francisco wrote:
let us place a block on a rigid horizontal plane. let the block slide along
this plane. we then observe that it gradually slows down and stops when the
hand initially pushing the block is removed. now using a smoother block and
a smoother plane and providing a lubricant, we note that the velocity
decreases more slowly than before. let us now use an air track and observe
that by tapping the glider, it moves at a slow and almost constant speed.
you can see that if all friction could be eliminated, the body would
continue indefinitely in a straight line with constant speed. an external
force then is needed to set the body in motion, but no external force is
needed to keep a body moving with constant velocity.
Velocity is an artifact of observer coordinate frame. What makes a
Foucault Pendulum alter its plane of swing over time? And when it's
at the Equator?
it is difficulty to find a situation in which no external force acts on a
body,
Minkowski space in a classical vacuum.
but we do not need to go to the vacuum of distant space to study
motion free of external force because there is no distinction between a body
on which no external force acts and a body on which the sum or resultant of
all the external forces (net force) is zero.
Not true. Internal stress from external strain alters the body's
mass. It can also precipitate charge segregation (piezoelectricity),
optical anisotropy, acoustic emission ("tin cry")... If something
comes out anistropically there is a resultant anisotropic back force.
Momentum is conserved.
therefore, consider a body on which no net force acts. if the body is at
rest, it will remain at rest. if the body is moving with constant velocity,
it will continue to do so.
Really? It's been considered independent of you,
Newton, Isaac. 1687, "Philosophiae Naturalis Principia Mathematica"
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
