The motion of ions in quadrupole field spectrometers was simulated using large particles (10–40 μ diam) that can be visually observed, with appropriate scaling of the voltage and frequency parameters. In air, the motion of the large particles is damped by the viscous medium, but their stability properties are still governed by the Mathieu equation. A new method is suggested for pulsing ions out of the 3-dimensional quadrupole mass spectrometer.