Imagine I have a lossless rear wheel drive car with a 1:1 differential gearbox in the back. I apply the brakes so the wheels are locked. I apply 1Nm of torque to the input shaft, and observe +/-0.5Nm of torque on each wheel. Now I spin the massive left rear wheel so it's moving freely at 100Hz in one direction, and the massive right rear wheel 100Hz in the other direction. The rotations cancel, and the drive shaft thus remains stationary. Now I apply a 1Nm torque to the drive shaft. Do the rear wheels experience: A: 0.5Nm torque, or B: Some amount of torque inversely proportional to the rotation rate of the wheels? If it's the former, then a small amount of work on the drive shaft (due to low RPM) causes a lot of work to happen in the two wheels (due to the same torque * high RPM) and would be a good work-magnifier (or work-transferrer, since it can't break conservation). If it's the latter, then a differential should make a good torque-magnifier (and thus a great CVT).