The Inertial Balance Kit is a simple demonstration of the principle of determining the mass of an object from the frequency at which it vibrates in a system. In addition it clarifies the difference between mass and weight. We all know that gravity pulling everything towards the centre of the earth is the cause of something having 'weight' and we know that weight and mass are almost equal. However this instrument proves that gravity has no effect in a body having 'mass'. A plate is clamped to the table and a second plate overhangs the table while being connected to the first plate by spring blades that allow the second plate to oscillate back and forth in the horizontal plane only. Weights are placed in the oscillating plate and are either supported by the plate or separately supported by a cord. The timing of oscillations is done by stopwatch.