A closer look
Isaac Newton said objects accelerate at a uniform rate, but dropping a rock off a building happens too fast for 18th-century stopwatches to prove it. George Atwood got tired of the ambiguity and built a delightfully simple machine: a pulley with two nearly identical masses hanging on either side. By making one mass just slightly heavier, the system accelerated downward at a sluggish, highly measurable pace. It diluted the effect of gravity, allowing students to watch uniform acceleration happen in slow motion, rendering Newtonian physics undeniable even to the thickest of skeptics.
