For the same reason Paul McCartney is known as "Sir": He was knighted by the Queen (a different queen in each case, of course; Elizabeth II isn't that old).
Sir Isaac Newton did not have a nickname. He was simply known as Sir Isaac Newton during his lifetime.
sir isaac newton best known as the finder of the 3 general laws
Sir Isaac newton.
Isaac Newton introduced the 3 laws of motion.
Sir Isaac Newton.
Sir Isaac Newton's main goal was to find a way to produce gold out of different metals. Isaac Newton was best known as an English physicist and mathematician.
Sir Isaac Newton
Sir Isaac Newton.
Sir Isaac Newton
the interests of sir isaac newton were lights
Sir Isaac Newton
Isaac Newton formulated the laws of motion. These should not be confused with the laws of planetary motion by Keplar