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Re: [Phys-L] inertia and the tablecloth demo



Two comments
First the notion of at rest is a fiction since it depends on your inertial frame of reference.
Second. It seems to me that in spite of our understanding there is still an element of mystery associated with the way objects continue to move in the absence of a force, so we need a cause so we give the object a property we call inertia. In that sense ir is an empty concept in a Newtonian world and has a deferent only in an aristotlean world

Best

Joe

Sent from my iPhone

On Aug 18, 2016, at 10:55 PM, Anthony Lapinski <alapinski@pds.org> wrote:

I would not equate the first law with conservation of momentum. If an
object is at rest, it has no momentum but still has mass (intertia).

On Thu, Aug 18, 2016 at 10:40 PM, Richard Tarara <rtarara@saintmarys.edu>
wrote:

Except that Newton's First Law is often referred to as the Law of
Inertia. I think most here would say that the first law is about momentum
and the conservation of such in the absence of external net forces. I used
to have an animation that I used in class showing how an astronaut in space
could be crushed between two 'weightless' elephants. In reality they
worried about getting crushed between the shuttle and Hubble. So, at least
in my mind, inertia has been used not just for mass but for something
moving that is difficult to accelerate (usually to stop or deflect). Yes,
the main focus is on the mass, but not exclusively so, or so it seems to me.

rwt

On 8/18/2016 7:35 PM, Jeffrey Schnick wrote:

I consider mass and inertia to be the same thing. Inertia is the word
one tends to use when one is talking about the concept and mass is the word
one tends to use when one wants to assign a value to it. It is often said
that "Mass is a measure of inertia." (That phrase, in quotes, gets 65,100
hits on Google.) I prefer "Mass is inertia." which only gets 18,200 hits.

--
Richard Tarara
Professor Emeritus
Saint Mary's College

free Physics educational software
http://sites.saintmarys.edu/~rtarara/software.html

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