Showing posts with label Physics. Show all posts
Showing posts with label Physics. Show all posts

Monday, April 1, 2019

Albert of Saxony & Impetus

After the previous post on impetus, I wanted to introduce you to Albert of Saxony, who took Avicenna's idea a step further.

Albert of Saxony (c.1320 - 8 July 1390) was the son of a German farmer who became a bishop of Halberstadt after studying at the University of Prague, the University of Paris, and the Sorbonne. He went to Pope Urban V as an envoy of Austria to negotiate the founding of the University of Vienna, whose rector he became in 1353.

A pupil of Jean Buridan in his youth, he was influenced by Buridan's teachings on logic and physics. He worked out his own theory of impetus, based on his predecessors and adding the third or "final" stage of a moving object. Prior to this, it was accepted that
1. the initial force causes the object to move in a straight line (A-B)
2. the object deviates from its path as impetus fades (B)

To this theory, Albert added the third stage:
3. the impetus or force which causes the initial movement is spent, and gravity draws the object downward vertically (C), where it stops (D).

Modern physics would describe this progression as an example of inertia. It seems obvious to us, but these ideas and their descriptions had to start somewhere!

The careful, methodical way in which he laid out his thoughts, and his commentaries on Aristotle's Physics, made him more widely read in the Middle Ages than Buridan. The widespread distribution of his works spread the ideas of the University of Paris throughout Italy and central Europe.

Friday, March 29, 2019

The Theory of Impetus

1582 woodcut demonstrating
impetus with artillery
Impetus is the force or energy with which a body started to move. The term itself entered the English language in the 17th century, but the concept was studied long before that.

Aristotle thought that, for an object in motion to continue to move, it must have a continuous force behind it. John Philoponus in the 6th century thought rather that the initial force was necessary and did not need anything else, but that the initial force would therefore be only temporary; hence an object in motion's observed tendency to slow and stop. Avicenna in the 11th century agreed with him, calling the phenomenon "projectile motion."

In the 12th century, an Islamic philosopher, Hibat Allah Abu'l-Barakat al-Baghdaadi, recognized (finally!) that the motive force diminishes with distance from the mover.

Jean Buridan, writing in French in the 14th century, called this force "impetus" (from Latin impetere, "to assail"), and even expressed it mathematically: impetus = weight x velocity. Even he, however, treated impetus as if it were momentum. Modern physics distinguishes the two thusly: impetus is the initial force behind a moving object, momentum is "the quantity of motion of a moving body." It seems universally understood by anyone who has ever thrown a ball that Aristotle's option of a continuous motivating force is simply quaint.

Buridan understood that there was resistance (such as the air) that caused the impetus to fade. There was a case, however, in which impetus did not have resistance. God, when putting the celestial spheres in motion, did so in a way that created infinite impetus so that they would (obviously!) never stop moving.

To which the medieval world replied: Thank Heavens.

Monday, May 21, 2012

The Oxford Calculators

The men before Galileo

In the first half of the 1300s, a handful of scholars at Oxford University, most of whom were at Merton College, applied observation and careful thought to what had been proposed by Aristotle and other Classical philosophers.

Their first innovation was to distinguish between kinematics (motion of bodies regardless of the forces acting upon them) and dynamics (the study of the forces that initiate or affect motion). Their use of observation, experimentation, and mathematics led them to understand that Aristotle was wrong when he said the motion/speed of a falling body was determined by its weight (which, to Aristotle, was affected by the proportions in the object of the four elements; water and earth tended to make it fall faster, while a greater amount of fire or air made it fall more slowly). They understood that two bodies of different weights accelerated similarly; they were able to prove this with math. This knowledge spread to universities on the continent. Nicholas Oresme, a bishop in France, and Giovanni di Casali, a Franciscan in Italy, were each inspired to produce graphs and diagrams to explain this motion.

Despite this dissemination of information, it is assumed that these works were not likely to have been known by Galileo (1564-1642), who gets the credit in physics texts for developing the theory of falling bodies.