Originally Posted by
Andy_K
I think you're not quite getting your head around how the conservation of energy principle works. The moving bike has kinetic energy. The friction of the pad rubbing against the rim converts that kinetic energy to (mostly) thermal energy.
Energy and force are different concepts, and force can be multiplied through mechanical advantage. The conservation of energy principle doesn't really apply to your hand motion when braking in any useful way. (Technically your body is using a bit of biomechanical energy to get the brake lever and pad moving, but that's negligible in the overall picture, and no physicist would have anything to do with a system as complex as the human body except in abstraction and hand waving.)
What's to misunderstand? Kinetic energy HAS to be disspated to stop. Whether it's thermal or mechanical, it's gotta go somewhere. I'd buy that it's going mostly to thermal, but wondering how the physics work with such little force with the hands. Still not clear to me. If the hands don't do any work, why do we have to still squeeze pretty dang hard on those steep descents?