The First Law of Motion

36. There are 2 causes of motion:

1. A universal and primary cause that is the general cause of all motions in the world

2. A particular cause, by which individual parts of matter acquire motions they did not have before.

The universal and primary cause is God Himself.

He created matter together with motion and rest in the beginning. Through His ordinary concurrence alone, maintains as much motion and rest in it as He initially placed.

Motion is merely in the body moved, than in its modification.

But it nevertheless has a determinate quantity which remains the same in the entire universe, evem if it changes in its individual parts.

For instance, body A moves twice as fast as body B.

• Body B is twice as large as body A which makes it slower.
• It means that both bodies have equal motion, but different size.

As the motion of one body becomes slower, the motion of the other body equal to it becomes faster [relative to it].

God:

• is immutable in Himself
• operates in the most constant and immutable manner

And so we should not suppose any other changes in His works, lest any inconstancy be attributed to Him.

God moved the matter particles in different ways when He first created them.

He now preserves all this matter in precisely the same way and by the same reasoning as He first created it.

He also always maintains the same amount of motion in it.

37. The First Law of Nature: Each thing always perseveres in the same state as much as it can. thus, what is once moved always continues to be moved.

Certain laws of nature can be known from this same immutability of God.

Such laws are the secondary and particular causes of the motions in individual bodies.

1. Each thing, insofar as it is simple and undivided, remains as much as it can always in the same state. It is never changed except by external causes.

Thus, if some part of matter is square, we easily persuade ourselves that it will remain perpetually square unless something else comes along to change its shape.

If it is at rest, it will not move unless driven by some cause to do so.

If it is moving, then it will keep on moving of its own accord. It will not stop while it is not impeded by any other cause.

Therefore, what is in motion continues to move as much as it can.

Here on earth, all motions near it are soon stopped, often by causes that are hidden from our senses.

This makes us believe that those motions which were thus stopped by unknown causes were stopped by their own accord.

We are inclined to think this of all motions – that they stop by their nature or tend toward rest.

But this is very contrary to the laws of nature. This is because rest is contrary to motion. Nothing can naturally tend toward its contrary.

38. The Motion of Projectiles

Everyday experience with projectiles entirely confirms this First Law.

Projectiles continue in motion for some time after they have left the throwing hand because they continue to move until they are slowed by opposing bodies.

They are usually gradually slowed by the air or any other fluid bodies where they move in.

Therefore, their motion cannot last long.

We can directly experience the air resisting the motions of other bodies by striking it with a fan.

The same is confirmed by the flight of birds.

Air is the only liquid that most evidently resists the motions of projectiles.

37. The first law of nature is that each thing, as far as it is in itself, always continues in the same state, so that which itself is moved, will always continue to be moved.

From this same immobility of God, certain rules or laws of nature can be known, which are secondary and particular causes of various motions that we observe in individual bodies.

The first of these is that every object, insofar as it is simple and indivisible, remains, as much as possible, in the same state, and never changes unless acted upon by external causes.

Thus, if a portion of matter is square, then it will always remain square unless something else comes from outside to change its shape.

If it is at rest, it will not move unless it is impelled by some cause.

If it is in motion, it will never stop of its own accord without being hindered by anything else.

Therefore it must be concluded that what is in motion, as much as it is in itself, is always in motion.

But because we are here on Earth, whose constitution is such that all motions that occur near it are quickly brought to rest, often due to causes that are hidden from our senses.

Therefore, from an early age we have often judged those motions, which are thus stopped by causes unknown to us. This makes us think that they stop of their own accord, that they cease from their own nature, or tend towards rest.