If you have a perfect circle that is one unit in diameter (one inch, one centimeter, one foot, whatever you choose from one point to the exact opposite point), then the distance around the circle will be pi units around.
the same atom, existing at the same moment in time, about ten times its diameter from each other. It's like a happy you and a sad you standing ten feet apart looking at each other.
There was a time that we believed these laws covered everything. Then we discovered that the laws of Newtonian physics fail at the sub-atomic level. Heisenberg's Uncertainty Principle basically proved this.