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Confidence votes 317. Inertia is rotary momentum; an object's ability to continue spinning when a decelerating force is applied. Just as a heavy object takes more effort to stop from the same speed as a light object, so does a heavy object take more effort to stop from turning at the same speed as a light object. So assuming they are turning at the same angular velocity, the heavier one has a larger inertia.
Another way of thinking of this is to say that gravity has to pull harder on a heavy object than a light one in order to speed them both up by the same amount. However, in the real world, we have things like air resistance, which is why sometimes heavy things do fall faster.