You should see that the particle moves in a circle, perpendicular to the direction of the magnetic field. But what sets the size of this circle? As the particle is moving, use the slider bars for Mass and Charge to see how properties of the particle affect its motion. You can also use the Strength slider bar to change the magnitude and direction of the magnetic field while the particle is moving. What happens when the sign of the field changes? You can start again by clicking the Reset button. Try that; reset, and then increase the Velocity setting before clicking on Fire! again. What happens now, when the particle moves more quickly?