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## Main Question or Discussion Point

I have 3 x Flywheels of equal dimensions but different weight eg a.400lbs b.800lbs c.2000lbs,which one will keep turning the longest? Or is there no difference?

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I have 3 x Flywheels of equal dimensions but different weight eg a.400lbs b.800lbs c.2000lbs,which one will keep turning the longest? Or is there no difference?

- #2

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- #3

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But when equal amount of friction is assumed to act on all three flywheels, then the flywheel with maximum rotational kinetic energy will rotate longer.

Rotational kinetic energy=(mass moment of inertia * (angular velocity)^2)/2

Notice that the formula for rotational kinetic energy is similar to kinetic energy formula in linear motion.

Mass moment of inertia is the rotational counterpart of mass(inertia) in linear motion,

Mass moment of inertia = mass * (radius of gyration)^2

Radius of gyration is a measure of how far the mass is distributed away from the axis of rotation.

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- #5

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Friction is directly proportional the normal force. This means it's also directly proportional to mass, so doubling the mass will double the friction.

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