Ever wonder how the single driveshaft in your car manages to power two (or more) wheels simultaneously? The answer is the differential, a device capable of splitting torque dynamically. There are a variety of different types of diffs, from fully unlocked to more pricey limited-slip models, but none are quite like the one created by Harvard graduate student Pratheev S. Sreetharan and professor Robert J. Wood. Dubbed the PARITy (Passive Aeromechanical Regulation of Imbalanced Torques), it's only five millimeters long and, while such a tiny thing would evaporate if mounted between the rear wheels on a Mustan
