CM [004] Buridan's Impetus

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JEAN BURIDANCM [004] The Renegade Monk


Jean Buridan

Jean Buridan (1295-1358) was a French priest credited to be the person who sowed the seeds for the Copernican revolutionin Europe.

Before Buridan, natural philosophy was only a handmaiden of theology or a mere disciple after the doctrines of Aristotle. After the time of Buridan, it began to have its own legitimacy and developed in a new direction.


Motion of Projectiles

Like Philoponus in the 6th century, Buridan was particularly in discordance with Aristotle’s concept on motion of projectiles.

The trajectory of a projectile by Aristotle


Buridan on Projectiles

Buridan said: “. . . after leaving the arm of the thrower, the projectile would be moving by an ‘impetus’ given to it by the thrower and would continue to move as long as the impetus remained stronger than the resistance, and would be of infinite duration were it not diminished and corrupted by a contrary force resisting it or by something inclining it to a contrary motion.”

IMPETUS


Buridan’s Impetus

According to Buridan in his “Quaestiones on Aristotle's Physics”:

“When a mover sets a body in motion he implants into it a certain impetus:

[𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼]

. . . a certain force enabling a body to move in the direction in which the mover starts it, be it upwards, downwards, sidewards, or in a circle.

[𝐷𝐷𝑀𝑀𝐷𝐷𝐼𝐼𝐷𝐷𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝐼𝐼𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 =𝐷𝐷𝑀𝑀𝐷𝐷𝐼𝐼𝐷𝐷𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝑀𝑀𝐼𝐼𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼]


Buridan’s Equation

The implanted impetus increases in the same ratio as the velocity.

[𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼 ∝ 𝑉𝑉𝐼𝐼𝑉𝑉𝑀𝑀𝐷𝐷𝑀𝑀𝑀𝑀𝑉𝑉]

in fact, Buridan gave it a mathematical formulation:

𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼 = 𝑊𝑊𝐼𝐼𝑀𝑀𝑊𝑊𝑊𝑀𝑀 × 𝑉𝑉𝐼𝐼𝑉𝑉𝑀𝑀𝐷𝐷𝑀𝑀𝑀𝑀𝑉𝑉

The weight is a constant that does not change. So the impetus is purely a function of velocity.

Faster object has greater impetus


INERTIA

Impetus became Momentum

It can be said that what Buridan did was very close to defining momentum in the Newtonian sense 𝒑𝒑 = 𝐼𝐼𝒗𝒗.This impetus theory was revived in the thirteenth century by Peter John Olivi (c.1248-1298) and has been incorporated into modern physics as momentum.

Buridan’s IMPETUS


Nature of Impetus

Apparently Buridan’s way of thinking was on the right track. But again like Philoponus, he did not investigate further why it should be as he thought. It seemed to him that it was an elementary fact and resumed no further explanation. What is impetus? What is in impetus that is passed on from one body to another to make a body move?

IMPETUS

?


FRICTIONTo be continued on: CM [005] The Discovery of

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CM [004] Buridan's Impetus