[ Re "James Watt & Watt's Linkage"

Hi All -- I thought I had said about all that could be said about
momentum, inertia, etc., after teaching physics for 30 years but I
cannot contain myself upon seeing recent MMD entries.  I am sure both
gentlemen think they are correct in repeating for us what they call
common usage definitions.  Unfortunately, such definitions are not
acceptable in physics (as many failing physics students have found
out).

The basic, complete definition for inertia (Newton's 1st Law):

  The tendency of objects at rest to remain at rest unless acted upon
by an outside force -- and of objects in motion to remain in motion in
a straight line with a constant velocity, unless acted upon by an
outside force.

The basic definition for momentum (Newton's 3rd Law):

  Mass X Velocity, often described as Action = Reaction.

Also remember that Watt's linkage (or monkey motion) does involve some
rotary motion and Newton _never_ gave us any laws involving rotary
frames of reference or objects in them.  (Hence the term "Straight Line
Physics".)

I am sure those who wrote earlier on these subjects are intelligent,
well informed individuals and I do not mean to belittle them, but as
one who taught in "The Golden Age of Education" I just can't let it
slip by.

Sincerely,
Jim Welty

 [ Thanks, Jim; I feel comfortable with the concepts but I sure
 [ couldn't explain them.  ;-)  -- Robbie