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Re: [Phys-L] [External] Re: causality

A beautiful piece of music suddenly plays from a speaker.You hear it simultaneously as it is played. You simultaneously and concurrently feel a sense of pleasure from the experience.


Is there a cause and effect acting here? Or is your sense of please as much an originator of the music as the music is an originator of the pleasure. Or is neither one causing the other?


Bob at PC

________________________________
From: Phys-l <phys-l-bounces@mail.phys-l.org> on behalf of Marx, David via Phys-l <phys-l@mail.phys-l.org>
Sent: Thursday, February 7, 2019 10:43:52 PM
To: Phys-L@Phys-L.org
Cc: Marx, David
Subject: [External] Re: [Phys-L] causality

Equations such as Newton's second law of motion or Ohm's law provide a relationship between three physical variables. Rather than a causal relationship, we may sometimes prefer to write one form of the equation rather than another, though all are mathematically equivalent.

For example,

I prefer writing I = V/R for Ohm's law when first introducing it for the simple circuit containing only a resistor and a battery.

The current in the circuit is determined by the potential difference of the battery across the resistor and its resistance.

Writing V = IR first does not give the same physical understanding of the relationship.

Similarly, I prefer a = F/m when first talking about Newton's second law because one can see that the acceleration you get is determined by the net force and mass of the object. I do not say the acceleration is caused by the net force. Written in this form, we can talk about the direct relationship between force and acceleration and the inverse relationship to object mass in meaningful ways that are less obvious when you write F = ma.





-----Original Message-----
From: Phys-l <phys-l-bounces@mail.phys-l.org> On Behalf Of Jeffrey Schnick
Sent: Thursday, February 07, 2019 9:26 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] causality

I've been thinking about this example (Newton's 2nd Law) and other continuity equations. I see Newton's second law as a continuity equation which I see as being synonymous with a conservation law. For some system, say a brick, the force on the brick is the rate at which momentum is flowing into the brick and the rate of change of momentum of the brick is what we often represent as the mass times the acceleration of the brick. The total momentum of the brick is changing right there at the boundary where the incoming momentum is crossing the boundary. Any change in the total amount of momentum inside the boundary (between the closed surface of the brick and the rest of the universe) is occurring at the exact same instant as the momentum crosses the boundary. I can't see any cause and effect when the two things occur simultaneously. Is the momentum of the brick changing because momentum is flowing across the boundary or do we judge there to be momentum flowing across the boundary because it is decreasing at the boundary on one side of the boundary and increasing at the boundary at the other side of the boundary. Epstein, in his book, Relativity Visualized, refers to the statement that force causes acceleration as (something like) the great myth of the physics community. I confess to using the cause and effect language but I don't really think force causes acceleration.

-----Original Message-----
From: Phys-l <phys-l-bounces@mail.phys-l.org> On Behalf Of Alex. F. Burr via
Phys-l
Sent: Thursday, February 7, 2019 10:02 PM
To: Phys-L@Phys-L.org
Cc: aburr@aol.com
Subject: Re: [Phys-L] causality

As well as anybody might.jsd is right and insightful as usual. but there is
more. Consider a one dimentional systen of a mass (and reference frame).F
= ma and a = F/m. Notice that the equation and math says nothing about
causality. But the physics says the F most likely causes the a. Newton is
celebrated as the physicist who suggested this.
Physics is not math and vice versa.
Alex. F. BurrIn a message dated 2/7/2019 1:15:22 PM Mountain Standard
Time, phys-l@mail.phys-l.org writes:

Still having some issues with causality.
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