What is Force?
Table of Contents
- As for circular motion, many think that, with increasing true circular motion, a body necessarily tends more and more away from the axis.
But this arises from the fact that, since circular motion can be regarded as originating at every moment from two directions, one along the radius, the other along the tangent.
If impetus is increased in this last direction only, then the moved body will move away from the center, and the orbit will cease to be circular.
But if the forces are equally increased in both directions, the circular motion will remain, but accelerated by an endeavor which will no more argue that the forces of receding from the axis have been increased than those of approaching it.
Water rotated in a bucket ascends to the sides of the vessel because, when new forces are applied in the direction of the tangent to any particle of water, equal new centripetal forces are not applied at the same instant.
The rotating water does not mean that absolute circular motion is necessarily recognized by the forces of moving away from the axis of motion.
Moreover, in what way these words, “forces of bodies and endeavors,” are to be understood, is sufficiently and more than sufficiently evident from the premises.
- A curve can be considered as consisting of infinite straight lines.
- This is useful in geometry.
Likewise, circular motion can be regarded as originating from infinite rectilinear directions.
- This is useful in mechanical philosophy.
However, it is not therefore to be affirmed that it is impossible for the center of gravity of any body to exist successively in the individual points of a circular periphery, no account being taken of any rectilinear direction, either in the tangent or in the radius.
- Some people define the true places of bodies by parts of absolute space.
They think that the motion of a stone in a sling, or of water rotated in a bucket, is circular motion.
This is not correct.
This is because it is compounded of motions not only of the bucket or sling, but also of the earth’s:
- daily rotation around its own axis
- monthly revolution around the common center of gravity of the earth and moon
- annual revolution around the sun.
Therefore any particle of the stone or water describes a line far removed from a circle.
Nor is there really that centrifugal endeavor which is believed to exist.
Thhis is because it does not regard any single axis in relation to absolute space, supposing that such a space exists.
Therefore it cannot be called a single endeavor to which truly circular motion corresponds as its proper and adequate effect.
- Motion can only be recognized or measured by sensible things.
Absolute space does not impinge on the senses. So it must be utterly useless for the distinction of motions.
Besides, determination or direction is essential to motion. But this consists in relation.
Therefore it is impossible for absolute motion to be conceived.
- Furthermore, the motion of a body is relative to many places. A thing can be moving in one respect but at rest in another.
True motion and true rest can be determined by using the relative space enclosed by the heaven of fixed stars, regarded as at rest, in place of absolute space.
But motion and rest defined by such relative space can be conveniently used in place of absolute motion and rest, which cannot be distinguished from them by any symptom.
For however forces are impressed, whatever endeavors there may be, let us grant that motion is distinguished by actions exerted on bodies; nevertheless, it will never follow from this that that absolute space and place exist, and that its change is true place.
- The following stand firm without the calculation of absolute motion:
- the laws of motions and their effects
- the theorems containing their proportions and calculations
- for different figures of paths
- for different accelerations and directions
- for media more or less resisting
The absolute motion of body cannot be known.