I've got a flywheel spinning at 850RPM. It weighs 112,34g and has a radius of 38mm. I want to calculate the Kinetic energy (Ek) it has given in Wh (watt per hour). Angular speed: ω = n*2pi()/60 = 850*2pi()/60 = 89,011 rad/s Moment of inertia: I = 0,5*m*r2 = 0,5*0,11234Kg*0,038m^2 = 0,00008110948 Kg*m^2 Kinetic energy: Ek = 0,5*I* ω^2 = 0,5*0,00008110948 Kg*m^2*(89,011 rad/s)^2 = 0,321 Joule = 0,321 Ws = 0,321/3600 = 8,916*10^-5. Is this calculation correct? I don't understand how this can be possible. Because it can generate at least 300 milliwatt of power. So I expect the kinetic energy in Wh would be directly connected to how much power it outputs in watt. But that's also confusing... if a generator is generating 300 milliwatt... (5 volt and 60 milliamps), it is generating this per hour???