No Twisting Out of Newton’s Law

ScienceNow : The harder you push a sled across a frozen pond, the faster it accelerates. In 1687, Isaac Newton quantified this most basic bit of physics with his second law, which states that the force applied to an object equals its mass times its acceleration (F=ma). Now scientists have verified this law with unprecedented precision, challenging critics who have suggested the rule somehow bends for very small accelerations.