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Re: [Phys-l] The "why" questions





-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of D.V.N. Sarma
Sent: Monday, November 29, 2010 8:08 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] The "why" questions

John Denker <jsd@av8n.com> wrote:


Absolutely not. As functions of time, F(t) = ma(t). It is the
same t. The law of motion insists that there is no temporal
sequence.

We do not have any point masses in the universe. For a body of
finite dimensions, it is the elastic properties that communicate
the force applied at one end to the other end. There is a time gap.

I think all of us agree that force and acceleration are two different
concepts independent of each other.

I like the definition of force given by Thomas Moore in Unit C of his
set of books Six Ideas That Shaped Physics see:
<http://www.physics.pomona.edu/sixideas/>
It's the same definition given by Ben Crowell on page 143 of his book
Simple Nature. See
<http://www.lightandmatter.com/area1sn.html>
namely, that the net force being exerted on a system is (by definition)
the net rate at which momentum is being transferred to the system.
Consider a nonrelativistic case in which no mass is being transferred to
a system. In such a case the rate at which the momentum of the system
is changing and the mass times the acceleration of the object are one
and the same. The distinction between ma and F comes down to the
distinction between the rate at which the momentum of the system is
changing and the rate at which momentum is flowing into the system.

I see an analogy between the relationship between force and acceleration
and the relationship between the electric field and the electrostatic
force.

In the case of force and acceleration: The acceleration of an object
depends on an inherent property (namely the reciprical of its mass) of
the object and on a property of the environment in which the object is
situated. Starting with the acceleration of an object, if you divide
out the inherent property of the object, you are left with the
property-of-the-environment part, namely the force. So the force is
just the <<acceleration per reciprocal-mass>>.

In the case of the electric field and the electrostatic force, the force
on a charged particle depends on an inherent property (namely the
charge) of the particle and on a property of the environment in which
the particle is situated. Starting with the force on the charged
particle, if you divide out the inherent property of the particle, you
are left with the property-of-the-environment part, namely the electric
field. So the electric field is just the <<force-per-charge>>.

The question is, "What is the
relationship between them?"

Our knowledge of the world including that of physics is through the
sensory
interactions our consciousness with the external world. The analysis
of this experience leads us to the cause and effect relationship.
There is no way we can eliminate our consciousness and our
memories and their analysis and retain physics.
For a person who has no sensory interaction with the external world,
leave alone physics, there is no world.

regards,
Sarma.
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