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AlephZero
AlephZero is offline
#2
Feb7-13, 11:39 AM
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Most of yuur math is completely wrong, but the marketing guys are right to some extent.

The translational kinetic energy of a mass on the rim (i.e. the energy if the wheel was sliding not rotating) = ##mv^2/2##.

The rotational KE = ##I\omega^2/2##. ##I = mr^2## and ##\omega = v/r##, so the rotational KE also = ##mv^2/2##.

So, in terms effort required to accelerate the bike, a mass on the wheel rim needs twice as much energy as the same mass on the bike frame.

However this is mostly marketing hype, because a mass of 0.15kg is very small compared with the mass of the bike rider. The amount of energy to accelerate a 50kg cyclist compared with an mass of 0.15kg for the wheel rim would be 50/(2 x 0.15) = 167 times bigger.

FWIW the idea behind this is much more important for the rotating parts of an engine in a race car or bike, because the RPM of the engine is much higher than RPM of the wheels.