Video narration
Why does a charged particle entering a magnetic field at an angle follow a helix instead of a circle or a straight path? Think of a spiral staircase: you move upward steadily while turning around its central axis. The particle's velocity does both at once. Split it into two components: one parallel to the field and one perpendicular to it. Here is the key turn. The perpendicular component feels the Lorentz force, a magnetic force at right angles to its motion. It continually turns that motion without changing its speed, producing a circle. The parallel component feels no magnetic force, so in an ideal uniform field it keeps both its speed and direction. Both motions happen simultaneously around the field direction. Because the perpendicular part circles while the parallel part carries it forward, together they make a helix.