Originally Posted by
framer
ahhh ok thanks. I’m not really interested in that as much as the difference between a 90 degree turn onto the centerline, brining the thrust to 40% while stationary v’s rolling onto the runway at 8-12 kts with engines spooled up at 40% and then pressing TOGA once aligned with the centerline. Obviously if you roll out at taxi speed you are chewing up runway distance but I think what Boeing is saying is that the kinetic energy you have when you press TOGA using that method is similar ( negligible difference) to the energy you would have at the same spot if you had done a 90 degree line up. Where are the physics geeks?
I'm not sure how useful this is, but this is the physics you asked for (I hope):
Kinetic energy grows with the square of the speed.
Therefore, if you have 10% of your final speed, you have only 1% of your final kinetic energy. Neglible.
(Regardless of weight.)
Rotational energy of the turbines is proportional to the square of the rpm, so 30% vs 40% N1 would be 9% vs 16% of the rotational energy of the turbines at 100%.