Keys and MOI - wipp assist

[Richard Brekne]

"Don A. Gilmore" wrote:
> 
> Hi Ric:
> 
> No, I think John is just converting mass to force on earth.  You have to
> multiply grams by the acceleration of gravity to get the force they exert
> downward on earth (the "weight").  It doesn't have anything to do with the
> acceleration of the object by outside forces.
> 
> W = m * g
> 
> where W is weight, m is mass and g is the acceleration of gravity.
> 
> It's common for folks to confuse weight with mass.  They are really two
> different things.  Grams are mass, not force.  The units that John shows
> 
> g-cm/s^2
> 


Thanks Don... I was pretty sure thats what he meant... just needed a
clarification.... I mean you never know ... grin.. Typos are best
cleared up by the authour, not the questioner.


> are actually units of force, believe it or not.  Usually this would be
> converted to "dynes"
> 
> 1 dyne = 1 g-cm/s^2


Ok on the force bit... but the "dyne" is an unfamiliar term...Thanks
muchly for the explaination below, but I am unsure as to whether or not
John consciously used dynes... I mean... why use them in this case ? And
why was an explaination in terms of ergs lacking then. No matter really.
But for fun.. lets see... John cited a BW force of "45gm*980cm/sec^2 -
10gm*980cm/sec^2"... that would be 35 dynes then eh ? 


> 
> "But hold on, Gilmore, what is this 'dyne' nonsense?"  Well, since F = ma,
> force actually has units of mass times acceleration, or
> mass-times-distance-per-time-squared.  So that we don't have to write out
> these big units, a hybrid unit was created.  John has elected to use cgs
> (centimeter-gram-second) units, which are used mainly in theoretical physics
> and chemistry.  The unit of force in this system is the "dyne".  The unit of
> energy would be the "erg", which is a dyne-cm.
> 
> In all of my posts I use the more common MKS system (meter-kilogram-second),
> which is used in all branches of engineering.  The unit of force in the MKS
> system is the "newton"
> 
> 1 N = 1 kg-m/s^2
> 
> And energy is in units of a "joule", which is a N-m.  There are 100,000
> dynes in a newton, so they are very, very small.  The MKS system is used
> because it relates better to all the other areas of engineering.  Volts and
> Amperes, for example, are MKS units (volts can actually be expressed in
> meters, kilograms, seconds and coulombs).

Ok... this is neat to know really... We could speak in terms of Calories
I suppose if we wanted to... but which would you say is best to use for
our present application... newtons or dynes ??

> 
> If using the English system, distance is in feet, mass is in slugs and time
> is in seconds.
> 
> 1 pound = 1 lb = 1 slug-ft/s^2
> 
> English energy is in ft-lbs (there is no hybrid unit).

Ahhh.... so thats where the "sluggish" terms thrown around the last
couple days come in. 

> 
> Hope this helps!
> 
> Don A. Gilmore

Sure it does... The more we get familiar with physics terms and concepts
as they are meant to be used the better. Some of our throng are more
familiar then I, some less... but most of us benifit from this kind of
post methinks... Thanks muchly Don

Cheers
RicB