Answer
The vibration frequency of a clamped hacksaw blade decreases if a piece of clay is stuck to middle of the blade. It decreases further if the clay is moved all the way to the free end.
Work Step by Step
Sticking on a wad of clay increases the moment of inertia (rotational inertia) of the system. The restoring force (the springiness of the blade) stays the same, and so everything vibrates more slowly. This decreases the frequency of oscillation.
Moving the clay farther from the pivot increases the rotational inertia even more, further decreasing the frequency.
Rotational inertia is discussed in Chapter 8.
