What is Inertia

[Don A. Gilmore]

Hi Isaac:

You're right on the money...up until you include gravity.  Gravity doesn't
affect inertial effects.  An object's mass (or m.o.i.) is the same whether
it is on earth, in space, or on the moon.  An object is just as hard to
accelerate in space as it is anywhere else.  What is seemingly
counter-intuitive here may be that there would be less weight and so less
friction with the floor on the moon if you pushed an object.  But friction
is separate and independent from inertia.  Playing billiards on the moon
would be essentially identical to playing on earth (except with jump-shots
obviously).

Don A. Gilmore
Mechanical Engineer
Kansas City

----- Original Message ----- 
From: "Isaac sur Noos" <oleg-i@noos.fr>
To: "Pianotech" <pianotech@ptg.org>
Sent: Wednesday, December 24, 2003 12:27 PM
Subject: RE: What is Inertia


> But, Terry, the original post you answer too say exactly the opposite
> .
>
> As others (or I am wrong myself) you have hard times to accept the use
> of mass as the expression of inertia, and the kinetic energy or
> torque, as expression of force.
>
> As Inertia does not seem to be a force but the expression of gravity
> (I am may be off on that one !) the only moment we have to deal with
> it is when we play piano in higher level in space (as on this list)
> while not subjected to common gravity.
>
> > An object's inertia is directly related to its mass and
> > velocity. The more  mass it has and the faster it is traveling, the
> more  inertia it has. A
> > bullet, traveling at some very high velocity, could have a
> > similar amount  of inertia as a very slowly moving locomotive.
>
> What you talk about is kinetic energy not even moi.???
>
> That should be more encouraging to keep the physicians on the list if
> we try  to accept the use of the good terms after they took effort to
> explain what it was about.
>
> I believe it is probably helping to stay away from the word inertia,
> as stated it is not a quantity, and it is applied differently
> depending of the context (kinetic or linear).
>
> For instance it is hard to stop me from writing on the list, but I
> don't have much inertia I guess <G> for the mass we'll see that after
> tonight dinner !
>
> Good grief anyone
>
>
>
> Isaac
>
>
>
>
> >
> > Terry Farrell
> >
> > ----- Original Message -----
> > From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
> > To: "College and University Technicians" <caut@ptg.org>;
> > "Newtonburg"
> > <pianotech@ptg.org>
> > Sent: Wednesday, December 24, 2003 6:22 AM
> > Subject: Re: What is Inertia
> >
> >
> > >
> > >
> > > "Don A. Gilmore" wrote:
> > > >
> > > > There are no units of "inertia"; one  object cannot
> > have more "inertia"
> > than another.  It can have more kinetic
> > > > energy, or momentum, or mass, or velocity, or indeed
> > "moment" of inertia
> > > > than another object since those are measurable,
> > quantifiable properties.
> > >
> > >
> > > I understand exactly what you are saying, as I understand
> > exactly what
> > > the others are saying. But I have to point out (without taking a
> > > position on the matter myself) that there are three
> > declared definitions
> > > for inertia on pianotech by various folks with some
> > degree of physicis
> > > knowledge. Let me list them.
> > >
> > >
> > > 1. Don Gilmore... inertia is a concept, not a quantity,
> > has nothing to
> > > do with size, mass, velocity or anything else. Is simply
> > the fact that
> > > objects with mass tend to resist any change in velocity. No object
> > > regardless of mass has any more inertia then any other mass.
> > >
> > > 2. Sarah and Mark.... inertia is very much like Don describes, yet
> > > inertia is mass related... a larger mass will definatly have more
> > > inertia then a smaller mass.
> > >
> > > 3. Jim Ellis.  inertia is clearly mass related its very
> > hard to read his
> > > definition without concluding he means that inertia is related to
> > > acceleration and /or velocity... That  relation to
> > acceleration seems a
> > > bit unclear... but as I read through his posts I get that he first
> > > said... Inertia = mass x velocity-squared, then after some debate
> > > changed this to Inertia = mass x acceleration-squared.
> > His last post
> > > seemed to draw this up a bit differently
> > >
> > > "Inertia is a minifestation, a property, an effect, of
> > acceleration and
> > > deceleration.  It's proportional to the square of the
> > change in speed,
> > > or velocity."
> > >
> > > What I'd like to see at this point is that since Don,
> > Sarah, Mark, and
> > > Jim all are people we all rely on for physics insights,
> > and because they
> > > all present clearly different definitions of this
> > concept,,, that these
> > > four all bang this one through until they arrive at a
> > common definiton
> > > for us.
> > >
> > >
> > > grin.... NOW I will state my own position...
> > tentatively...ok ?? :)
> > > Seems to me that Don is correct... except I have a hard time
> > > understanding or accepting that "one  object cannot have
> > more "inertia"
> > > than another". If this is true then either inertia is a
> > constant, or
> > > inertia is just plain undefined... as in divideing by
> > zero more or less.
> > > So I lean towards Sarah and Mark. But I want to see you 4
> > hashing this
> > > out so we can past the problem.... as clearly any discussion about
> > > action mechanics on this list is going to be rather
> > meaningless unless
> > > we can agree on what terms like inertia mean.
> > >
> > > Cheers
> > > RicB
> > > _______________________________________________
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> > >
> >
> >
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