Cause of motion by Descartes. Law of conservation. Inertial motion recognized. But still no clue to nature of impetus and momentum.

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RENE DESCARTES
CM [006] The Laws of

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René Descartes
René Descartes (1596–1650) was a French
philosopher and mathematician who
developed a theory known as the
mechanical philosophy. This philosophy was
highly influential until superseded by
Newton's methodology.
Carte’s achievement has be so well received
in his time that he has been dubbed the
father of modern philosophy, and much
subsequent Western philosophy is a
response to his writings,[which are studied
closely even to this day. In particular, his
Meditations on First Philosophy continues to
be a standard text at most university
philosophy departments. Wikipedia

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Definition of Motion
In the study of mechanics, Descartes
provided the first distinctly modern
formulation of laws of nature and a
conservation principle of motion.
He accepted the existence of inertial
motion (uniform or non-accelerating
motion) or bodily rest as natural
bodily states.
He regarded motion as “the action
by which some body is transferred
from one place to another”.

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Size and Velocity
The quantity of motion of a body is the size of the body times its speed. This is
not to be identified with momentum (mass x velocity), because for Descartes, size
and mass are not distinct concepts; at the same time, for Descartes, speed (scalar)
and velocity (vector) are not distinct concepts.

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Conservation of Motion
Descartes also envisioned the conservation of
quantity of motion as one of the fundamental
governing principles of the entire cosmos. When
God created the universe, he reasoned, a certain
finite amount of motion (quantity of motion) was
conferred to its material occupants; a quantity,
moreover, that God continuously preserves at each
succeeding moment. Part 2, Article 36.
Due to the immutability and constancy of God, the
total quantity of motion of bodies in the universe is
conserved.

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Conservation of Transference
It is obvious that when God first created
the world, He not only moved its parts
in various ways, but also simultaneously
caused some of the parts to push others
and to transfer their motion to these
others. So in now maintaining the world
by the same action and with the same
laws with which He created it, He
conserves motion; not always contained
in the same parts of matter, but
transferred from some parts to others
depending on the ways in which they
come in contact.
As to the cause of motion,
Descartes believed that God
is the primary cause, the rest
are secondary causes.
He said: Part II, Article 62.

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Summary of Descartes’s Law of Motion
According to Descartes, motion is governed by the following laws:
1. Each and every thing, as far as it can, always continues in its same state – in
motion or at rest.
2. This natural tendency to preserve the present state can be affected by
“external causes”.
The second law holds that “all movement is, of itself, along straight lines” (Pr II 39)
It also deals with circular motion and is not in our discussion here.
This law is as close to Newtons laws as any pre-Newtonian philosopher can get.
The renowned historian of science Clifford Truesdell (1919-2000) had observed,
“[Descartes' physics] is the beginning of theory in the modern sense”

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Nature of Impetus
As to the nature of
motion and the
transferred substance,
Descartes declared that
motion and rest are
primitive states of
material bodies. It does
not need of further
explanation. So from
Descartes, we still do not
get any clue as to what
impetus or momentum is.
?

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GALILEO’S INERTIA
To be continue on CM [007]
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