Outline
The theory of mechanics presented by Sir Isaac Newton in 1687 is the foundation of classical mechanics and modern physics. This article relates to his work by first considering velocity and acceleration. For EthnoPhysics, these dynamic concepts are logically defined from sensations, and quantified by measurement. Then we develop the notion of force based on Newton’s second law of motion. His first law is used to define straight lines and linear motion. And finally, Newton’s third law is interpreted as a scientific reiteration of venerable knowledge that can be traced back as far as the Vedic literature . These widespread ancient ideas about cause and effect are often referred to as karma .
Velocity
Consider a particle P described by a repetitive chain of historically ordered space-time events
Let these events be characterized by their position
and time of occurrence
Then we write
The separation between some arbitrary initial and final pair of events is given by And the elapsed time between these events is
Then a velocity vector is defined by the ordered set of three numbers
The speed of P is defined by the norm of the velocity
Consider measuring this quantity based on observations of length and time. Recall that length is defined only for particles that are at least as big as atoms. And we also presume that P is compared to a frame of reference that includes a calibrated rod and a calibrated clock To determine the velocity first measure the elapsed time between events
and
as
where is the number of clock cycles between initial and final events,
is the period and
is the frequency of P. Then make three length measurements along the spatial axes that are noted by
and
Combine these measurements to obtain the observed separation vector
between events. This separation is due to a sum of displacements that may be written as
where notes the displacement of P during one complete orbital cycle
. As discussed earlier atomic cycles are separated from each other by one wavelength
And if measurements are not too disruptive so that
is constant, then the distance between initial and final events is
Combining these observations gives the measured speed of P as
If P contains many quarks we can use Planck’s postulate to substitute the mechanical energy for the frequency to obtain
And if the frame of reference is inertial then de Broglie’s postulate can be used to replace the wavelength with the momentum to obtain
The Speed of a Photon
If the particle under consideration is a photon then its mass
is zero, and its energy is given by
Substituting this into the expression for speed developed above gives
And so the constant number is usually called the speed of light. For photons
Thus the wavenumber
and other photon characteristics are all related as
The Speed of a Newtonian Particle
If P is Newtonian then and the particle is presumably in dynamic equilibrium with its environment. For this case, the mechanical energy is given by
where
is the kinetic energy. So for Newtonian particles
But recall that kinetic energy is defined by So for Newtonian particles
This equation can be rearranged to obtain the conventional statement
The term momentum is the modern English word used for translating the phrase; quantity of motion.1Isaac Newton, Mathematical Principles of Natural Philosophy, page 639. Translated by Andrew Motte and Florian Cajori. University of California Press, 1934. So the foregoing relationship was articulated by Sir Isaac Newton when he wrote2Isaac Newton, Mathematical Principles of Natural Philosophy, page 404. Translated by I. Bernard Cohen and Anne Whitman. University of California Press, 1999.
Quantity of motion is a measure of motion that arises from the velocity and the quantity of matter jointly.
— Sir Isaac Newton
This direct proportionality between speed and momentum is traditional and simple. It can be used to eliminate the momentum in some previously defined quantities such as the Lorentz factor which can now be expressed as
And for Newtonian particles the kinetic energy can be written as
Acceleration
Consider a particle P described by a repetitive chain of historically ordered space-time events
Let these events be characterized by their position
and time of occurrence
We express this trajectory of P by writing
Use these characteristics to calculate a velocity for each event
Then changes between some arbitrary initial and final events are noted by
The acceleration vector is defined by the ordered set of three numbers
This acceleration is used to describe changes in the trajectory of P. It can be experimentally determined by measuring lengths and elapsed times. The norm of the acceleration is written without an overline


Force and Newton’s Second Law
Consider a particle P described by a repetitive chain of historically ordered space-time events
Let these events be characterized by their position
and time of occurrence
We represent this trajectory of P with the expression
These characteristics may be used to establish the momentum for each event
Then let P interact with some particle called
between initial and final events so that there is a change in P’s motion described by
According to the usual narrative of Newtonian mechanics, the particle impresses a force like a push or a pull that causes the change in P’s motion. Sir Isaac Newton says that3Isaac Newton, Mathematical Principles of Natural Philosophy, page 416. Translated by I. Bernard Cohen and Anne Whitman. University of California Press 1999.
— Sir Isaac Newton
This relationship is called Newton’s second law of motion. It can be mathematically expressed by defining an algebraic vector called the force as
If P is a Newtonian particle in dynamic equilibrium, then its momentum is related to its velocity by where
is its mass. Also for many sorts of interactions the mass of a Newtonian particle can be considered constant, then
and the force can be written in terms of the acceleration
as
Momentum is conserved. So all particles that have momentum can cause changes in the momentum of another particle if they are absorbed or emitted. Then X, the particle that is absorbed or emitted, is often called a force-carrying particle.
Force-carrying particles that are material or charged are usually easy to detect in the immediate vicinity of an interaction. So the forces they impart are called contact forces. Phenomena like automobile collisions and gunshot wounds can be understood using contact forces. X is much less conspicuous if it is ethereal and neutral. Such particles can be difficult to detect, and the forces that they carry may seem to come from far away. So they are often referred to as exchange particles to suggest a remote origin, and their effects are called action-at-a-distance forces.
If X is imaginary then its force may seem like some random background fluctuation coming from nowhere specific. Many of these force-carrying particles are difficult to characterize and distinguish as individuals, so it is often more convenient to group lots of them together and refer to them collectively as force fields. For example we may vaguely refer to a set of photons as an electromagnetic field, or a collection of gravitons as a gravitational field.


