Answer
A long tine in a tuning fork has a relatively high moment of inertia (rotational inertia) compared to a short tine.
Work Step by Step
The restoring force (the springiness of the tine) is roughly the same in both forks, and so the tuning fork with longer tines will vibrate more slowly, i.e., the frequency of oscillation is relatively low.
Rotational inertia is discussed in Chapter 8.
