Originally Posted by
grolby
This turn of phrase really needs to die, it's so misleading. When you pedal your bike, you are not "spinning up" a 1500g pair of wheels. You are using those wheels to apply a force to accelerate your own butt + bike, a mass at least an order of magnitude greater than that of the wheels.
That phrase is fine because it is true. Actually, both are true. There is energy required to increase the rotational energy of the wheels. You also use the wheels as a lever to apply the force that results in that same energy. Yes, the energy needed to accelerate your butt up to speed is more than the energy to spin up the wheels.