First Law of Motion
Consider a particle P described by a repetitive chain of historically ordered space-time events
Let these events be characterized by their position
and time of occurrence
We express this trajectory of P by writing
These characteristics may be used to establish the momentum for each event
By the second law of motion, any change in the momentum of P is related to the action of some force
that is described by
So if there are no forces acting on P, then there are also no changes in P’s momentum, and vice versa
The forgoing statement is just a special case of the second law of motion. Yet Newton included this null relationship as part of his first law of motion. It may seem redundant, but the first law is more than simply a special case of the second law because it also establishes exactly what is meant by a straight line segment or a straight rod. The first law is also known as the law of inertia, it has been translated4Isaac Newton, Mathematical Principles of Natural Philosophy, page 416. Translated by I. Bernard Cohen and Anne Whitman. University of California Press 1999. into modern English as
— Sir Isaac Newton
For EthnoPhysics this first law is uniquely important because by our premise we prefer to avoid mysteriously received knowledge about length and lines. So this aspect of Newton’s first law is formally restated in the following explicit definition: If P has the same momentum for all events in its trajectory, then describes uniform linear motion and we say that P is moving in a straight line. This sort of force-free motion is obtained if the frame of reference is inertial and P is isolated It is only well-defined for particles that are at least as big as atoms.
Collisions and Explosions
Here is an archetypal vignette from Newtonian mechanics. Two atoms called and
have an interaction with each other by swapping another particle,
, which is called the exchange particle. The interaction is caused when
emits
at event
which is called the initial event of the interaction. This is written as
Particle then has an effect on
by being absorbed at event
which is called the final event of the interaction. We express this by writing
For EthnoPhysics, the interaction is described using three repetitive chains of historically ordered events written as
Since and
are composed from atoms, we assume that they can be described by space-time events with a position
and time of occurrence
. We do not assume that
is an atom, rather we often take it to be a photon or a graviton. So we cannot always describe
using a trajectory. And the position of
is well-defined only for the initial and final events where it is included as part of an atom. Overall, the interaction is characterized by the following quantities.
Momentum Change by Emission
The interaction is caused when emits
at an event
which is called the initial event of the interaction. We write
But momentum is conserved so a total over all momenta
are the same before and after the interaction
Then the change in ‘s momentum due to the emission of
is given by
Momentum Change by Absorption
Particle has an effect on
by being absorbed at event
which is called the final event of the interaction. We write
But momentum is conserved so a total over all momenta
are the same before and after the interaction
Then the change in ‘s momentum due to the emission of
is given by
Karma and Newton’s Third Law
The third law of motion from Sir Isaac Newton is about a balance between the forces of cause and effect. It has been translated5Isaac Newton, Mathematical Principles of Natural Philosophy, page 417. Translated by I. Bernard Cohen and Anne Whitman. University of California Press, 1999. as
— Sir Isaac Newton
This has something in common with the ancient Indian idea of karma a key concept in Hindu, Jain, Buddhist, Tao, Shinto and Sikh philosophies. It is also similar to Western aphorisms like, ‘what goes around comes around’. And we suppose that Newton himself was well aware of passages in the Jewish and Christian texts about reaping and sowing.
But Newton’s third law is much more than just a vague claim of cosmic balance. It has a scientifically precise expression in terms of two atoms called and
that have an interaction with each other by exchanging a third particle called
The interaction begins when emits
As discussed earlier, the momentum change due to this event is given by
The emission causes the effect of
being absorbed into
. The momentum change due to absorption is
The elapsed time between emission and absorption is noted by
. The forces acting on
and
are found by substituting their momentum changes into the definition of force to obtain
so the force of the cause is of equal size and in the opposite direction to the force of the effect.
Thus Newton succeeded in articulating a wisp of widespread karmic wisdom. His approach leads to the enormous benefit of being susceptible of scientific investigation. Its range and accuracy can be tested in our laboratories. This process of measuring and checking is what makes Newtonian mechanics so trustworthy.


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1 | Isaac Newton, Mathematical Principles of Natural Philosophy, page 639. Translated by Andrew Motte and Florian Cajori. University of California Press, 1934. |
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2 | Isaac Newton, Mathematical Principles of Natural Philosophy, page 404. Translated by I. Bernard Cohen and Anne Whitman. University of California Press, 1999. |
3, 4 | Isaac Newton, Mathematical Principles of Natural Philosophy, page 416. Translated by I. Bernard Cohen and Anne Whitman. University of California Press 1999. |
5 | Isaac Newton, Mathematical Principles of Natural Philosophy, page 417. Translated by I. Bernard Cohen and Anne Whitman. University of California Press, 1999. |