Originally Posted by
hhnngg1
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?
What's to understand is the distinction between force and energy.
Your hands are providing force, not energy. The force from your hands, combined with leverage from the braking system, presses the brake pads against the rims. That force is perpendicular to the direction of movement, which clues us in to the fact that this isn't a straight 'F=ma' type of deal. The force of the pad against the rim acts more or less (to a certain point) like a multiplier for the frictional force between the surfaces and that friction is what's stopping the bike.