PX155 - A1 - newton's first law

• newton's framework for quantitatively understanding a huge range of the physical world
• a few basic principles
• experimentally based

first law

• "every body continues in its state of rest or uniform motion unless acted on by an external force"
  or
  -"a body moves at a constant velocity unless acted on by a force"

• [N1] holds in "inertial frames of reference", i.e. not accelerating