving around Earth along an elliptical orbit. (D) for example horizontal speed of 7,300 to approximately 10,000 m/s for Earth. Newtonsmountainv=8000

If the speed is very high, it will leave Earth in a parabolic (at exactly escape velocity) or hyperbolic trajectory. (E) for example horizontal speed of approximately greater than 10,000 m/s for Earth. Newtonsmountainv=10000

Other appearances

An image of the page from ''A Treatise of the System of the World'' showing Newton's diagram of this experiment was included on the

Voyager Golden Record The Voyager Golden Records are two phonograph records that were included aboard both Voyager spacecraft launched in 1977. The records contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for ...

Sagan, Carl ''et al.'' (1978) ''Murmurs of Earth: The Voyager Interstellar Record''. New York: Random House. (hardcover), (paperback) (image #111). Voyager_golden_record_111_systemoftheworld

Voyager_golden_record_111_systemoftheworld

Notes

External links

Newton Thought Experiment Simulator
*[https://books.google.com/books?id=DXE9AAAAcAAJ&ots=e9UwdajVlO&dq=A%20Treatise%20of%20the%20System%20of%20the%20World&pg=PA6-IA1#v=onepage&q=&f=false Drawing in the 1731 (2nd) edition of 'A Treatise of the System of the World' @ Google books]
Newton's Cannon animation
{{DEFAULTSORT:Newton's Cannonball Isaac Newton Thought experiments in physics Space guns

Source of the experiment

Thought experiment

Other appearances

See also

Notes

External links