56 The Poetry of Physics and The Physics of Poetry
he completely transformed the nature of physics and the expectations
of physicists who would never again be satisfied with anything less
than a mathematical description of nature. Newtonian mechanics also
influenced the non-scientist worldview ever after. But before explaining
this let us consider the rudiments of Newtonian mechanics.
Perhaps the most important aspect of the Newtonian worldview is the
way in which motion is regarded. For the early Greeks motion per se was
not a natural thing and all motion had to be explained in terms of some
force. Motion was often taken as evidence for the animation of the
moving object. For the Newtonian on the other hand uniform straight-
line motion (or constant velocity motion) is the natural state for any body
and does not require an explanation. Any deviation from constant
velocity, however, such as slowing down, speeding up or changing of
direction must be explained in terms of some force. According to the
Newtonian view once an object has attained a constant velocity in will
retain that constant velocity until some force acts to change that velocity.
We have all experienced this property of our own body, which we
usually refer to an inertia. Perhaps you can recall being a standing
passenger on an autobus and flying forward when the driver suddenly
applied the brakes. By applying the brakes the driver produced a force,
which slowed down the autobus. This force did not operate on you,
however, and consequently you continued moving at the same speed,
which is now greater than that of the bus and hence for an instant you
traveled in the forward direction faster than the bus and hence
experienced being thrown forward with respect to the bus. Actually what
happened in that instant was that your motion remained the same and the
bus was thrown backwards with respect to you by the force of the brakes.
A similar thing happens when a passenger car suddenly turns to the left
and we experience being pushed to the right. Once again our constant
speed straight-line motion is unaffected by the force which makes the car
change its direction. The car goes to the left and we go straight but with
respect to the car we go to the right.
The principle of inertia serves as the foundation of Newtonian
mechanics. Each particle is described by its mass, its position and its
velocity. The mass of a body is a measure of the amount of matter it
contains and is related to its weight. The actual weight of an object on
Earth for example is a measure of the gravitational pull the Earth exerts
on the object and is directly proportional to its mass. The same object on
the Moon will weight less because the Moon’s gravitational field is