All this recent talk of torque and horsepower leads me to show my ignorance and ask for enlightenment (I tried to post this yesterday but it seems I failed, sorry if its a dup): Say I want to spin a nicely balanced wheel. I can calculate the moment of inertia but can't quite grasp how that helps me figure out how big a motor I need. My problem is dimensional analysis: moment of inertia == kg·m² energy (joules) == kg·m²·s² (or Newton-Meter) torque(joules/radian) == kg·m²·s² (where wiki sez: "A torque of 1 N·m applied through a full revolution will require an energy of exactly 2π joules.") So... ignoring friction, the torque of the motor only influences the acceleration of the wheel? Then it is just friction that prevents me from driving my truck tire with a cell-phone vibrator motor? Or is there another conversion I must yet undergo?